Search

Multi-model ensembles have become a standard tool for assessing global climate change impacts. Interpretation of such ensembles is complicated because each model group has a different modeling concept and framework. For example, global scale land surface, water and vegetation models have been widely applied to understand the complex hydrological cycle of the Earth and to assess associated past and future changes. Additionally to this purpose, land surface models assess energy and biogeochemical cycles while vegetation models assess vegetation and carbon cycles. Therefore, all these models differ with respect to the specific processes of the hydrological cycle included in their structure. In this study, we demonstrate how the similarities and differences between models can be better understood and illustrated by using a standard representation of the main model features. We analyze twelve models from the global water sector of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) phase 2b: six land surface models (LSMs), five global hydrological models (GHMs) and one dynamic global vegetation model (DGVM). The majority of the models are run with a daily temporal resolution and with a spatial resolution of 0.5°. Part of these models include a reservoir scheme and water use sectors. The heuristic mappings of the models are designed to ensure the opportunity to choose a model at the initial stage of the analysis, based on the most important qualities, relationships and characteristics, which provide users with significant time saving. Therefore, the review study will provide the basis for: (i) achieving further model (inter)comparison; (ii) selecting the right model(s) output(s) for specific applications; and (iii) assessing the similarities and differences among the models. The models characteristics will be presented in three levels of complexity allowing to reach a large audience. The target audience includes the modeling community, the stakeholder community, and the general public interested in understanding large-scale models, simulating climate change and its impacts. Additionally, stakeholder insights, gathered mostly in Eastern Europe and West Africa, have been considered in the study design. Stakeholders were identified according to their need for climate-impact information provided within the ISIMIP framework and included academics, government officials, employees working in international organizations, NGOs, consultancies, and private companies. In conclusion, the presentation describes the study approach and preliminary results, with particular emphasis on the standard model diagram, differences between the models, and the stakeholder engagement. [ABSTRACT FROM AUTHOR]

Earth's critical zone, which spans from the top of the vegetation canopy to bottom of the aquifer, provides a systematic framework for integrated studies of air, biota, soil, rocks, and water. However, the complex structure and interactive processes make many challenges to research this zone. Recently, the booming of hydrology, which interacts with other disciplines in the form of subdisciplines such as hydropedology, hydrogeology, and ecohydrology, has greatly promoted the development of critical zone research. Therefore, this study focuses on the role of water playing in the Earth's critical zone:water shapes the three-dimensional network of critical zone structure; water cycle coupled with biogeochemical process maintains the critical zone function and service; and the hydrology-extended model helps to simulate the critical zone evolution. Overall, this study proposes a conceptual framework that integrates the above three topics, and try to reveal the fundamental issues to be addressed for further advancing Earth's critical zone science. [ABSTRACT FROM AUTHOR]

Land evaporation is an essential component of the climate system linking different bio-geochemical cycles. Yet, it is one of the most uncertain components of the hydrological cycle in terms of magnitude and spatio-temporal variability. Over the last decades, much effort has been put on developing and advancing techniques to accurately measure or estimate this flux remotely. The Global Land Evaporation Amsterdam Model (GLEAM) is a conceptual model designed to estimate land evaporation – and its separate components such as transpiration – from a wide variety of satellite observations and at global scales. The model calculates potential evaporation using the Priestley and Taylor equation and applies multiplicative evaporative stress factors based on root-zone soil moisture and vegetation state to convert potential into actual evaporation. The root-zone soil moisture is calculated using a simple water-balance model. Several studies have already investigated the potential to improve the estimated root-zone soil moisture through the assimilation of satellite observations, ultimately aiming at better estimating land evaporation. Given the wealth of satellite-based datasets of soil moisture, and the specific coupling of soil moisture and the evaporative flux in GLEAM, different approaches to optimally incorporate these datasets into GLEAM have been considered in the past. While the default version of the model adopts a rather simple Newtonian Nudging scheme to assimilate surface soil moisture datasets into GLEAM, other studies have investigated the potential of more advanced Kalman filtering techniques. Also, the direct assimilation of active radar backscatter coefficients and passive radiometer brightness temperatures through the coupling of GLEAM to a set of radiative transfer models has been investigated. These studies have mainly focussed on improving the soil moisture estimates of GLEAM, while current efforts are exploring the potential of assimilating satellite observations related to the state of vegetation, such as land-surface temperature and sun-induced fluorescence. In the future, obstacles to jointly assimilate these different geophysical variables into GLEAM will need to be tackled. In this presentation, results of these different data assimilation experiments will be summarized, together with the challenges faced to improve land evaporation estimates through data assimilation and potential pathways for future research. [ABSTRACT FROM AUTHOR]

A promising tracer for partitioning the global balance of CO2 is carbonyl sulfide (COS orOCS), a trace gas with shared leaf-level mechanisms to CO2 and H2O. A number of studieshave used COS to derive insights into photosynthesis and transpiration at ecosystem to globalscales. Though it remains unclear whether COS reflects photosynthesis or stomatalconductance most strongly, as its leaf biochemical and physical processes are not perfectlyanalogous to CO2 and H2O. Recent work to characterize COS soil fluxes (e.g., microbialconsumption1 and coupled biological-abiotic emissions2) has advanced our ability to isolateleaf-level information from other ecosystem components. There is a need to evaluate themodels that encapsulate our current understanding of leaf and soil COS fluxes and predictionsof carbon and water cycling against independent constraints in tractable experimentalsystems. Here, we describe a controlled and constrained experimental mesocosm in which fluxesof COS, CO2, and H2O were measured at ecosystem and soil scales and were compared toindependent constraints on carbon and water cycling (i.e., CO2 and H2O isotopes), vegetationdynamics, and soil biological and abiotic properties. Our study system is the miniature replica(1 m2) of the large Landscape Evolution Observatory (LEO) hillslopes (330 m2)housed in the University of Arizona Biosphere 2 infrastructure and filled with 1-mdeep basaltic soil from a bare soil state to a vegetated ecosystem. I will presentthe results of our aims to determine: 1) whether soil COS fluxes are significantand related to soil physical and microbial factors, including carbonic anhydrasegene diversity, 2) how plants and plant-microbe interactions influence COS fluxes,and 3) how well ecosystem-scale COS fluxes track photosynthesis and stomatalconductance. References cited: 1L. K. Meredith, J. Ogée, K. Boye, E. Singer, L. Wingate,C. von Sperber, A. Sengupta,M. Whelan, E. Pang, M. Keiluweit,N. Brüggemann, J. A. Berry, P. V. Welander, Soilexchange rates of COS and CO18O shift with the diversity of microbial communities andtheir carbonic anhydrase enzymes, under review, The ISME Journal 2L. K. Meredith, K. Boye, C. Youngerman, M. Whelan, J. Ogée, J. Sauze, L. Wingate,Coupled biological and abiotic mechanisms driving carbonyl sulfide production insoils, Soil Systems, 2(3), 37. 2018. https://doi.org/10.3390/soilsystems2030037 [ABSTRACT FROM AUTHOR]

Sea Surface Salinity (SSS) is an Essential Climate Variable (ECV) that plays a fundamental role in the density-driven global ocean circulation, the water cycle, and climate. The satellite SSS observation from the Soil Moisture and Ocean Salinity (SMOS), Aquarius, and Soil Moisture Active Passive (SMAP) missions have provided an unprecedented opportunity to map SSS over the global ocean since 2010 at 40-150km scale with a revisit every 2 to 3 days. This observation capability has no historic precedent and has brought new findings concerning the monitoring of SSS variations related with climate variability such as El Niño-Southern Oscillation, Indian Ocean Dipole, and Madden-Julian Oscillation, and the linkages of the ocean with different elements of the water cycle such as evaporation and precipitation and continental runoff. It has enhanced the understanding of various ocean processes such as tropical instability waves, Rossby waves, mesoscale eddies and related salt transport, salinity fronts, hurricane haline wake, river plume variability, cross-shelf exchanges. There are also emerging use of satellite SSS to study ocean biogeochemistry, e.g. linked to air-sea CO2 fluxes.Following the success of the initial oceanographic studies implementing this new variable, the European Space Agency (ESA) funded a new Climate Change Initiative (CCI) SSS project (2018-2020), or simply CCI+SSS project. The CCI+SSS project (2018-2020) aims at generating improved calibrated global SSS fields over 10 years period (2010-2019) from all available satellite L-band radiometer measurements, extended at regional scale to 2002-2019 from C-band radiometer measurements. It will fully exploit the ESA/Earth explorer SMOS mission complemented with SMAP and AQUARIUS satellite missions. The project gathers teams involved in earth observation remote sensing, in the validation of satellite data and in climate variability study. In this presentation we will summarize results obtained during the first year of the project, the contribution of satellite measurements for monitoring SSS and the specific objectives of the CCI-SSS project:- a definition of the requirements for SSS ECV products relevant for the climate studies and consistent with the satellite SSS achievable performances- an harmonization of the SSS products and of the radiative transfer models for a long term consistent and stable SSS time series - a thorough characterization of the uncertainties of the SSS ECV, - an assessment of the ECV product through five case studies related to ocean climate variability and hydrological cycle- Exchange of knowledge between the CCI+SSS team and the international community.The ESA CCI+SSS consortium gathers scientists and engineers from various European research institutes and companies (LOCEAN/IPSL, LOPS, University of Hamburg, NOC, ICM, ARGANS, ACRI-st, ODL) and is conducted in collaboration with US colleagues from NASA and Remote Sensing System. [ABSTRACT FROM AUTHOR]

As an important component of the global climate systems, ocean-continent interaction influences hydrological cycles at regional and local scales. Eastern China is a typical region where oceanic moisture (OM) has significant influences on summer precipitation. Due to its simplicity and accuracy, physical water vapor tracer method based on the stable isotope has been widely employed to estimate the contributions of different sources to precipitation. However, dense and long-term isotopic observations are limited by technical and economic reasons. Isotope-equipped global climate models (iGCMs) provide potential solutions to to improve our knowledge of hydrological processes. Accordingly, this study investigates the potential of using iGCMs to quantify the contributions of the OM to precipitation, which aim at better understanding of the hydrologic cycle processes. A new bias correction method is proposed to correct biases of precipitation isotopes simulated by five iGCMs (i.e. CAM2, GISS-modelE, LMDZ4, MIROC32, and HadAM3). A modified two-component mixing model taking 18O as a tracer is employed to assess the spatiotemporal contributions of summer OM for eastern China. Results show that iGCMs are biased in simulating preciptiation isotopes at local and regional scales. The bias correction method performs reasonable well in terms of reducing the biases. Based on biased-corrected precipitation isoscapes, the influence of OM on summer precipitation is investigated and found that OM plays an important role in summer precipitation, and spatially decreases along the transport route and the passage of time in summer. In addition, the OM contribution to precipitation contain a considerable uncertainty associated with the choice of a given iGCM for each sub-region and sub-period. Overall, bias correction is necessay before applying iGCMs to study hydrological cycles at the regional scale and the application of multi-iGCMs is critical to delineate uncertainty in studying oecanic-land interaction. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is an important water source in Asia. As the "Third Pole" of the Earth, the Tibetan Plateau has significant dynamic and thermal effects on East Asian climate patterns, the Asian monsoon process and atmospheric circulation in the Northern Hemisphere. However, little systematic knowledge is available regarding the changing climate system of the Tibetan Plateau and the mechanisms underlying its impact on third pole region (Tibetan Plateau and the nearby surrounding region). This study was based on "water-cryosphere-atmosphere-biology" multi-sphere interactions, primarily considering global climate change in relation to the Tibetan Plateau –third pole climate system and its mechanisms. This study also analyzed the Tibetan Plateau to clarify global climate change by considering multi-sphere energy and water processes. Additionally, the impacts of climate change in the third pole and the associated impact mechanisms were revealed, and changes in water cycle processes and water conversion mechanisms were studied. The changes in surface thermal anomalies, vegetation, local circulation and the atmospheric heat source on the Tibetan Plateau were studied, specifically, their effects on the East Asian monsoon and energy balance mechanisms. Additionally, the relationships between heating mechanisms and monsoon changes were explored. The research plan and initial progress for the land-atmospheric interaction over the Pan-Third Pole region is shown in the last. [ABSTRACT FROM AUTHOR]

