Global Change and Water Resources in the Mediterranean Mountains: Threats and Opportunities

Abstract

The Department of Geoenvironmental Processes and Global Change (DGPGC) at the Pyrenean Institute of Ecology – CSIC (Spanish Council for Scientific Research) has been doing research on Environmental Hydrology at various spatial and temporal scales since 1990. Hydrological consequences of land cover change in mountain headwaters have proved to be complex and scale dependent. At plot scale, abandonment of traditional cultivation practices in the valley slopes had the consequence of decreasing runoff production and soil erosion and sediment yield, which were more pronounced as the revegetation process progressed. At catchment scale the differences are smaller, because part of the water that infiltrates into the soils in the vegetated areas reappears later in lower parts of the catchment. An important effect of revegetation at catchment scale is the attenuation of the catchment's response to any precipitation event (except the most extreme ones), resulting in less torrential behaviour. A decrease in total water yield has also been observed in the long term evolution (1945-1995) of discharge series in the Central Pyrenees basins, during a period in which no significant decrease of precipitation has been recorded. We attribute this trend to the process of revegetation after farmland abandonment. Changes have been found also on the monthly discharge regimen, as well as on the frequency of high flows, which decreased during the studied period. All this changes have increased the stress on water resources management, as shown by changes in reservoir management practices. We question whether we will be able to satisfy water demands in the near future, considering expected changes in climate and land cover, and we show the importance of increasing research effort on water resources in global change scenarios.