Projections of groundwater recharge changes in the Mediterranean: Uncertainties of simulating groundwater recharge in global hydrological models

In the Mediterranean, climate change effects are projected to be particularly strong, and with them, the already prominent use of groundwater as a source for drinking water and irrigation is likely to increase. The sustainable amount of water that can be extracted from an aquifer is determined by groundwater recharge. Although important as an indicator for groundwater availability, quantification of this process is not sufficiently accurate at large scales due to feedbacks of processes and mechanisms. It is difficult to measure, and its rainfall based simulation is challenging because the absolute uncertainties of other water balance components accumulate, especially in dry areas.

Global hydrological models (GHMs) have proven to be a valuable tool to assess the impacts of climate change on the global water cycle; however, their simulation of groundwater recharge remains uncertain. In this presentation, we show results of an investigation of groundwater recharge by using an ensemble of eight GHMs and four global circulation models (GCMs). The assessment focuses on the Mediterranean for two evaluation periods 1861-2006 and 2006-2100. Of particular interest are the seasonal patterns of groundwater recharge and whether the models show similar seasonal patterns in the past and under different climate change scenarios. The Mediterranean is versatile in terms of topography and climatic conditions. Thus, the variation of groundwater recharge in both spatial and temporal terms is examined thoroughly.

Further, precipitation characteristics can have significant impacts on recharge amounts. Therefore, the correlation of the GCMs daily precipitation data with the modelled recharge is analyzed. Results show a significant variation within the ensemble. Overall, a declining trend in groundwater recharge is dominant.