A new Hulu stalagmite was 230Th dated and measured by multi-proxies, including δ18O, δ13C and trace element ratios. A ~10-yr-resolved δ18O record from 51.59 to 42.58 ka provides two new aspects of millennial-centennial oscillations of climate. A highly similar pattern of Dansgaard-Oeschger (DO) cycles as recorded in Greenland ice cores is observed, including the rapid transition (duration <80 yr) and synchronization (difference <35 yr) at the onset of DO-12. Centennial-scale monsoon oscillations during the Greenland interstadials are indicative of the instability of hydroclimate system. After a removal of remote maritime moisture signals from our δ18O record, proportions of water vapor from the short-distance sources increase during cold stadials, thus we propose that the westerly jet plays an important role in controlling the moisture inflow to the East Asia. Furthermore, proxies for cave environmental changes, including δ13C and trace element ratios, display a resemblance to the δ18O record even at centennial scales. This suggests that changes in hydrological processes, soil and vegetation at cave site all have sensitive response to monsoon climates. These findings demonstrate that calcite δ18O at Hulu Cave integrates multiple hydroclimatic processes, thus providing a basis for further interpretation of Chinese cave δ18O. [ABSTRACT FROM AUTHOR]

With the impact of climate change and frequent human activities, especially the hydropower development, the mechanism of runoff yield and flow concentration has changed due to the variability in hydrological cycle and underlying surface of the basin. Observations show that annual runoff had variations during the past several years in Lancang River Basin of southwestern China. Among five sub-basins of the Lancang River Basin, which are determined by five different hydrological stations, namely Changdu, Liutongjiang, Jiajiu, Gongguoqiao and Yunjinghong, the runoff process of Changdu and Yunjinghong have abrupt change points in 1969 and 2004, respectively. In order to analyze major causes for these variations, the hydrological series of these two sub-basins are segmented into sub-series corresponding to different time periods: before and after the abrupt change point. Under this circumstance, the two-parameter water balance model is used to determine the relationship between runoff and precipitation, evaporation and other factors in the two different periods. With the precipitation and evaporation series as input condition, the water balance model parameters which represent the formation conditions of runoff at the same period, are first regulated using the optimization method of human-machine cooperation. Then, according to the simulation of the runoff series in different time periods based on the determined model, factors contributed to runoff changes, including climate change (i.e. precipitation and evaporation) and human activities can be further separated and quantified. Result shows that the contribution rate of human activities changes from 10.94% in Changdu to 64.57% in Yunjinghong, while the contribution rate of climate change varies from 89.06% in Changdu to 35.43% in Yunjinghong. It is consistent with the fact that great dams are mainly constructed in the lower reach of the Langcang River. [ABSTRACT FROM AUTHOR]

Hydrologic and climate models require reliable estimates of evapotranspiration (ET) and its components (E) surface evaporation and (T) plant transpiration for linking the carbon and water cycles and for attribution of water balance and surface fluxes. Some land surface models estimate ET and T using variants of the Penman-Monteith model with empirically-derived expressions for stomatal conductance with E estimated from E=ET-T. We present a method for direct estimation of E based on soil properties and rainfall patterns using the concept of soil evaporation capacitor (SEC). We show that soil type affects surface evaporation by: (1) defining the depth of evaporation effects, (2) controlling the rate of drainage that shelters water from evaporation and (3) determining the resistance to surface evaporation. The SEC is sensitive to local rainfall pattern, soil type and potential evaporation (ET0). Global estimates of E/ET0 vary between 0.05 in dry and hot regions to 0.25 in cool regions and show good agreement with flux tower measurements across soil types and biomes. We capitalize on the remarkably constant ratio T/ET=0.7 found in diverse biomes where vegetation is in equilibrium with local climate (non-agricultural areas) to use soil-based E to estimate annual ET for different regions. Values of climatic ET based on this crude estimate are in remarkable agreement with most advanced global ET product (ERA-interim) highlighting the importance of surface evaporation in determining available soil water for transpiration by vegetation. [ABSTRACT FROM AUTHOR]

Distribution of residence time has been commonly used to characterize the responsecatchment runoff processes. Most previous studies on water residence time have been mainlyfocused on large scale analysis in time and space and on estimating residence timedistribution of total runoff. In this study, we analyzed residence time distribution (RTD) ofdifferent runoff components at event scale in Hydrohill experimental catchment, which islocated in Chuzhou City, Anhui Province, China. Hydrochemical and isotopic data, i.e., 18O,D, anions (HCO3−, Cl−, NO3−, SO42− and F−), cations (K+, Na+, Ca2+ and Mg2+) anddissolved Si in water samples were collected during the rainfall events in 2016, which areused to characterize the response of different runoff components by combining lumpedparameter models. Results showed that 18O and Cl− are the most suitable indicators toevaluate RTD of runoff components. On the experimental catchment scale, groundwaterrunoff gets the longest residence rime among all three runoff components. Residencerime of interflow runoff is approximately 1.38 times longer than that of surfacerunoff. Hydro-chemical tracing provide an effective way to easily measure andunderstanding hydrological processes for critical zone, which could support hydrologicalmodel development by strengthening physical base of hydrological cycle. However,what caused difference in residence time of runoff components and how to quantifyinteraction between different runoff components should be enhanced in furtherstudy. Key words: water residence time; runoff components; lumped parameter models;hydro-chemical and isotopic data; Hydrohill experimental catchment Acknowledgements: The work has been supported by National Natural ScienceFoundation of China (Grant No. 41830863) and National Key Research and DevelopmentPrograms of China (Grant No. 2016YFA0601501) [ABSTRACT FROM AUTHOR]

Billions of people and many ecosystems worldwide are threatened by water crises caused by land conversion, land-use change and other human actions. Understanding how the human water footprint interacts with hydrology at multiple scales is essential for the collective ability of societies to secure water for both people and the environment. For many people, a visualization of the water cycle is the starting point for their understanding of water resources. Even though water cycle diagrams may not be intended as comprehensive and quantitative representations of ecohydrological science, they effectively play that role for many people, including educators and policymakers. This means that systematic inaccuracies in the representation water cycle could compromise efforts to tackle the challenges of water security. Core scientific principles are also implicit in the water cycle, such as the conservation of mass and the possibility of human activity causing global scale changes that have acute local effects. Thus it is important that the content of water cycle visualizations is analyzed and reflected upon. This presentation is based on an analysis of over 450 water cycle diagrams gleaned from both academic and popular sources in 12 different countries. We compared these diagrams to a new estimate of the global water cycle compiled from 50 recent modelling and empirical studies. We found striking biases and misrepresentations in the visualizations, largely independent of their source or age. Particularly striking was the neglect of human interventions in the water cycle as well as distortion in the relative sizes of water pools and fluxes including underrepresentation of the role of the ocean. Depictions of the global water cycle consistently conveyed a false sense of water security, with only 2% of diagrams showing climate change or water pollution—two of the central causes of the global water crisis. These misrepresentations correspond with specific dimensions of water mismanagement, suggesting that flaws in water cycle visualizations reflect and contribute to misunderstanding of global hydrology by both specialists and non-specialists. Integrating human activities into water cycle diagrams is an initial step to communicating a more realistic picture of global water resources and socio-hydrology in the Anthropocene. Hence, we created a revised water cycle diagram that attempts to do this and also address the challenges of accurately visualizing the water cycle. [ABSTRACT FROM AUTHOR]

A complete understanding of hydrology and solute dynamics of tropical humid catchments requires spatio-temporal tracking of fluxes, storage, mixing and flow paths. Additionally, we lack detailed knowledge about how precipitation is partitioned into distinct "green and blue" hydrological processes and their respective transit and residence times. Particularly in the tropics, vegetation plays an important but often underestimated role in hydrological and biogeochemical cycles. If we want to assess future environmental changes on these cycles, we need a better understanding of "green" water fluxes.To this end, we further developed the Spatially-distributed Tracer-Aided Rainfall-Runoff for the tropics (STARRtropics) model to simulate rainforest interception, transpiration, soil water and groundwater fluxes, tracing stable water isotopes throughout the model cascade. The quick runoff response of our system slightly below 1 hour demands high-resolution spatial (10 m) and temporal (1 h) simulations to close the gap between the high-frequency hydrometric and fewer isotope sampling. Data collection within our pristine rainforest experimental catchment (San Lorencito 3.2 km2) in Costa Rica was carried out from Jun 2013 to May 2018. Hydro-meteorological data was registered with 5 min resolution, spatially distributed soil moisture and water samples for isotope analysis were collected on an event-basis if possible, every 15min. Water samples were collected in gross rainfall, throughfall, the main stream and two tributaries. The model was able to reproduce the observed streamflow very well (KGE > 0.8). The average annual streamflow was mostly composed of shallow soil water components (~90%) and the remnant by water from deeper layers. From the total evapotranspiration, the isotope mass balance showed that up to 80% is transpired water. Although this is not surprising in the rainforest ecosystem with high relative humidity above 90% throughout the year and a mostly cloudy sky. Isotope simulations showed a "flashy" response to rainfall in combination with a nearly constant isotope signature from deeper groundwater during baseflow. Simulated stream water age distributions ranged from hours to two years with little older water contributions supporting the notion of a quick responding system with low potential for resilience after more severe changes of the hydrological cycle and precipitation patterns. The water age distributions of interception and transpiration fluxes (hours-weeks) were significantly lower than those of the stream. The stream water ages were a mixture of younger soil (hours-months) and older groundwaters (months-years). Spatially, we detected minor but not negligible age differences between waters originating on the right (old) compared to the left (young) hillslopes of our V-form river valley. Such spatial differences can be directly attributed to a slightly lower slope and resulting deeper soils on the right-hand hillslope.This study shows the value of a high-resolution spatially distributed tracer-aided model with a robust database allowing multi-criteria evaluation of simulations to produce an internally consistent representation of the study catchment. The application of the model helped us to improve our understanding of the hydrological functioning, particularly in terms of temporally and spatially non-stationary water ages in a geomorphologically and biologically complex humid tropical ecosystem. [ABSTRACT FROM AUTHOR]

