The Arlanza river at headwater : recent evolution and trends under climatic change conditions

Abstract

The headwater catchments in mountain areas are highly sensitive under conditions of global change and their fluvial regimes and hydrological resources are likely to be notably modified. The general predictions for the Mediterranean region are the increase in temperature and decrease in rainfall together with a higher frequency of extreme events, both droughts and floods. The Arlanza basin at the headwater was selected as a control sector to examine the recent evolution and trends in discharge. At the gauging station of Castrovido, a general decreasing trend of annual discharge was found for the 1960-2002 hydrological period. The main decrease period started in 1980 and discharge was reduced by almost 50%. Since 1995, extreme floods were relatively more frequent and also the largest range of variation in the maxima annual flood was found. Under climatic change conditions and in order to promote the rational planning of hydrological resources, a fundamental understanding of patterns and trends of discharge is required but specially in forest catchments as their headwaters are main sources of water to the lowlands.