Precipitation trends in Spanish hydrological divisions, 1946-2005

This paper presents an analysis of precipitation changes in the main Hydrological Divisions (HDs; 'Cuencas Hidrograficas', Water Planning Divisions) in Spain from 1946-2005. Trend analysis revealed several monthly long-term variations and important spatial differences that should be taken into account for any national water-planning scheme. The most spatially coherent signals were a negative trend observed in March and June, affecting all catchments (HDs), and a positive trend in October, which was particularly evident in the northwestern catchments. These caused a redistribution of precipitation throughout the year, with a reduction in the length of the wet season (due to the negative trend in March) and a concentration of precipitation at the beginning of the wet season in October. A running trend analysis revealed variability in the long-term tendency which, although quite persistent, changed in strength between sub-periods.