  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 XXth century that
can be attributed to hydrological forcing. The observed streamflows in the
reference network have undergone generalized and significant decreases both at
seasonal and annual scales during the study period. Annual rainfall, though,
did not experienced statistically significant changes. The observed trends in
streamflows can be attributed to either land-use changes, or to the
statistically significant changes exhibited both by yearly potential
evapotranspiration values and by the seasonal distribution 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 the change in land cover,
to the reduction in annual streamflows are shown to be minor in comparison.
