Search

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]

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]

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 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]

The transboundary river basin Ganges-Brahmaputra (GB) of over 1.7 million km2 in size is home of estimated over 600 million inhabitants, distributed between India, China, Nepal, Bangladesh and Bhutan. Understanding hydrological dynamics in this region is of immense importance for water management and supply. Global-scale hydrological models like the WaterGAP Global Hydrological Model (WGHM) provide a means of analyzing hydrological processes and the water cycle dynamics in such a complex river basin towards water availability assessment at a regional scale. However, huge uncertainty of large-scale hydrological models hinders their reliable application. A Pareto-based optimization concept for more than one calibration variable can be used to reduce the model uncertainty and equifinality through model calibration prior to any model application. Here, we calibrated the 12 and 11 most sensitive parameters of WGHM for the Ganges and Brahmaputra, respectively. The sensitive parameters were identified using Morris's Elementary Effect Test (EET) method for each basin. The model was calibrated against four observations – in situ river discharge (Q), satellite-derived evapotranspiration (ET), surface water storage variations (SWSV) from multi-satellite observations and GRACE-based total storage variations (TWSV). As calibration objective for each observable the Kling-Gupta Efficiency of basin-scale monthly averages was used. The Pareto frontier of the objectives was approximated using the Multi-Objective Evolutionary Algorithm Borg-MOEA. Borg-MOEA performed well in estimating Pareto optimal model parameters as well as identifying the trade-offs among objectives. Good model performance for the calibrated variables usually was at the expense of simulation performance for the other variables that were not included in calibration. The largest trade-off was observed between river discharge (Q) and surface water storage variations (SWSV) which suggests that constraining the model only with discharge observations results in inappropriate simulations of SWSV. We observed poor performance of WGHM to generate accurate SWS in fast responding basin like Ganges especially during heavy rainfall in monsoon. In general, however, any additional observation considered during calibration helped to better represent the hydrological dynamics, with good performance for all considered performance criteria. [ABSTRACT FROM AUTHOR]

Hydrated ultramafic rocks play a key role in the transport of water from the surface to the mantle along subduction zones. Many key geochemical and geophysical features of Earth depend on this deep water cycle. Previous studies have demonstrated that antigorite and chlorite are the dominant water carriers in subducted slabs up to pressures corresponding to 100-150 km depth. Beyond 200 km depth hydrous Mg-silicates ("alphabet phases" A, E, D) as well as wadsleyite and ringwoodite potentially can host weight per cent of H2O. The phase relations of hydrous ultramafic rocks and the geotherms in the critical depth range of 120-200 km will determine how much water is cycled through arc magmatism back to the Earth surface and how much water is subducted to the deeper mantle. To date, very limited information is available to constrain this crucial aspect of the deep water cycle. We have conducted piston cylinder experiments in the range of 4-6.2 GPa and 600-850°C to address subduction water recycling in chlorite-rich ultramafic rocks using natural starting materials. Chlorite is stable up to 800°C at 4 GPa and then there is a moderate backbend of chlorite stability to 5.6 GPa, 740°C. Above 5.6 GPa, chlorite reacts to a hydrous Mg-Al-silicate, the 11.5 Å phase (12 wt% H2O) + garnet + olivine. Above 6.2 GPa, 600-700°C chlorite breaks down to Mg-sursassite (7.2 wt% H2O) + 11.5 Å phase + olivine. The transition of chlorite to these other hydrous Mg-Al-silicates occurs at significantly higher temperature and lower pressure conditions than previously reported, with important consequences for the deep water cycle.The new results show that along warm and intermediate slab geotherms, all hydrous phases in subducted ultramafic rocks will break down. Also in the warmer mantle wedge, no hydrous phases are stable. Thus, for these conditions, a few 100 ppm of water will be stored solely in the nominally anhydrous minerals garnet, pyroxenes and olivine. However in cold subduction zones and even more so in the cold interior of subducted slabs, water can be transferred from the hydrous phase chlorite via the hydrous 11.5 Å phase and Mg-sursassite to the hydrous "alphabet phases", providing an efficient mechanism to transport significant amounts of water to the deeper mantle along subduction zones. Thus, water incorporated in hydrous ultramafic rocks in the uppermost part of the subducted slab and in the hydrated forearc will not be able to be transported beyond 150 km depth and will be mostly recycled through arc magamatism at timescales of a few million years. In contrast, water incorporated in the slab lithospheric mantle due to hydration at bending faults will likely be transported to the deeper mantle and might return to the surface only after residence times of several 100 million years. [ABSTRACT FROM AUTHOR]

