Groundwater discharge in high-mountain watersheds: A valuable resource for downstream semi-arid zones. The case of the Bérchules River in Sierra Nevada (Southern Spain).

Aquifers in permeable formations developed in high-mountain watersheds slow down the transfer of snowmelt to rivers, modifying rivers' flow pattern. To gain insight into the processes that control the hydrologic response of such systems the role played by groundwater in an alpine basin located at the southeastern part of the Iberian Peninsula is investigated. As data in these environments is generally scarce and its variability is high, simple lumped parameter hydrological models that consider the groundwater component and snow accumulation and melting are needed. Instead of using existing models that use many parameters, the Témez lumped hydrological model of common use in Spain and Ibero-American countries is selected and modified to consider snow to get a simplified tool to separate hydrograph components. The result is the TDD model (Témez-Degree Day) which is applied in a high mountain watershed with seasonal snow cover in Southern Spain to help in quantifying groundwater recharge and determining the groundwater contribution to the outflow. Average groundwater recharge is about 23% of the precipitation, and groundwater contribution to total outflow ranges between 70 and 97%. Direct surface runoff is 1% of precipitation. These values depend on the existence of snow. Results are consistent with those obtained with chloride atmospheric deposition mass balances by other authors. They highlight the important role of groundwater in high mountain areas, which is enhanced by seasonal snow cover. Results compare well with other areas. This effect is often neglected in water planning, but can be easily taken into account just by extending the water balance tool in use, or any other, following the procedure that has being developed.