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Catchment Management under Environmental Change: Impact of Land Cover Change on Water Resources

Abstract Since the second third of the 20th century, it has been clearly established in the hydrological science that an increase of the forest cover in a catchment determines a decrease in water resources from this catchment. Nevertheless, the application of this paradigm for catchment management has been delayed. In Spain, extensive mountain areas that were farmed or grazed in the past have been abandoned during the last 50 years and undergone spontaneous or induced afforestation, mainly by pine trees. The historical flow records of several Spanish rivers during the last 50 years show significant decreases that average an annual reduction of about 0.4 percent of mean annual flow, whereas in the Ebro River the annual decrease was as high as 0.63 percent of mean annual flow. About one-third of these decreases were not explained by increases in water consumption by irrigation or by climate variability, but should be attributed to an increase in evaporation from the headwaters. These results confirm that the assessment of future water resources must take into account the past and expected changes in land cover in the catchment headwaters and that land use and cover planning should be integrated in the management of catchment water resources, especially in scarce water environments.