In order to evaluate influences of climate changes on ecosystems in the polar regions, it isnecessary to understand the hydrological cycle in those regions. While interactions betweengroundwater and surface water have been recognized as an important component of thehydrological cycle, studies have been rare with regard to this aspect in the polar regions,particularly for groundwater. This study investigated hydrogeological characteristics ofgroundwater and surface water in the region near King Sejong Station, King George Island,Antarctica. Forty seven groundwater, surface water, and snow samples were collected inJanuary 2018, and major anions, cations, trace elements, and oxygen and hydrogen isotopeswere analyzed. Also, groundwater influx and outflux to/from two small ponds were measuredusing seepage meters. The results of water analysis indicated that groundwater chemistry isdistinguishable with those of surface water and snow by higher concentrations ofcalcium, magnesium, silicone, and bicarbonate. The composition of snow appeared tobe affected by sea spray. The isotopic compositions of hydrogen and oxygen forsnow followed the Global Meteoric Water Line; however, those of groundwater andsurface water slightly deviated from the line, indicating that there might be isotopicfractionation due to sublimation and melting of snow after precipitation. The measuredgroundwater influx to surface water was relatively consistent between 2.2×10−9 m/sand 3.0×10−9 m/s in one pond, while in another pond, both influx (2.0×10−10m/s∼2.7×10−9 m/s; from groundwater to surface water) and outflux (-9.9×10−10m/s∼-7.3×10−9 m/s; from surface water to groundwater) were measured, indicating thatgroundwater-surface water interaction can be very dynamic in the study site. This studypresents groundwater chemistry and groundwater-surface water flux data in an area ofAntarctica, which have not been reported in previous studies; thus, it can provide a basis forevaluating hydrogeological characteristics of and impacts of climate changes onactive layers and permafrost in Antarctica. This research was supported by the PolarAcademic Program (PE18900) of the Korea Polar Research Institute and by theBasic Science Research Program through the National Research Foundation ofKorea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1A02937479). [ABSTRACT FROM AUTHOR]

Rainfall production is a fundamental process within the Earth's hydrological cycle because it represents both a principal forcing term in surface water budgets, and its energetics corollary, latent heating, is the principal source of atmospheric diabatic heating. Latent heat release itself is a consequence of phase changes between the vapor, liquid, and frozen states of water. The properties of the vertical distribution of latent heat release modulate large-scale meridional and zonal circulations within the Tropics - as well as modify the energetic efficiencies of mid-latitude weather systems. This paper highlights the retrieval of latent heat release from satellite measurements generated by the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Mission (GPM) satellite observatory, which were launched in November 1997 and February 2014, respectively. Both TRMM and GPM measurements have been providing an accurate four-dimensional account of rainfall over the global Tropics and mid-latitudes: information that can be used to estimate the space-time structure of latent heating.Two sets of latent heating retrieval algorithm methodologies (Goddard Convective-Stratiform or CSH, and Japan Spectral Latent Heating or SLH) have been developed to estimate latent heating based on rain rate profile retrievals obtained from TRMM and GPM measurements. The differences and similarities between the CSH and SLH algorithm design will be presented. The presentation then will provide the results of LH structures derived from the TRMM and GPM. At the end of presentation, the further research on latent heating retrieval from satellites will be discussed. [ABSTRACT FROM AUTHOR]

Since 2002, the GRACE mission (Gravity Recovery and Climate Experiment) – a joint mission by NASA and DLR – has observed the terrestrial water storage and has improved our knowledge of the global water cycle significantly over the last 16 years. GRACE-derived information has been used to improve hydrological models in terms of model calibration and data assimilation. However, localized small-scale mass variations, such as caused by human-controlled reservoirs, that are spatially below the GRACE resolution but large enough in magnitude, can have a strong influence on the mass change signal. Even though GRACE can "see" these mass changes, they do not necessarily appear exactly at the location of their origin and with the correct magnitude. Thus they can distort the water storage estimate for neighboring areas or the average over a river basin. In the newly established DFG Research Unit GlobalCDA, GRACE data (among various other geodetic and remote sensing data sets) shall be used to improve a global hydrological model via calibration and data assimilation. Prior to data assimilation, however, the GRACE signal has to be cleaned from these localized features (e.g. reservoir effects), which are not properly represented in the model, in order to make GRACE water storage estimates consistent with the model output.In this presentation, we will discuss methods to quantify and remove the effect of the concentrated mass signals from the GRACE data based on a forward modeling of the expected small-scale mass features using altimetry and remote sensing information. Furthermore, we will discuss possibilities to include a comprehensive dataset of several types of surface water bodies (e.g. natural lakes, rivers) to estimate their combined influence on the GRACE signal on a basin-wide scale. [ABSTRACT FROM AUTHOR]

