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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]

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]

Under the framework of the EU-Horizon 2020 project BINGO (Bringing INnovation to onGOing water management), climate change impacts on the water cycle in the Wupper catchment area are being studied. For this purpose, the Soil and Water Assessment Tool (SWAT) has been set up, calibrated and validated. The model integrates detailed spatially and temporarily distributed soil, land-surface and meteorological information and can therefore closely link the impact of changes in climate variables to future changes in the numerous hydrological system variables. In this study, short-term (decadal) as well as long-term (centennial) impacts of climate change scenarios are examined, for the Wupper sub-catchment "Große Dhünn". This sub-catchment generates the inflow to a large reservoir, which is used as drinking water source for about 0.5 million people and as flood protection system for downstream areas. Changes of principal water balance components due to climate change, are therefore of high importance in this region.Climate change information are derived from medium-term decadal predictions, based on the MiKlip framework, for the time span 2015-2024, as well as from long-term IPCC-RCP scenarios, for the years 2006-2100. The study assesses potential future hydrological changes in the "Große Dhünn" catchment, based on both data sets and compares the projected changes for the overlapping time period (2015-2024).Decadal predictions as well as IPCC-RCP scenarios indicate that in the near future, winter months will experience reduced reservoir inflow, while summer inflow will slightly increase. The main reason for the decreasing winter discharge rates lays in decreasing precipitation during the respective winter months. In addition, temperature and concurrently also ET rates will increase during winter, which will intensify the decrease in discharge rates. Increasing summer temperatures and ET rates are compensated by increasing summer precipitation rates, and are resulting in a slight increase in summer discharge rates.For long-term predictions however, RCP scenarios indicate that under both RCP scenarios a significant reduction of inflow to the reservoir is expected in all seasons. Furthermore low flows will shift from early to late summer, making a careful management and saving of water resources until later in the hydrological year necessary.A comparison of simulated runoff based on decadal predictions and IPCC-RCP runoff scenarios reveals the interesting fact, that decadal predictions might underestimate the variability of future runoff responses to climate change. While RCP scenarios show a similar variability in runoff compared to historical data, decadal predictions indicate a significant reduction in future runoff variability. This is especially important to consider for future reservoir management, considering the range of potential extreme high and low flows in the near-future. [ABSTRACT FROM AUTHOR]