The Pyrenees range is a transboundary region shared by Spain, France and Andorre. As many other mountain regions, it is exceedntary in water resources that are used in a much larger area that includes important urban concentrations and productive rural areas. This territory is particularly vulnerable to the consequences of climate change. The PIRAGUA project, funded by FEDER through the POCTEFA Programme of the EU, addresses the assessment of the hydrological cycle of the Pyrenees in the context of climate change. The goals of the project are to unify and homogenise the existing information, prospect future scenarios, develop indicators of change, and propose adaptation strategies with impact on the territory, with the ultimate goal of supporting investment aimed at adapting to climate change in relation to water resources. Thus, the project evaluates the components of the hydrological cycle and the water resources of the Pyrenees range in the recent past (1985–2015), and in future scenarios (2030–2050). In addition, it will develop seven case studies about adaptation strategies at the local and regional scales, focusing on different socio-economic sectors, including hydropower production; sensitive headwater ecosystems; water and forests; irrigation agriculture; extreme events; tourism and areas of high ecological value; and multi-sector analysis, including the water-energy connection. [ABSTRACT FROM AUTHOR]

Research on the hydrological cycle at the land surface often focuses on the partitioning ofrainfall into runoff and evapotranspiration by soil and plants. However, between 15 and 30%of rainfall in forested areas does not reach the ground, but is intercepted by canopy surfacesand directly evaporates again. So far, this considerable flux was thought to dependmostly on the total leaf area of vascular vegetation, such as trees. Here, however, weshow that more than a third of global interception is due to non-vascular vegetation,consisting largely of lichens and mosses. Hence, our research highlights a hithertounrecognized impact of non-vascular vegetation on hydrological fluxes in the Earthsystem. To estimate rainfall interception by non-vascular vegetation, we use a process-basednumerical simulation model. A unique property of the model is the explicit simulation offunctional diversity, while most vegetation models reduce diversity to a few plant functionaltypes. This allows for a realistic representation of highly specialised organismssuch as non-vascular epiphytes, and a first estimate of their biomass at the globalscale. Inferred average global water storage capacity including non-vascular vegetation is2.7 mm, which is consistent with field observations and markedly exceeds the values used inland surface models. Consequently, we find that the total evaporation of free water from theforest canopy and soil surface increases by 61% when non-vascular vegetation isincluded. Our results imply that the leaf and stem area of a forest may not be sufficient to predictrainfall interception. Moreover, interception by non-vascular vegetation is likelyto have consequences for regional- to continental-scale hydrologic cycling andclimate. Related publication: https://doi.org/10.1038/s41561-018-0176-7 [ABSTRACT FROM AUTHOR]

The water cycle driven environmental mass load (non-tidal atmospheric / ocean loading and continental water storage loading) induces elastic displacements on Earth surface and gravitational impact on satellite orbits. These non-linear displacements have an impact on the GNSS geodetic stations' locations and on other global geodetic parameters, e.g., Geocenter coordinates, Earth orientation parameters (EOP) and more. We reprocessed 15 years (2000-2014) of GNSS data and generated daily and weekly solutions (consistent with ITRF2014). The GFZ loading models have been applied at the observational level during the analysis. We found that the annual Geocenter signal (over 80% of the x and y components) can be explained by the environmental loading. Variations at the tens of micro-arc-second level of EOP is contributed from loading. The minor influences of the environmental loading displacements at the orbit height is validated and presented. More than 80% of the station coordinate time series benefit from correcting for the environmental loading and show reduced WRMS. [ABSTRACT FROM AUTHOR]

Within the German Science Foundation funded Collaborative Research Center "Earth – Evolution at the dry limit" our overarching goal is to understand the moisture supply to the Atacama desert and its variability which is driven by synoptic and large scale patterns. Characterizing the moisture supply to the Atacama desert in the context of the recent climate is essential in order to establish thresholds for growth and development of the local biota and for surface alternations. Due to the scarcity of in-situ measurements especially over longer time periods, studies on a climatological scale are limited to satellite remote sensing and model data. Here, we extract the integrated water vapor, the divergent water vapor flux, precipitation, cloud heights and cloud cover from model data (ERA-20C), which only assimilates surface observations (pressure and wind), over the course of the 20th century. To assess the quality of these data, comparisons with satellite derived products for recent years and decades are carried out (e.g. water vapor from HOAPS data, cloud heights derived from MISR, and precipitation derived from TRMM). In this extremely dry location situated at the subsiding branch of the Hadley circulation, only very few synoptic features disturb the prevailing dry conditions. These are namely cut-off lows and atmospheric rivers. They are expected to cause an enhanced moisture supply to the Atacama desert. Exploiting the benefits of having an exceptionally long time series of meteorological data, i.e. ERA-20C, we investigate the frequency of occurrence of such features and whether this frequency has changed over the past century. Furthermore, we investigate the moisture supply in relation to El Nino/Southern Oscillation (ENSO) conditions. [ABSTRACT FROM AUTHOR]

In the context of climate change, more severe and extended periods of low flows are expected, which will affect the quantity and quality of water sources. Evapotranspiration is an important process in the water cycle and is particularly significant during low-flow events. Therefore, it is important to study the effects of uncertainty in evapotranspiration modelling in the hydroclimatic modelling chain to understand the impacts of climate change on the water availability. As evapotranspiration is a rather hard and expensive process to measure, formulas are used to determine potential evapotranspiration (PET), which is the maximum water quantity that can be evaporated and transpired without any limiting factors. The objective is to determine the contribution of PET formulas to uncertainty in the full modelling chain in the context of climate change. Eleven simple PET formulas that only require minimum and maximum temperatures as well as the latitude are used. These formulas are applied to 2080 watersheds in North America (235 in Canada, 1825 in United States, and 20 in Mexico). As PET is directly related to climatic conditions, studying a large quantity of watersheds that cover many climatic zones increases the robustness of the conclusions. Three global hydrological models (GR4J, HMETS and Mohyse) calibrated with the Nash-Sutcliffe criterion are employed for the hydrologic modelling aspect of the work. Subsequently, the study of transferability under future climate is conducted with simulations from ten climate models and two different greenhouse gas emission scenarios. These simulations outputs (precipitations and temperatures) are post processed with two bias correction methods and are then introduced into the three hydrological models. The PET contribution in the global modelling chain in climate change and its uncertainty are estimated with different analyses such as variance decomposition. The analysis of different low-flow indices allows studying the climate change trends as expressed through the PET formulas. For instance, low-flow values over a period of several consecutive days for a certain recurrence period are compared to see if changes in the PET affect low-flows. Results show that the PET increases and the low-flow decreases are different according to climatic zones. Despite a great variability between the different formulas, results show similar trends under climate change. This project also shows that some specific formulas do not adapt well to future climate. This project results in a better comprehension and an increase in knowledge regarding the impacts of the PET formula choice in hydroclimatic modelling chain under climate change. The conclusions can be used for water resources management to identify adequate adaptation measures, such as preventing the drying up of water resources during low-flow periods. [ABSTRACT FROM AUTHOR]

The hydrological cycle is a fundamental component of the Earth&#x2019;s climate system. Modelingthe time response of this cycle and the implied physical processes challenges thegeneral circulation models (GCM) used to study the climate system and to projectfuture climate. Water stable isotopes (H216O, H218O and HD16O) are integratedtracers of climate processes occurring in various branches of the hydrological cycle.Changes of the isotopic composition, which can be measured in various naturalclimate archives, have been used, for example, to reconstruct past temperatureschanges at high resolution or to study the past dynamics of the monsoon. However, thequantitative translations of isotope signals recorded in the natural archives to climatevariables is still challenging. The explicit modeling of these isotopes in GCMs isone way to improve our understanding of the mechanisms controlling the waterisotopes distribution link with the variations of climate and to evaluate the modelperformance. We present here the results, under pre-industrial (PI) and mid-Holocene (6k) conditions,of the new isotope-enhanced version of the fully coupled Earth system model MPI-ESM,called hereafter MPI-ESM-wiso. For that, the water isotopes have been implementedin all the components of the model (ECHAM6: atmosphere, JSBACH: dynamicvegetation, MPIOM: ocean/sea-ice). The related isotope masses of H216O, H218Oand HD16O are exchanged between the atmosphere and the ocean via the couplerOASIS3. The mid-Holocene, one of the PMIP4-CMIP6 entry cards to evaluate theperformance of the coupled GCMs [1], provides the opportunity to evaluate the modelresponse to changes in the seasonal and latitudinal distribution of insolation induced bydifferent orbital forcing conditions. Especially, this period is characterized by enhancedAfrican and Indian monsoons with depleted isotopic contents of precipitation. Inaddition to classical variables (temperatures, precipitation amount...), we evaluatethe isotopic composition of precipitation, water vapor, ocean, etc. simulated byMPI-ESM-wiso against available observations. We also investigate the variability of theisotope-to-climate gradients (spatial and temporal) during and between the PI and 6kperiods. This work will be an important contribution to the Paleoclimate ModellingIntercomparison Project. Indeed, the models with an explicit water stable isotope diagnosticsmake it possible to perform direct comparisons, at different time periods, with environmentalrecords and to reduce the uncertainties resulting from the interpretation of these records interms of climate signals in model-data comparisons. The project is part of the PalModinitiative ("Paleo Modelling: A national paleo climate modelling initiative"), funded by theGerman Federal Ministry of Education and Science (BMBF). [1] Kageyama et al., Geosci. Model Dev., 11, 1033-1057, 2018. [ABSTRACT FROM AUTHOR]

Numerical simulations of rainfall-runoff processes are valuable tools for understanding hydrological processes and for assessing the impact of certain decisions on the hydrological cycle of the study areas. The advancements in the computer technology and data acquisition have assisted their rapid development and wide use. The current research aims at evaluating the applicability of the physically-based, fully distributed model TOPographic Kinematic APproximation and Integration TOPKAPI-eX for the simulation of flood events in two sub-catchments in Saxony State, Germany. This model has not been applied for German watersheds with high spatial resolution data. The results indicate that the model is calibrated well for the Wernersbach sub-catchment (Nash Sutcliffe Efficiency coefficient-0.89), whereas for the Wesenitz sub-catchment it was only satisfactory (NSE-0.7). As the model uses two soil layers, the addition of the second soil layer has improved the model performance in comparison to the simulations with only one soil layer in the case of the Wernersbach sub-catchment (NSE increase from 0.83 to 0.89). During the validation process, the model performance has shown variable results for both catchments. The best performance was achieved for the Wernersbach sub-catchment for the year with the highest flow (NSE-0.95) in the last decade. The lowest performance coefficients for Wernersbach and Wesenitz sub-catchments were 0.64 and 0.64, respectively. The reasons for low model performance were discussed to be: low data quality and data insufficiency, methods used during the simulations are interpolations, manual calibration, ETP estimation, etc., and the assumptions made during the calibration. [ABSTRACT FROM AUTHOR]