Actual evapotranspiration (ETА) is a fundamental variable of the hydrological cycle playing a principal role on surface water balance. Detailed ETА estimation data is important subject for numerous applications including irrigation management, water resources planning and environmental studies. At the plot scale ETА can be accurately determined from detailed ground observations but at regional (even field) scale, numerous time-consuming and expensive installations would be required. In the last few decades, earth observation technology become provide spatially distributed cost-effective information for ETА maps production at regional scale. The increased availability of observed data for long monitoring periods and of advanced techniques for the spatiotemporal analysis of acquired information allows to describe trends in evapotranspiration behavior and find the reason of it. In this study the MODerate Resolution Imaging Spectroradiometer (MODIS) ETА product data (8 days temporal resolution for the period of 2000-2017) were integrated and processed in GIS environment in order to obtain the final goal of finding spatiotemporal distribution of the ETА for the territory of two study sites with high agricultural activities. Methodology used to assess spatial distribution of ETА trend over study regions for warm year periods (spring, summer and autumn) is consisted on: (1) building gridded time series datasets; (2) time series testing for stationary; (3) trend calculation by modified Mann-Kendall test for non-stationary time series; (4) analyzing of spatial patterns distribution. Obtained results show evidence of strong correlation in ETА behavior and agriculture farming changes (crop water demand). This means that losses due to evapotranspiration in agriculture can be handled in a way allowing to assure the best conditions for agricultural needs of the region.Authors express their gratitude to the Russian Foundation for Basic Research for providing financial support of the project 16-05-01097. [ABSTRACT FROM AUTHOR]

When characterising regional or global climate, due to its implications for both local impacts and the environmental water cycle, rainfall is one of the most important atmospheric variables to be considered. For this reason, annual and seasonal trends of hourly to daily rainfall extremes have been an important object of climatological studies in the past. In the context of the project INTEXseas (An integrated weather-system perspective on the characteristics, dynamics and impacts of extreme seasons), funded by the European research council (ERC), extreme rainy seasons are introduced as a new concept in climate research.In this study, an extreme rainy season is defined as an anomalously 90-days wet period experienced by a region. Using daily rainfall fields of multi-year global gridded datasets from reanalyses and climate simulations, we discuss the particularities of the identified extreme wet seasons in each region and we make a point on the relationship between the anomalously high seasonal averages and the number and nature of the extreme short-term weather events included in these averages. To gain an insight into the different aspects of extreme wet seasons in different regions of the world, our results are discussed also taking into consideration the amplitude of anomalies of the fields of the atmospheric water budget terms that contribute to rainfall, i.e., surface evaporation and the vertical integral of the horizontal moisture flux divergence. [ABSTRACT FROM AUTHOR]

Snow water equivalent (SWE) is a key property of the seasonal snow cover. The water stored in the snowpack is a crucial contribution to the hydrological cycle in mountain areas. Estimating the spatial distribution and temporal evolution of SWE in mountain region is currently considered as one of the most important unsolved problems in snow hydrology. Direct measurements of SWE are still essential but are scarce and mostly non-continuous (manual measurements) or rather expensive (automatic scales or snow pillows). Recently, a novel in-situ measurement technique based on freely-available L-band Global Navigation Satellite Signals (GNSS) signals, like GPS signals, showed promising results in deriving SWE. This snow measurement technique is in general based on the combination of GNSS carrier phase measurements indicating signal time delay and GNSS signals strength information indicating signal attenuation within the snowpack. To derive the SWE, the signal time delay and attenuation are obtained from the signal differences between a GNSS antenna buried below the snowpack and a reference antenna above the snow cover. This method has been tested and validated at the high-alpine test site Weissfluhjoch (Eastern Swiss Alps, 2540 m asl.) and seems to work well for the snow conditions met at this elevation. However, the snow characteristics can vary considerably depending on location and elevation. At lower elevations the snow cover is normally shallower and is more frequently subject to melt-freeze cycles leading to faster snow aging and different snow densities. Moreover, it was not yet tested, if a rapid transition from dry to wet snow conditions is a challenge for deriving SWE by this GNSS method. To test these potential issues and aiming to improve our method, we installed four GNSS stations along a steep elevation gradient (820 m, 1185 m, 1510 m, and 2540 m asl.) within only a few kilometres in the Eastern Swiss Alps in autumn 2018. For validation purposes, the snow height is monitored continuously and automatically with additional sensors. SWE is measured at least biweekly at all locations. Moreover, at the two higher elevations, SWE is also measured continuously with snow scales. We present preliminary results from the ongoing season along this steep elevation gradient. The latest GNSS processing steps as well as our recent integration of Galileo besides GPS signals, which is particular useful to increase GNSS satellite visibility for valley sites, will be shown. Finally, we will assess whether the method is suitable for operational use at different elevations, in steep valley sites and under various snow conditions for deriving SWE continuously with reasonable costs. [ABSTRACT FROM AUTHOR]

Interannual variability of Antarctic Intermediate Water (AAIW) in the tropical North Atlantic is investigated using the GECCO\superscript{2} ocean state estimate and Argo data. AAIW salinity variability near the western boundary is shown to be highly correlated with the western boundary current (WBC) transport on interannual timescales. Northward propagating anomalies are associated with the WBC variability that, in turn, is related to the large-scale wind stress curl forcing by means of the Sverdrup balance. AAIW anomalies also propagate westward with the speed of baroclinic Rossby waves, indicating that the westward propagation of baroclinic Rossby waves also plays a role in the variability of AAIW characteristics. Slow eastward spreading of AAIW anomalies is also identified on decadal timescales. Understanding the observed interannual and decadal variability of AAIW salinity is important to properly interpret salinity changes with respect to changes in the hydrological cycle. [ABSTRACT FROM AUTHOR]