Climate-driven trends in the streamflow records of a reference hydrologic network in Southern Spain

Monthly streamflow records from a set of gauging stations, selected to form a reference hydrologic network, are analyzed together with precipitation and temperature data to establish whether the streamflows in the Guadalquivir River Basin have experienced changes during the last half of the 20th century that can be attributed to hydrological forcing. The observed seasonal and annual streamflows in the reference network have undergone generalized and significant decreases during the study period. Annual rainfall did not experienced statistically significant changes. The observed trends in streamflows may be attributed to either land-use changes, or to the statistically significant changes exhibited both by yearly potential evapotranspiration values and by the seasonal redistribution of precipitation. In the attribution work conducted using both data-based and simulation-based methods, the intra-annual redistribution of precipitation is shown to be the main statistically significant climate-driver of streamflow change. The contributions of other non-climate factors, such as changes in land cover, to the reduction in annual streamflows are shown to be minor in comparison.