Many recent studies indicate climate change as a phenomenon that can potentially alter the water cycle, also implying new challenges in drought risk management. Impacts of drought are difficult to study, as this phenomenon is usually characterized by multiannual evolution scales, meaning that few occurrences may take place in a climatologic period of 30-years. Hence, it is of key importance to assess the quality of Regional climate models (RCMs), which are commonly used for assessing future impacts of climate change on hydrological events. To this end, a common approach consists in evaluating models' capability to simulate historic climate by comparing models' simulations to observational gridded datasets, available at global or continental spatial scales. Regardless of the specific methods used to assess the differences between simulated and observed data, a main limitation in this approach is that the considered spatial resolution is too coarse for reliable climate change impact studies at hydrologically relevant scales, especially in areas of complex topography. From this point of view, large scale observational gridded datasets are of poor applicability, since they are built upon low-density hydro-meteorological networks.The Coordinated Regional Climate Downscaling Experiment (CORDEX) initiative provides climate data simulated by RCMs developed by several research centers all over the world. In the present study we use climate data for the Euro-Mediterranean area, known as EURO-CORDEX (www.euro-cordex.net). In particular, simulations for an historic reference period (baseline) and for future projections up to 2100, with a 12.5 km grid resolution, are available for four different greenhouse gas concentration trajectories (Representative Concentration Pathways). We propose a statistical methodological framework to assess the quality of the EURO-CORDEX RCMs with respect to their ability to simulate historic climate by a comparison with high-density and high-quality ground-based observational datasets. In particular, the focus of this study is on observed thermometric and pluviometric regimes in Southern Italy at time scales from monthly to annual, which are particularly useful for drought analyses. To this aim, performances indicators relevant for assessing the accuracy of assessments are also considered. The proposed methodology is applied to Sicily and Calabria regions, where long historical precipitation and temperature series have been recorded by the ground-based networks operated by the formerly Regional Hydrographic Offices, whose density is considerably greater than observational gridded datasets available at European level, such as E-OBS. Results show that the proposed methodology is capable to highlight clearly skills and weaknesses of different RCMs and can help to properly select the models for climate projections in the investigated areas, with respect to the examined hydrologic processes. [ABSTRACT FROM AUTHOR]

The water cycle is not only a generator of ecosystem services and a critical driver of Earth system change. It is also a system subject to intense human interferences. Hydropower development is well known to modify the amount and variability of discharge in river streams around the world. Furthermore, there is growing evidence of impacts of reservoir impoundment and flow regulation on other hydroclimatic variables such as potential and actual evapotranspiration, convective energy and soil moisture. In this study, we performed a trend analysis of several hydrological variables based on the Budyko framework in a 1,630 -km² hydrological basin in Central Colombia and two of its upstream subbasins. Our aim was to detect any possible hydroclimatic effect of the impoundment of the Prado Reservoir within the Prado River hydrological basin. The hydroelectric project comprises a single reservoir with an installed capacity of 1,1 x 106 m³ and a hydroelectric station that came into operation in 1973. We gathered monthly observed data for precipitation, temperature, radiation and runoff and used it to calculate initially potential and actual evapotranspiration, the aridity index and the evaporative ratio during the period of 1952-2014. We calculated change before and after the construction of the dam for all these variables, and a running coefficient of variation (CV) for both precipitation and runoff, and used statistical tests such as Pettitt and Wilcoxon significance tests to identify changes in the trend series. We found that after the commissioning of the project, precipitation and runoff simultaneously decreased in all basins. The changes in variation and magnitude of the CV of runoff in the downstream station reflected the effects of regulation, effect not observed in the subbasins upstream of the project. On the contrary, no effect of the reservoir was found on basin-scale evapotranspiration, as it has been found in other heavily regulated basins worldwide: after performing a separation technique on evapotranspiration change, we found that the residual change in evapotranspiration not related to climate variability, and attributed to other factors, was negligible. This may be explained by the fact that the construction of only one reservoir within the hydrological basin may not be sufficient to evidence an effect on net evapotranspiration from flow regulation from the entire basin. [ABSTRACT FROM AUTHOR]

Soil moisture plays a key role in the water and energy cycle through the evaporation andrainfall over land. In complex topography regions such as South Asia and West Africa therole of the soil moisture in modulating local rainfall becomes more vital, which is analyzed inthe current study for the summer (June-September; JJAS) season. We obtained soil moistureGlobal Land Data Assimilation System (GLDAS) dataset for the period 2000-17, which ishigh resolution (0.25 deg) at global grids. We noticed that the MAY soil moisture variabilityin the tropical western African region is important for the successive JJAS rainfalllocally and as well as remotely for the South Asian region. The linear relationshipbetween one-month lead (MAY) soil moisture and JJAS rainfall shows that dryconditions may prevail in the western Africa for dry Soil moisture conditions andsimilar is notice remotely for the South Asian region. The relationship of SMAIand monsoon rainfall becomes more significant if we remove El Niño SouthernOscillation (ENSO) affect from SMAI. The mechanism and physical links between theantecedent soil moisture and successive rainfall are illustrated using Moist Static Energy(MSE). MSE and soil moisture have the similar anomaly composites for May andJune-September as dry and wet. Other than MSE the Potential Evapotranspiration (PET)is in good agreement in terms of anomaly with soil moisture anomaly both forWest Africa and South Asia. We also used REGgional Climate Model (RegCM)for a case study of 2007 flood case happened West Africa by using 10-ensemblemembers based on time lag approach. We found that that May soil initialization isimportant for the improvement of the extreme events. Please fill in your abstract text. [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) is a key process in the hydrological cycle. However the understanding and predicting of water balance changes due to land use and climate change is complex because of the poor representation of ET in most models and sparse observations. In this contribution, I will discuss how different ET observations from have provided important insight into: a)~the sensitivity of ET to soil moisture (Teuling et al., 2006), b)~consistency in ET estimates over contrasting land cover (Teuling et al., 2018), c)~the response of energy balance partitioning over different ecosystems to heatwaves (Teuling et al., 2010), d)~the contribution of ET anomalies to storage anomalies during drought (Teuling et al., 2013), and e)~the control of land use and vegetation properties on large-scale water balance partitioning (Teuling et al., 2019) and sap flow (Hoek van Dijke et al. 2019). In many cases, these insights conflict with assumptions behind current modelling approaches. It will be argued that ET observations across a range of scales and techniques are needed to drive scientific discovery and improve current modelling approaches.\textbf{References}Teuling, A.~J.; S.~I.\ Seneviratne; C.\ Williams \& P.~A.\ Troch (2006), Observed timescales of evapotranspiration response to soil moisture. \textit{Geophysical Research Letters}, \textbf{33}(23), L23403, \url{http://doi.org/10.1029/2006GL028178}.Teuling, A.~J.; S.~I.\ Seneviratne; R.\ St\"ockli; M.\ Reichstein; E.\ Moors; P.\ Ciais; S.\ Luyssaert; B.\ van den Hurk; C.\ Ammann; C.\ Bernhofer; E.\ Dellwik; D.\ Gianelle; B.\ Gielen; T.\ Gr\"unwald; K.\ Klumpp; L.\ Montagnani; C.\ Moureaux; M.\ Sottocornola \& G.\ Wohlfahrt (2010), Contrasting response of European forest and grassland energy exchange to heatwaves. \textit{Nature Geoscience}, \textbf{3}(10), 722--727, \url{https://doi.org/10.1038/ngeo950}.Teuling, A.~J.; A.~F.\ Van Loon; S.~I.\ Seneviratne; I.\ Lehner; M.\ Aubinet; B.\ Heinesch; C.\ Bernhofer; T.\ Gr\"unwald; H.\ Prasse \& U.\ Spank (2013), Evapotranspiration amplifies European summer drought. \textit{Geophysical Research Letters}, \textbf{40}(10), 2071--2075, \url{http://doi.org/10.1002/grl.50495}.Teuling, A.~J. (2018), A forest evaporation paradox investigated using lysimeter data. \textit{Vadose Zone Journal}, \textbf{17}, 170031, \url{http://doi.org/10.2136/vzj2017.01.0031}.Teuling, A.~J.; E.\ de Badts; F.~A.\ Jansen; R.\ Fuchs; J.\ Buitink; A.~J.\ Hoek van Dijke\index{Hoek van Dijke, A.~J.} \& S.\ Sterling\index{Sterling, S.}. Climate change, re-/afforestation, and urbanisation impacts on evapotranspiration and streamflow in Europe. \textit{Hydrology and Earth System Sciences}, under review, 2019.Hoek van Dijke, A.~J.; K.\ Mallick; A.~J.\ Teuling; M.\ Schlerf; M.\ Machwitz; S.~K.\ Hassler; T.\ Blume \& M.\ Herold. Does NDVI explain spatial and temporal variability in sap velocity in temperate forest ecosystems?, \textit{Hydrology and Earth System Sciences}, under review, 2019. [ABSTRACT FROM AUTHOR]

The quantification of aquifer contribution to river discharge is of primary importance toevaluate the impact of climatic and anthropogenic stresses on the availability of waterresources. Several baseflow estimation methods require river discharge measurements, whichcan be difficult to obtain at high spatio-temporal resolution for large basins. The SWOTsatellite mission will provide water level values from which discharge estimations will bederived for large rivers (&#x003E; 50 - 100 m wide) even in ungauged basins with a maximumfrequency of 21 days. We develop a methodology to estimate baseflow over a whole mission lifetime. To thisaim, an algorithm based on hydrograph separation using the Chapman&#x2019;s filter was developedto automatically estimate the baseflow in a river network at regional scale (&#x003E; 10 000 km2).The algorithm was applied to the Seine River basin (75 000 km2, France) using the dischargetime series simulated at daily time step by the coupled hydrological-hydrogeological modelCaWaQS to obtain the reference baseflow estimations. The same algorithm is then forcedwith discharge time series sampled at SWOT observation frequency. The average baseflow isestimated with good accuracy for all the reaches which are observed at least once per cycle(relative bias less than 8 %). The time evolution of baseflow is also rather wellretrieved, with a Nash-Sutcliffe coefficient above 0.7 for 96 % of the network length(Baratelli et al., 2018). Based on former estimations of uncertainties on dischargesthat will be estimate by the mission, it appears that baseflow estimates are alwaysslightly lower than those on discharge. This work provides new potential for thehydrological community to better close the water cycle using forthcoming spacebornedata. Reference : Baratelli, F., Flipo, N., Rivière, A., Biancamaria, S. (2018) Retrieving riverbaseflow from SWOT spaceborne mission, Remote Sensing of Environment, 218, 44-54.doi:10.1016/j.rse.2018.09.013 [ABSTRACT FROM AUTHOR]

The Cordillera Barroso in Southern Peru (17°50'S 70°45'W, 1750 – 5500 m a.s.l.), lost its glacier coverage completely in recent years. However, solid precipitation and related snow cover still play an important role in the hydrological cycle and the water supply for the three Peruvian Regions Moquegua, Puno and Tacna located in this zone. Therefore, the aim of the research was to assess the snow cover duration and its seasonal variability for the years 2015 to 2017. Snow cover in this mountain range was analyzed using Level 3 products (MOD10A2 – Snow Cover Extent) obtained by the MODIS sensor onboard the Terra satellite. This data has been processed with GIS and remote sensing tools and software. Obtained results were then compared to climatic data from Peru's Meteorological and Hydrological Service (SENAMHI). Later, statistical correlation and tendency tests were applied in order to analyze the distribution and persistence of the snow cover. Results indicate that the persistence of the snow cover in the Cordillera Barroso is about 80% over the three years of analysis. Snow accumulation is higher between January and March (austral summer) and lower between June and August (austral winter). During the dry period (May – August), snow cover is smaller and the persistence of the snow cover reaches 80%. During the wet season (September – April) the snow cover is larger with a persistence of 82%.Interannual variation is not significant, but in 2016 a slight reduction of the snow cover persistence was registered due to the effects of the El Niño event. Strongest accumulation appeared between 4250 and 4750 m a.s.l., with a higher persistence (>80%) above 4750 m a.s.l. When applying the Mann-Kendall test for the snow cover dynamics assessment, no tendency was detected. This indicates that snow cover does not behave in a linear manner, increasing and decreasing as a function of time, but rather depends on atmospheric conditions, as pointed out by the linear Pearson correlation tests between de dependent variable (snow cover) and the independent variable (climatic data). [ABSTRACT FROM AUTHOR]

