  This study explores the impacts of climate change on the hydrology of the
headwater areas of the Duero River Basin, the largest basin of the Iberian
Peninsula. To this end, an ensemble of 18 Euro-CORDEX model experiments was
gathered for 1975-2005 and 2021-2100, under the RCP4.5 and RCP8.5, and were
used as the meteorological forcings of the Variable Infiltration Capacity (VIC)
during the hydrological modelling exercise. The projected hydrologic changes
for the future period were analyzed at annual and seasonal scales using several
evaluation metrics, such as the delta changes of the atmospheric and land
variables, the runoff and evapotranspiration ratios of the overall water
balance, the snowmelt contribution to the total streamflow and the centroid
position for the daily hydrograph of the average hydrologic year. Annual
streamflow reductions of up to 40% were attained in various parts of the basin
for 2071-2100 under RCP8.5 scenario, and resulted from the precipitation
decreases in the southern subwatersheds and the combined effect of the
precipitation decreases and evapotranspiration increases in the north. The
runoff and the evapotranspiration ratios evinced a tendency towards an
evaporative regime in the north part of the basin and a strengthening of the
evaporative response in the south. Seasonal streamflow changes were mostly
negative and dependent on the season considered, with greater detriments in
spring and summer, and less intense ones in autumn and winter. The snowmelt
contribution to the total streamflow was strongly diminished with decreases
reaching -80% in autumn and spring, thus pointing to a change in the snow
regime for the Duero mountains. Finally, the annual and seasonal changes of the
centroid position accounted for the shape changes of the hydrograph,
constituting a measure of seasonality and reflecting high correlations degrees
with the streamflow delta changes.
