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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]

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]

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]

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]

As a typical alpine marsh wetland on the Qinghai-Tibet Plateau, the Zoige Wetland plays an important role in the water source recharge of Yellow River. Meanwhile, it is more sensitive to climate change. Therefore, it is necessary to study the hydrological cycle of Zoige Wetland and the impact of climate change, which will also provide important support and reference for the study of hydrological process, and protection of wetland water resources in Alpine areas. Based on the distributed hydrological model, this paper analyzed the runoff process in the Zoige wetland basin, and explored the trend of runoff variation in the Zoige wetland basin under different climate change scenarios in the next 30 years from 2020 to 2050. The impact of climate change on wetland runoff were also discussed. Results showed that the runoff in the Zoige Wetland basin decreased under the future climate change scenario. The rate of runoff reduction was the largest in Machu station, followed by Zoige station, and finally Tangke station. The reduction in non-flooding runoff is significantly higher than that in the flood season. The runoff during non-flood season in the Zoige Wetland basin from 2020 to 2050 will decrease by more than 25% in the future climate change scenario. The sharp decline in non-flooded runoff may have an impact on the protection of the Zoige Wetland and the management of water resources in the middle reaches of the Yellow River and downstream areas. This poses more stringent requirements for the protection of the Zoige Wetland in response to future climate change. Under future climate change scenarios, how to strengthen the management and protection of wetland water resources and prevent the degradation and atrophy of wetlands is the issue we need to further discuss and consider. [ABSTRACT FROM AUTHOR]