Identifying the components contributing to the sensitivity and resilience of water resources constitutes a research priority of global relevance. Here we present a practical approach to globally assess the hydrologic sensitivity of regions to climate variability. The aim is to identify the regions most vulnerable to changes in their hydrologic functioning as they experience external climatic shifts. For this purpose we present a new metric, the Hydrologic Sensitivity Index (HSI). HSI is calculated for any given location within 50 degrees North and South of the equator using annual values of Potential and Actual Evapotranspiration (PET and AET) obtained from the Moderate Resolution Imaging Spectrometer (MODIS), and Precipitation (P) from the Tropical Rainfall Measuring Mission (TRMM) for all continents for the last 16 years (2001-2016). The HSI defines the hydrologic behavior under a given climatic condition by calculating the change in the Evaporative Index (DAET/P) against the change in the Dryness Index (DPET/P) between consecutive years. For HSI values ≥1, regions are classified as Sensitive and for values of <1, Resilient. We calculated the mean, frequency and intensity of the HSI and analyzed the distribution of sensitive areas (HSI ≥1) against changes in latitude, elevation, slope and aspect conditions using a 90m elevation dataset from the Shuttle Radar Topography Mission (STRM), as well as according to land cover properties defined by different biome types. Our analysis show the most hydrologically sensitive regions to climate variability occur in Temperate Grasslands along the Great Plains in North American and the Great Dividing Range in Australia, in parts of eastern China, in European Temperate Forests, parts of Tropical and Subtropical pampas east of the Amazonian forest and Tropical and Subtropical African Savannas. We also observe a combined latitudinal-elevation control on the HSI that is particularly noticeable along equatorial regions of the globe. [ABSTRACT FROM AUTHOR]

Taiwan is a mountainous island and two-thirds of the area occupied by mountains. To be an alternative water source for emergent use in drought, the groundwater in the mountain area should be widely investigated. However, the hydrogeological unit in mountain area is mainly composed of fractured hard rock. Both of conductance and storativity are difficult to be estimated. In addition, the hydrogeological system is complicated by geological structures, such as fold and fault. The investigation is very costly and the government has been proceeding systematically for years in Taiwan. The current work is a part of the plan. In this study, the spatial distribution of low permeable formation and geological structure were firstly determined for subdividing Dajia River in Central Taiwan into four groundwater watersheds. To focus on the one located at the central area, the hydrological and climatic information were subsequently collected for establishing the seasonal hydrological cycle in the watershed. In addition, spectrum analyses including Fast Fourier transform and cross correlation were applied to the stream flow data for evaluating the baseflow. The hydrogeological properties were estimated with pumping tests on six 100-meter-deep wells. The hydrochemistry of river water, seepage, springs and groundwater can also demonstrate the water-rock interaction, which implies the groundwater flow path and residence time. However, the temporal and spatial distribution of groundwater water level is one of the most important information, which can evaluate the groundwater flow across the hydrogeological divide. The satellite imagery and field survey are utilized to establish a database of groundwater water level in the study area and machine learning will be helpful to construct a model among the data of topography, climatology, hydrology and hydrogeology. [ABSTRACT FROM AUTHOR]

Observed Influence of SST on the Tropical Atmospheric Water CycleAbstractThe objective of this paper is to improve our understanding of the relationships between the atmospheric water cycle variables, using a new synergistic data set of instantaneous spaceborne observations. This data set consists of five years (May 2012 to April 2016) of relative humidity profiles from the Megha-Tropiques satellite, collocated with cloud and precipitation from the CALIPSO and CloudSat satellites. The data is gridded on a 1° × 1° spatial resolution, collocated once daily (1.30 pm LT) and partitioned into atmospheric circulation regimes, as well as cloud phase and opacity categories and precipitating/non-precipitating scenes. The results show that all SST bins are dominated by non-precipitating cloud objects, but highlight that convective precipitation only occurs for SSTs above 299 K, whilst stratiform precipitation from liquid clouds can be present down to 291 K. In extreme ascending situations, when the atmosphere contains an ice cloud (dominant mode: 72 %), different behaviors are seen below and above the 299 K SST threshold – often referred to and discussed in several previous papers as the threshold for the onset of deep convection and/or a runaway greenhouse effect: (i) Below 299 K, the atmosphere is fully overcast with opaque clouds, whilst above 299 K, the opaque cover decreases and favors more thin clouds. (ii) As the SST passes over the 299 K threshold, the moist RH rises from the near-surface layer to the free troposphere. (iii) In the mid-troposphere, precipitating scenes are moister than its non-precipitating counterparts, but drier in the PBL and at the tropopause level. Further discussions will treat the contrasts between extreme ascending and descending regimes, under which conditions the different sub regimes dominate, as well as the signature of the El Niño period and its impact on the relationships between the atmospheric water cycle variables. [ABSTRACT FROM AUTHOR]

Environmental models are common tools to simulate fluxes and states within the terrestrial energy and water cycles. Simulation results serve a wide range of purposes from infrastructure planning to weather forecasting. Regardless of the purpose, it is a common task to accurately estimate parameters within the process formulations used in environmental models for each computational unit (i.e., grid cell). The dimensionality of the parameter space is equal to the number of parameters per grid cell times the number of grid cells in distributed large-domain modelling, such as in weather forecasting. Without proper regularization of the parameter space, it is impossible to efficiently estimate parameters in this case. One regularization approach is to estimate constant parameters across the modelling domain, but this does not make use of high-resolution data that is available today (i.e., soil maps and land cover information). The Multiscale Parameter Regionalization (MPR) is a promising alternative that makes use of exactly these data sets.The multiscale parameter regionalization (MPR) translates local land surface properties into model parameters. It consists of two steps: first, it relates local geophysical data sets (e.g., soil maps) to high-resolution model parameters via transfer functions at the native resolution of the input data sets. Second, it upscales the high-resolution model parameters to the modeling scale (i.e., the scale at which the model has been applied). MPR has been introduced in the mesoscale hydrologic model (mHM, Samaniego et al. 2010, Kumar et al. 2013), but has recently been made available as a stand-alone tool.In this study, we use the stand-alone tool of MPR to apply it to the land-surface model HTESSEL. This model is the land-surface component of the ECMWF seasonal forecasting system. It uses a tiling approach to differentiate between different land cover types (e.g., high-grown vegetation and shrubs) and assumes constant parameters for each type. Soil related parameters are also considered for few soil classes for the entire domain. While this covers a large extent of subgrid variability at coarse resolutions, we find that its effect at high resolutions is reduced. In this study, we apply MPR for soil water parameters (e.g., conductivity and porosity) and vegetation parameters (e.g., stomatal conductance) that were identified as sensitive in Orth et al. (2016). We find that MPR provides more accurate fluxes over Europe across different resolutions than constant parameters in HTESSEL because it considers the subgrid variability of parameters. We also find a reduced difference between fluxes estimated at different resolutions by applying MPR (i.e., improved flux-matching).References:Samaniego L., et al. https://doi.org/10.1029/2008WR007327Kumar, R., et al. https://doi.org/10.1029/2012WR012195Orth R., et al. http://journals.ametsoc.org/doi/abs/10.1175/MWR-D-15-0283.1 [ABSTRACT FROM AUTHOR]

Evapotranspiration has a large impact on water budgets, playing a fundamental role in theregulation of water fluxes between soil, vegetation and atmosphere. In forested catchments,the evapotranspiration is dominated by the transpiration component. Despite its importantrole in the hydrological cycle at the catchment scale, transpiration is often overlooked and notwell represented by hydrological models. In this work, we aim to investigate the role of evapotranspiration on the hydrologicalresponse and the water balance of two small forested catchments in Italy: the Ressi catchment(0.02 km2) located in the pre-Alps, and the Re della Pietra catchment (2.0 km2) in theApennines. The two catchments are covered by dense mixed broad-leaf forest, but the Ressicatchment is characterized by wetter conditions than the Re della Pietra catchment due to thelarger mean annual precipitation. Meteorological (rainfall, air temperature, global solar radiation and wind speed), soilmoisture and leaf area index data were collected in the two catchments, and these data wereused to perform hydrological simulations with the GEOframe-NewAGE system. Then, thepredicted streamflow was compared to the measured streamflow data at the two streamgauging stations. The modular structure of the hydrological model allowed for testingdifferent methods to compute hourly evapotranspiration amounts, i.e. classical approachessuch as the Penman-Monteith FAO method, the Priestley-Taylor equation and the newSchymanski-Or method, which was modified to include the water stress factor andtranspiration resistances. The Schymanski-Or method was also upscaled from the leaf to thecatchment scale. Preliminary simulations performed with the different methods to estimate evapotranspirationwere evaluated using the Nash-Sutcliffe and the Kling-Gupta efficiency, showing generallybetter results using the Schymanski-Or method. Further analyses will be carried out tocompare the evapotranspiration fluxes and the hydrological response in the two catchments atdifferent time scales. Acknowledgements: This study is part of the research project "SILVA - Water fluxesbetween soil, vegetation and atmosphere: a comparative analysis in two Italian forestedcatchments", funded by Premio Florisa Melone 2018 assigned by the Italian HydrologicalSociety. Keywords: evapotranspiration, forested catchments, hydrological model,GEOframe-NewAGE. [ABSTRACT FROM AUTHOR]

