Modeling the impacts of future climate changeon water resources for the Gallego river basin (Spain)

Global changes in climate may have large impacts on regional water resources and the frequency of drought or flood events. Changes in precipitation or temperature may also severely modify the available water resources for users in several sectors. Here, we examine climate change scenarios for the Gallego river (a tributary of the larger Ebro river in Spain) in the context of quantitative water resources management for the basin. Projected changes to precipitation and temperature are derived from an ensemble of 6 Regional Climate Models (RCMs) run for the period 2071–2100 under the SRES A2 emissions scenario and are subsequently bias corrected before input into a hydrological model. The use of RCM ensembles is important for the incorporation of uncertainties derived from different model structures, parameterizations and boundary conditions into the hydrological modeling process and subsequent climate change impact assessment. All 6 RCMs project decreases in annual precipitation with some RCMs projecting a slight increase between December and February. Additionally, all models project a >3C increase in annual mean temperature over the basin, with some models projecting a 9C temperature increase during summer months. Hydrological simulations using the GEOTRANSF model, with the climate change scenarios as input, show that projected water availability for the Gallego is lower for the 2071–2100 period than for 1961–1990, with an increasing number of dry years. During the water-storage period (October to March), medium to low flows are reduced, while during the irrigation period (April to September), streamflow is reduced across the entire range of flows. The projected changes vary across the basin and are also not uniform throughout the year. Stronger drying occurs during the summer with potentially important implications for water resource management across many sectors including agriculture, with a reduction in the amount of water available for irrigation and hydropower generation, due to projected seasonal reductions in reservoir levels.