The applied science community continues to expand the science outcomes from satellite missions. This group is an important and growing focus of international space agencies wishing to inform and educate existing and potential users of data from satellite missions. The cost of developing, launching and operating these missions is large, but the high value of the data and information products that result provide a rich resource for operational agencies, commercial interests, as well as for the research community. More than twenty-six years of time series data from a suite of ocean altimetry missions, beginning with TOPEX/Poseidon and continuing through the Jason-series, have facilitated broad utility of the data, which demonstrates the high value of the science and data/information products derived from these missions to address societal needs. Societal benefit areas include safety, commercial and operational interests, and decision-making. Future planned missions, such as Jason-CS/Sentinel-6A and B, and the Surface Water and Ocean Topography (SWOT) mission, will extend the value and applications potential of mission data even further. In particular, a broad range of applications derived from the science and engineering advances of novel technologies developed for SWOT, and the resulting data and information products that come from it, are anticipated.The ocean altimetry missions, and the hydrology applications from SWOT, will continue international partnerships between the U.S. and European space agencies. The expanding time series of measurements of changes in these ocean and surface water bodies will continue to allow scientists and operational users to monitor the hydrologic cycle, flooding, small scale features of ocean circulation, and the climate impacts of a changing environment. In coastal regions, it is anticipated that SWOT surface water measurements may inform a broad range of applications in support of coastal and estuarine managers, marine operators, and decision makers interested in offshore conditions and the ocean state relevant to their regions. NASA's Physical Oceanography Distributed Active Archive (PO.DAAC) is a key component of the success of these missions, by making data products discoverable, accessible, and useful to a broad user community. Efforts to better understand the needs of a diverse user base, and to provide improved user engagement and access to data, information products, and training are being developed by PO.DAAC, and will offer practical and enhanced options to both science research and applications users. This includes an effort to provide data through a Cloud computing environment, which is expected to support big data analytics and expand the use of the ever-growning amount of remotely sensed earth science data. [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) are important phenomena delivering ~90% of poleward water vapor transport to midlatitudes and associated with hydrological extremes being dense distributed spatially. They are associated with strong precipitations along western mid-latitude continental coastlines and can cause flooding events or droughts relief. Understanding ARs role in the global hydrological cycle is critically important for assessment and prediction of regional precipitation extremes.Modern reanalyses, climate models outputs and regional downscaling products are a very good source of data for development numerical tools for ARs identification, tracking, and analysis of atmospheric rivers.A number of atmospheric rivers identification tools have been developed to date, the ARTMIP (Atmospheric River Tracking Method Intercomparison Project) has been started a few years ago. However, the main problem of the ARs tracking methods so far is to subset spatial grid points which are associated with ARs. Most of the developed algorithms rely on sets of conditional rules filtering grid points and resulting in a set of nonconvex regions that are AR-candidates. These regions are then filtered with a set of rules. Most of existing global AR detection schemes differ in spatial grid points subsetting and AR-candidates filtering algorithms.We present the novel combination of algorithms that allow detecting ARs accurately. The gridpoints subsetting algorithm allows selecting AR-candidates taking into account multidecadal integrated vapor transport statistical characteristics. We also present the novel AR-candidates filtering algorithm based on the accurate estimation of the geometric characteristics of AR-candidate regions. One of our most novel approaches is the usage of neural networks methods for tracking of the ARs through the lifecycle. With this set of algorithms, we have detected and made an attempt to track ARs in MERRA2 and ERA-Interim reanalyses, CMIP5 high-resolution model experiments and some regional downscaling products. We present preliminary global climatologies of ARs based on these data. We also demonstrate the comparison of reanalyses and CMIP5 model experiments in the scope of ARs activity and water transport induced by them.This research was supported by the Russian Ministry of Education and Science (agreement 14.613.21.0083, project ID RFMEFI61317X0083) [ABSTRACT FROM AUTHOR]

Climate impact of the Atlantic Multidecadal Variability (AMV) on the Northern Eurasia is poorly documented in literature due to the lack of observations in space, limited by the local fighting weather conditions, and in time, i.e. the analysed timescale is too long compared to the observational record (~120 years). To overcome this limitation, an idealized modelling approach designed in CMIP6 Decadal Climate Prediction Project is applied, based on the CMCC-CM2-SR5 coupled model: the North Atlantic sea surface temperature are continuously nudged towards the positive (negative) AMV anomalies to simulate the warm (cold) AMV phase. An ensemble of 32 members is performed for each experiment, in which all the forcings are set at the pre-industrial values for a 10-year integration time.Model results shows that, during Boreal summer, a positive phase of the AMV induces a circumglobal east-west wave train across the entire Northern Hemisphere. Enhanced westerly winds alters the climatological upper-troposphere circulation, advecting moisture from the North Atlantic Ocean along the northern part of the Eurasian continent. In particular, over Siberia, an anomalous geopotential dipole promotes the poleward movement of specific humidity from the Pacific Ocean, converging at high latitudes with the aforementioned westerly flux. Moisture anomalies regionally contribute to May-to-August rainfall, intensifying multidecadal precipitation over Scandinavia and Eastern Russia. Interestingly, rainfall rises by 10% of its climatology over Siberia, where the AMV-induced moisture fluxes converges.Furthermore, this study also points out that the AMV has a role in modulating the freshwater balance of the Arctic Ocean, due to the anomalous precipitation over the Siberian rivers' watersheds (Ob', Yenisei and Lena). Siberia is a key region for the hydrological cycle of the Arctic Ocean and the catchment areas of these three large rivers accounts for about 46% of the Arctic freshwater input provided by terrestrial sources. We find a decrease of sea surface salinity (about 12% of model climatology, broadly consistent with the anomalous river discharge) in the proximity of the river mouths during positive-AMV years.These results disclose the potential predictability of precipitation over northern Eurasian via tropical-extratropical pathway, associated with multidecadal fluctuations of the North Atlantic sea surface temperatures, in agreement with recent observational studies.This work is supported by EUCP (European Climate Prediction system) under Horizon 2020, grant agreement 776613. [ABSTRACT FROM AUTHOR]

Terrestrial geologic deposits preserve information on the sign, magnitude and spatial heterogeneity of past changes in the water cycle. Reconstructing these changes requires constraining both moisture delivery (precipitation) and removal (evapotranspiration and runoff) from a landscape. Energy fluxes, through the partitioning of sensible and latent heating, play a crucial role in these water cycle dynamics. Here, we illustrate how the energy budget refines the solution space of past water cycle changes. By linking this mechanistic modeling approach with geologic observations, we can develop meaningful predictions of hydroclimate change from regional to global scales.In this contribution we reconstruct water availability in mid- to high-latitude regions using two approaches that incorporate energetic constraints. First, to illustrate the utility of these approaches at a regional scale, we use lake area scaling relationships with Budyko curve constraints to forward model the size and spatial distribution of lakes in endorheic basins. We focus here on forward modeling Cenozoic water availability in western North America. In doing so we predict that warmer-than-present periods, such as the Eocene and mid-Pliocene, would have required substantial increases in precipitation to supply sufficient water to develop large lake systems in the now-arid continental interior. Second, at a global scale, we incorporate changes in albedo (due to for example, vegetation changes and ice sheet growth), as well as changes in continental configuration, into a moist energy balance model of the hydrologic cycle. Applying these parameterizations to Phanerozoic paleogeographic changes, we make first-order temporal predictions for changes in continental runoff, and discuss implications of these results for terrestrial water storage and silicate weathering over geologic time. [ABSTRACT FROM AUTHOR]

In mid-Holocene (ca. 6,000 years ago) different orbital conditions caused more summer insolation in the Northern Hemisphere than at present-day. This had lead to a dramatic increase in the vegetation cover in North Africa and a strengthening of the West African Monsoon (WAM). Since the Sahara was mainly covered by grassland and savanna, the atmospheric burden of Saharan dust was substantially lower than today. It is typically difficult to fully reproduce the WAM behaviours in mid-Holocene from proxy reconstructions with climate models, if they do not account for accurate changes in vegetation and dust aerosol. While many models have implemented interactive vegetation in Earth System Models, dust aerosol is often prescribed with a climatology and not interactively calculated in paleo-simulations, e.g., due to the computationally expensive aerosol schemes. Here, we present results from mid-Holocene simulations performed with the Max Planck Institute Earth System Model (MPI-ESM). The prescribed distribution of dust aerosol and its optical properties are derived from an aerosol-climate simulation with ECHAM6-HAM (Egerer et al., 2016), that has the same atmospheric model as MPI-ESM. Our results show that accounting for Saharan dust reduction substantially warms mid-Holocene summers both locally in the Sahara and even globally, with a global mean warming of about +1.2 K relative to the control simulation, based on pre-industrial dust. The regional hydrological cycle changes substantially. Evaporation increases in the region between 10°N - 20°N of the ascending branch of the Hadley circulation, leading to a dramatic change in the P-E balance there. The net effect of this response is an about 14% weaker and narrower WAM compared to the simulation with the pre-industrial dust aerosol. These changes are an improvement of the model performance in comparison to the proxy reconstructions in deep tropics (5°N - 10°N) and in the Sahel region (15°N - 20°N). Our results point to the importance of desert-dust aerosol for simulating global and regional climates. [ABSTRACT FROM AUTHOR]

The Horizon2020 research project "BINGO" has investigated the impact of climate change on multiple water related problems at 15 research sites in six European countries. More than 20 hydrological models have been applied, driven with climatic decadal predictions from 2015 to 2024. The model applications focus on different water compartments and scales, such as flooding by combined sewer overflows in Badalona (Spain) and Bergen (Norway), changes in groundwater recharge for drinking water abstraction in the Veluwe, (the Netherlands), altered reservoir management in the Wupper river basin (Germany) and in Bergen (Norway), flooding in Cyprus, and increasing salinization in Portugal. Furthermore, consistent land- and water use scenarios have been developed in order to analyze and assess their impact on the water cycle. The model results show that the impacts of climate and socio-economic change vary between geographical regions and water compartments affected (i.e. groundwater or surface water). For example, at the Norwegian reservoir an increase of inflow is predicted, while the German reservoir is predicted to remain stable or even decrease. The groundwater levels at the Dutch and Portuguese site are both showing effects of not returning to the same antecedent conditions (reference period) or even featuring decreases. The combined sewer overflows at the Spanish and Norwegian sites both feature increasing trends. The comparison of the impacts of land-use and water use changes as well as extremal episodes also provide an indifferent picture. For example, land-use changes are predicted to further increase flood peaks in Cyprus, while no changes in the hydrographs of the German sites have been observed.The results are used by stakeholders, such as water providers and managers, local authorities, and others in order to be prepared for and to cope with near time climate change effects. Stakeholders have been included in Communities of Practice right from the project start and have influenced the modelling goals and protocols. Some of the models are implemented by stakeholders and are used operationally. Further, the model results have been used to conduct case sensitive risk analysis. The combined bottom-up (stakeholder, water managers, local problems) and top-down (modelling framework, decadal predictions, socio-economic scenarios) approach has shown to be a very promising way ahead to tackle multiple water problems at multiple sites and countries at the same time. [ABSTRACT FROM AUTHOR]

Alterations in global/regional climate conditions lead to changes in the hydrological cycle due to close inter-relations with the energy budget. In this perspective, evapotranspiration (ET) is the direct and most important link between the energy budget and the hydrological cycle since latent heat (energy flux) is equivalent to ET (water mass flux). Regarding the anthropogenic use and management of water resources, freshwater availability in rivers and lakes plays a crucial role for water supply, irrigation farming, and hydropower production for instance. In this perspective, hydro-systems with scarce water availability are particularly prone to climate change since water scarcity may be aggravated by decreased precipitation and/or increased ET.Here, we have analyzed the Lake Malawi Basin situated in semi-humid East Africa, sharing borders with Malawi, Tanzania, and Mozambique, regarding the susceptibility to climate change. Lake Malawi is the 9th largest lake on Earth (is in terms of water volume) and has only one outlet in the south, the Shire River which is intensively used for hydropower production. The installed electricity capacity and generation of hydropower accounts for 80.2 % and 98 %, respectively, of the Malawi's total electrical grid power generation.Analyzing data for the last five decades, it shows that annual inflow into the lake (~620 m³/s) is significantly compared to the annual outflow to the Shire River (~490 m³/s). This difference between in- and outflow is due to lake evaporation that exceeds average rainfall in the basin (~1,400 mm) by 20 to 30 %. In this perspective, water resources and electricity production are endangered by two phenomena: (1) Intra-annual variability of rainfall and ET may strongly affect discharge in the Shire River, which is only a small fraction of the basins´ overall water budget, meaning that small changes in rainfall or ET will lead to larger relative changes in Shire River discharge. Moreover, during drought years with low rainfall rates, lake evaporation will be on particular high levels, instead. (2) Global/regional warming will impact both the catchment- and lake water balances. Although trends in catchment rainfall over the last decades are not consistent and/or significant (yet), there is strong evidence that lake evaporation has already increased and will further increase in the future.Applying a catchment hydrology- and lake water balance model including sensitivity- and uncertainty analyses, we (i) show first results regarding changes in the water balance of Lake Malawi under recent and future climate change, and (ii) discuss the effects of these changes on streamflow in the Shire River and its consequences for water availability and (future) hydropower production. The results show that the water balance of the Lake Malawi Basin is particular sensitive to climate change, and similar conditions might occur in other semi-humid catchments in the tropics, too. [ABSTRACT FROM AUTHOR]

Extreme value (EV) analysis of remotely-sensed precipitation fields is a challenging problem due to the short record length of the datasets available, and the inevitable presence of measurement errors especially for intense rainfall rates. Despite their limitations, remote sensing estimates offer unique insight into the hydrological cycle at the global scale, and their space-time resolution makes available unprecedented information for hydrological applications. Here we develop and apply new statistical tools specifically designed to improve the estimation of extreme rainfall frequency based on short datasets from remote sensing sources. In particular we focus on precipitation estimates obtained by merging retrievals from multiple satellite-borne sensors, such as those in the Tropical Rainfall Measuring Mission (TRMM) and the Global Precipitation Measurement (GPM) mission. We describe a downscaling technique that can be used to connect key statistical properties of the rainfall fields obtained from satellite measurements at the daily aggregation time scale to those observed at the rain-gauge scale. The spatial correlation function, the intermittency structure, and the probability distribution function of rainfall intensities are downscaled from the satellite grid scale to the point scale, such that they can be meaningfully compared with the same quantities from observational records at single rain gauges at the ground. The donwscaled quantities are then used to define the Metastatistical Extreme Value distribution, and thus estimate average recurrence intervals of extreme events at the point scale. Here we present the application and testing of this combined methodology, and show that it can improve the estimation of extreme events in locations where long rainfall records at the ground are not available, which is the case for vast poorly gauged areas around the globe. [ABSTRACT FROM AUTHOR]

Launched on May-22, 2018, the GRACE Follow-On mission is set to continue the data record of mass transport in the Earth system that was initiated by the GRACE mission in 2002, and which ended in mid-2017 after more than 15 years of successful operations and science discoveries. GRACE provided a unique data record of monthly to decadal observations of global mass transport in the Earth system from observations of temporal variations in the Earth's gravity field. These observations have become indispensable for climate-related studies and provide critical measurements of Earth's time varying mass distribution. Tracking mass changes through gravity measurements provides unique observations of the evolution of the global water cycle, including ocean dynamics, polar ice mass changes, and global ground water changes.The GRACE Follow-On mission is the result of a partnership between NASA (US) and GFZ (Germany) to ensure continuity of this important climate record using a microwave ranging instrument, similar to the one used on GRACE. Additionally, GRACE Follow-On is demonstrating improved inter-satellite ranging from a Laser-Ranging Interferometer that promises to improve the spacecraft-to-spacecraft ranging measurements for the next-generation of mass change missions. In this presentation, we will provide status update of the post-launch, in-orbit checkout and early operations phases, and instrument and science payload performance and we will conclude with an outlook on mission lifetime. With the transition into the science operational phase in early 2019, we will discuss current plans and schedules for the first science data release. [ABSTRACT FROM AUTHOR]

Changes to the snowmelt regime are of critical importance to the hydrological cycle in many regions of the world. Recently Musselman et al (2017, Nature Climate Change) presented evidence to show that snowmelt rates are slower when temperatures are warmer in the western USA, while Wu et al's (2018, Geophysical Research Letters) study of the northern hemisphere suggested slower snowmelt rates for warmer temperatures in many places, but also faster snowmelt rates in regions with deeper snowpack. Musselman et al (2017) suggested that the reason for slower snowmelt might be that warming led to smaller snowpacks, which could be completely melted earlier in the warm season, on days when available energy was relatively low, and, crucially, not leaving any water to melt in late spring or summer, when incoming energy is higher. Wu et al (2018) suggested that the reason for faster snowmelt in deeper snowpacks (cf shallow snowpacks) might be the extra energy available for melt in late spring or early summer. At this stage the explanations for impact of warming on snowmelt rates remain ad hoc, without a unified explanation of the phenomena.Using a generalisation of Woods (2009, Advances in Water Resources), we present a simple theoretical explanation for the varying responses of melt rate to warming. The theory predicts that warming will lead to (i) faster snowmelt in very cold climates (ii) slower snowmelt in intermediate climates (iii) faster snowmelt in warm climates. The mechanisms are consistent with the explanations proposed by Musselman et al (2017) and Wu et al (2018). According to this theory, the dimensionless temperatures which define transitions from faster to slower and back to faster snowmelt are dependent on the precipitation regime: if the precipitation rate is higher, then the transition is predicted to occur at a higher (dimensionless) temperature.With this theory, it is possible to provide coherent first order explanations for the variety of snowmelt responses to warming, which may provide a useful organising principle for further data-based investigations into this issue, especially across large climate ranges. [ABSTRACT FROM AUTHOR]

Precipitation is an important component of the water cycle of High Asia and here particularlycrucial for the glacier mass balance and the seasonal dynamics of snow cover. To successfullymodel (i) past and future response of glaciers to climate forcing and (ii) the development ofsnow cover, reliable precipitation data are needed. However, this is especially difficult in highmountain areas where observational data, particularly at higher and complex terrain, arescarce. Beyond station data, other, spatial explicit data sources for precipitation are (i)simulated rainfall from models and (ii) retrievals from weather satellites. While precipitationpatterns are highly heterogeneous in both, time and space they are difficult to simulatecorrectly. With satellite data on the other hand, the assignment of rates of liquid andespecially solid precipitation is yet uncertain. To assess the differences among theseveral precipitation data sets, we compare selected accessible gridded data setsin High Mountain Asia. We present a comparison of five precipitation products(ERA-Interim, ERA5, HAR, JRA-55 and MERRA-2) and one satellite-based precipitationproduct (IMERG) for the period of April 1st to October 31st, 2014. The study area(80-87˚ E and 28-31˚ N) includes parts of India, a part of the Himalayas and partsof the Tibetan Plateau. The main statistical metrics used for comparison are thecorrelation coefficients r of different data sets and the corresponding coefficients ofdetermination r2 for different methods of temporal and spatial data aggregation. Wefurther compare the data sets to existing observational data available to the public. [ABSTRACT FROM AUTHOR]

Being the most important natural greenhouse gas and responsible for the largest known feedback mechanism for amplifying climate change, the role of water vapour is crucial in a warming climate. As a matter of fact, the amount and the time variability of atmospheric water vapour is globally governed by the temperature through the Clausius-Clapeyron equation which states that the water holding capacity increases at about 7% per degree Celsius increment in temperature. Of course, on local scales, water vapour also strongly influences atmospheric dynamics and the hydrologic cycle through latent heat transport and diabatic heating, and is, in particular, a source of clouds and precipitation. Atmospheric water vapour is highly variable, both in space and in time. Therefore, measuring it remains a demanding and challenging task. As a consequence, in this study, three different datasets have been taken into account. At 118 globally distributed Global Positioning System (GPS) sites, Integrated Water Vapour (IWV) is retrieved from a homogeneous data reprocessing from 1995-2010. At those site locations, also UV/VIS IWV satellite retrievals by GOME, SCIAMACHY and GOME-2, and ERA-Interim reanalysis output is used to study the time variability of the IWV. The IWV seasonal behaviour and the long-term variability are fitted together by means of a stepwise multiple linear regression of the station's time series, with a selection of regionally dependent candidate explanatory variables. Overall, the variables that are most frequently used and explain the largest fractions of the IWV variability are the surface temperature and precipitation. Also the surface pressure and tropopause pressure (in particular for higher latitude sites) are important contributors to the IWV time variability. All these variables also seem to account for the sign of long-term trend in the IWV time series to a large extent, when considered as explanatory variable. Furthermore, the multiple linear regression linked the IWV variability at some particular regions to teleconnection patterns or climate/oceanic indices like the North Oscillation index for West USA, the El Niňo Southern Oscillation (ENSO) for East Asia, the East Atlantic (associated with the North Atlantic Oscillation, NAO) index for Europe. [ABSTRACT FROM AUTHOR]

Hydrological-induced horizontal deformation have been already detected and precisely measured in the Eastern Southern Alps and Northern Dinarides from the analysis of GPS displacement time-series (Serpelloni et al., 2018). Since they appear to be temporally correlated with cumulated precipitation time-series, in this work we investigate how the hydrological cycle affect GPS time series in a portion of the Venetian Southern Alps, a region of particular tectonic interest since it is where large part of the Adria-Eurasia convergence is accommodated. Here the GPS network is denser than the surrounding regions; furthermore, we included new GPS stations and updated the time series in order to take into account the flood event that occurred in this area during October 2018. Ground-displacements time series from GPS stations have been analysed by applying a blind source separation algorithm based on variational Bayesian Independent Component Analysis. This analysis highlighted two annual common mode signals and a transient deformation signal. The latter is characterized by a spatially variable response in the horizontal components, causing a succession of horizontal extensions and contractions occurring about normal to natural fractures. We demonstrated that this transient signal is caused by the variation of the water storage in the hydrological basin of this area. Water storage has been modeled by using rainfall-runoff hydrological models, which describe how the precipitation over a basin turns into river flow once given as input rainfall, temperature and potential evapotranspiration. In order to understand how water storage variations generate the observed ground displacements, we built a 2D numerical model, accounting for the geological and topographical features of the study area. Then, we tested different sources of deformation in order to find the one that best reproduces the displacements obtained from the geodetic analysis. We found that the backthrust of the Bassano-Valdobbiadene fault, a major thrust of the south-verging seismogenic Venetian fold-and-thrust belt, is the preferred source of deformation. This backthrust fault is located north of a karstified mountain chain, corresponding to the anticline associated with the Bassano-Valdobbiadenet thrust fault. We made the hypothesis that the meteoric water penetrates through karst fractures at the top of the anticline and flows along the rock layers, converging to a sub-vertical fracture down to 1 km in correspondence of the backthrust of the main thrust fault. Here, the water accumulates because of the larger permeability of the fractured fault rocks, varying its level up to tens of meter and then generating pressure changes that cause the observed ground displacements. The largest pressure changes, associated with periods of larger displacements, cause significant increase/decrease of the Coulomb stress values down to 3 km, at seismogenic depths of the Bassano-Valdobbiadene thrust fault.Reference:Serpelloni, E., Pintori, F., Gualandi, A.,Scoccimarro, E., Cavaliere, A., Anderlini, L., et al. (2018). Hydrologically induced karst deformation: Insights from GPS measurements in the Adria-Eurasia plate boundary zone. Journal of Geophysical Research: Solid Earth, 123. https://doi.org/10.1002/2017JB015252 [ABSTRACT FROM AUTHOR]

The identification of hydration and dehydration reactions in natural rocks is crucial for thequantification of the deep water cycle. We have targeted one of the simplest possible systemsto investigate dehydration reactions – the contact metamorphic overprint of greenschistfacies serpentinites in the Eastern part of the Bergell intrusion (Northern Italy).Antigorite reacts to olivine + talc + chlorite at a distance of about 300-750 m from thecontact, producing nicely equilibrated and well preserved rocks. At 300 m from thecontact, the assemblage olivine + anthophyllite + chlorite + tremolite occurs (expectedtemperature range of 650-700 ˚ C). Surprisingly, anthophyllite is mainly present aselongated pseudomorphs in the olivine dominated matrix and all rocks display a strongretrograde overprint with late talc. Previous studies attributed this assemblage to peakmetamorphic conditions. However, 70 m from the contact orthopyroxene has been newlydiscovered. The inclusions of anthophyllite and olivine indicate orthopyroxene formationthrough the reaction olivine + anthophyllite = orthopyroxene + water occurring at∼700 ˚ C. Additionally, orthopyroxene contains inclusions of chlorite, Al-spineland hornblende indicating partial chlorite breakdown. Also these rocks displayextensive rehydration with the replacement of orthopyroxene by talc, explaining whyprevious studies have overlooked the orthopyroxene-in reaction. At 40 m from thecontact, the absence of chlorite inclusions in orthopyroxene, Al-spinel occurrence inthe matrix and Al-rich orthopyroxene inclusions in olivine indicate full chloritebreakdown according to the reaction chlorite = olivine + spinel + orthopyroxene +water. The most Al-rich orthopyroxene was only found as inclusions in olivine.The assemblage olivine + spinel + orthopyroxene + hornblende indicates that peakmetamorphic conditions reached ∼730 ˚ C during contact metamorphism, 160 ˚ Chigher than previously reported. Also the peak metamorphic assemblage is heavilyretrogressed. Former Al-spinel is replaced by magnetite-rich cores rimmed by chlorite, animportant marker in the field for the peak assemblage. Orthopyroxene is replaced byanthophyllite confining rehydration between 650-700 ˚ C in the vicinity of thecontact. The detailed microstructural investigation combined with experimental data andthermodynamic calculations allow the reconstruction of an invariant point at about 3kbar, 700 ˚ C where two of the most important low pressure dehydration reactions(anthophyllite- and chlorite-out) in ultramafic rocks cross each other, providing an importantpressure marker. Moreover, our study provides evidence for extensive high temperaturehydration immediately following peak dehydration. This feature is explained by fluidmovement from the antigorite breakdown reaction (that occurs in the outer contactaureole, where dehydration postdates peak metamorphism) towards the intrusion,essentially representing a self-rehydration and retrogression of the peak assemblage. [ABSTRACT FROM AUTHOR]

GRACE has been used widely for various hydrological applications. However, the GRACE product provides the observations of the global total water storage change with coarse spatial resolution. The insufficient spatial resolution limits its application to global and large-scale studies only. Improving the spatial resolution is vital for closing the terrestrial water cycle at small scales, monitoring droughts and floods, and assessing the regional water resources. In this study, a statistical assimilation algorithm is developed for spatial downscaling of GRACE, based on a combination of moving average and partial least-squares regression. By assimilating GRACE with WGHM and multiple hydrological variables (i.e. precipitation, evapotranspiration and runoff) from highly-resolved hydrological models, a finer spatial resolution of terrestrial water storage in the Amazon basin is achieved. For a validation, the downscaled water storage is compared with GRACE and WGHM as well as GLDAS by aggregation of grids over catchment, and through the misclosure of the water balance. In addition, the spatial and temporal patterns of separated modes of the assimilation results are analyzed as well as the patterns of linear trends and annual amplitudes. As a result, the downscaled terrestrial water storage retains the dominant signals from GRACE and benefits from WGHM in local details. Our assimilation results maintain the same accuracy level of GRACE and meanwhile enhance the variation along the main river stem in the basin. [ABSTRACT FROM AUTHOR]

Large-scale ocean evaporation is a key mechanism linking the energy and water budgets of oceans and the atmosphere. Because of its efficiency in transferring energy between these two components of the climate system, ocean evaporation plays a fundamental role for the diabatic forcing of the atmosphere. In addition, it is a major contributor to severe weather, for example, by favourably preconditioning the atmosphere for rapid cyclone intensification as well as downstream of the evaporation region in the form of heavy precipitation associated with the subsequent coherent transport of the evaporate.Studying atmospheric moisture uptake resulting from strong large-scale ocean evaporation (SLOE) on synoptic spatiotemporal scales thus provides important information about the dynamics of the atmospheric water cycle. Here, we present a methodology for an object-based climatological analysis of SLOE. In particular, we focus on transient events with a notable impact on the near-surface atmospheric moisture budget and its isotopic composition. These short-lived intense evaporation events explain nearly a quarter of global annual mean ocean evaporation, even though they occur only 6% of the time in the global average. The presented methodology provides the basis for a general Eulerian moisture source characterization using reanalysis data and can be easily applied to large datasets such as long-term climate simulations to effectively identify hot spots of strong moisture uptake by the atmosphere. In this presentation, we show three application examples of the SLOE identification scheme. First, the key role of the position of the storm track in shaping the spatial distribution of the occurrence of evaporation hotspots is discussed. Second, we show that during these events, the second order isotope parameter deuterium excess (d) of the marine boundary layer vapour is essentially determined by the evaporation flux signature. And third, a robust process‐based dynamical link is established between the variability of d in precipitation and the occurrence of SLOE at the moisture source. Potential implications of our findings for the interpretation of d as a proxy for the location and intensity of storm tracks are discussed.Overall, our results highlight the importance of transient weather systems in shaping the variability of the atmospheric water cycle at the synoptic to interannual timescales. Furthermore, they contribute towards a better understanding of the link between the dynamical drivers of this variability and stable water isotopes. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase precipitation in northern latitudes. Indeed, global observational data sets show statistically significant trends in precipitation averaged over land between 30°N and 60°N for the period 1901-2008. These changes would cause reduced salinity in the Baltic Sea, a semi-enclosed marginal sea with a large catchment area located in northern Europe. With the help of ocean simulations forced by historical atmospheric and hydrological reconstructions and local observations, we analyze the variability of sea surface salinity (SSS) of the Baltic Sea during 1850-2008. In line with other variables of the Baltic Sea water cycle, also the time series in SSS show low-frequency oscillations with a period of about 30 years. Hence, trends in absolute SSS are not significant on centennial scales. However, we found a statistically significant positive trend in the North-South gradient during 1900-2008 enhancing the sharp horizontal salinity gradient. With the help of sensitivity simulations, this change is attributed to local changes in the river runoff; the total annual river runoff to the Baltic Sea did not change. A detailed analysis of the individual rivers reveal increasing freshwater supply from the northernmost catchment indicating a footprint of the anthropogenic impact on salinity with consequences for the marine ecosystem and species distributions. [ABSTRACT FROM AUTHOR]

The δ18Oatm (i.e. δ18O of atmospheric O2) combines past variations of the low latitude water cycle and of the biosphere productivity. Over the last 800 ka, the δ18Oatm measured in EPICA Dome C (EDC) ice core shows orbital and millennial variations which are similar to the low latitude hydrological cycle variations observed in the δ18Ocalcite of the East Asian speleothems. The δ18Oatm is also a precious tool for ice core dating and chronology construction. However, the uncertainty associated with the use of this proxy as chronological constraint is high (6 ka) because of the lack of quantitative interpretation of the δ18Oatm including past evolution of oxygen fluxes and associated isotopic fractionation.This study presents a modelling approach for a quantitative interpretation of the δ18Oatm through the estimation of the oxygen fluxes and fractionation factors over several glacial-interglacial cycles. This approach combines (1) the coupling between the intermediate complexity climate model iLOVECLIM and the vegetation model CARAIB, (2) an estimation of the oxygen fluxes associated with photosynthesis and respiration processes, (3) an estimation of the isotopic composition of the oxygen in leaf water (δ18Oleaf) and (4) an estimation of the oxygen fractionation during oxygen uptake. This method associates the climatic parameters and water isotopes simulated by iLOVECLIM with the changes in vegetation distribution and terrestrial biosphere productivity obtained by CARAIB for 26 PFTs (Plant Functional Types) instead of the 2 PFTs previously used in iLOVECLIM. We present here the results of this new coupled model over several glacial-interglacial cycles and discuss the spatial distribution of the vegetation and δ18Oleaf, as well as the carbon and oxygen fluxes linked to the continental biosphere productivity. A focus on the Last Glacial Maximum can also allow a direct comparison with previous "offline" simulations with General Circulation Models. The δ18Oleaf corresponding to the terrestrial contribution of the δ18Oatm, our results can be compared, as a first approximation, to the isotopic δ18Oatm data measured in EDC ice core. [ABSTRACT FROM AUTHOR]

In this study we investigate the effect of different downscaling methods on the hydrologic cycle of a Mediterranean catchment in Sardinia (Italy) that is prone to extreme flooding. To this aim, we use an ensemble of four combinations of GCM - RCM projections (see Deidda et al., 2013, and Langousis et al., 2016), statistically downscaled using: a) the parametric statistical scheme of Mamalakis et al. (2017), and b) its widely used non-parametric variant based on empirically derived Q-Q (quantile-quantile) correction relationships. In particular, we analyze differences in the climate projections of the available downscaled climate model outputs, considering or not the elevation factor (in the latter case by re-projecting outputs at the mean elevation of the basin). We further quantify the impact of these differences on modeled hydrologic variables. The hydrologic impact of climate change is evaluated during five 30-year periods (1951-1980, 1981-2010, 2011-2040, 2041-2070, 2071-2100), focusing on a set of variables that characterize the water balance, including precipitation, air temperature, discharge, leakage, and actual evapotranspiration. The response of the basin is quantified at the outlet and also at 33 subcatchments, analyzing the influence of features such as the area and mean elevation of the subcatchments. The results show that the choice of climate model and downscaling method leads to variations in the simulated hydrologic response of the basin, and that this effect varies also by subwatershed. Notwithstanding these differences, the reduction in precipitation predicted by the climate models is more pronounced as the watershed area increases, and as the altitude decreases. References:Deidda, R., M. Marrocu, G. Caroletti, G. Pusceddu, A. Langousis, V. Lucarini, M. Puliga, and A. Speranza (2013). Regional climate models' performance in representing precipitation and temperature over selected Mediterranean areas, Hydrol. Earth Syst. Sci., 17(12), 5041-5059, doi:10.5194/hess-17-5041-2013.Langousis, A., A. Mamalakis, R. Deidda and M. Marrocu (2016). Assessing the relative effectiveness of statistical downscaling and distribution mapping in reproducing rainfall statistics based on climate model results, Water Resour. Res., 52, doi:10.1002/2015WR017556.Mamalakis, A., A. Langousis, R. Deidda, and M. Marrocu (2017). A parametric approach for simultaneous bias correction and high-resolution downscaling of climate model rainfall, Water Resour. Res., 53, doi:10.1002/2016WR019578. [ABSTRACT FROM AUTHOR]