Effects of warming processes on droughts and water resources in the NW Iberian Peninsula (1930−2006)

We analysed the evolution of drought on the NW Iberian Peninsula from 1930 to 2006, and identified differences between the effects of precipitation variability and warming processes on drought severity and surface water resources. Two drought indices were used, one based on precipitation (the standardised precipitation index, SPI) and the other based on water balance, as reflected by the difference between precipitation and potential evapotranspiration, PET (the standardised precipitation evapotranspiration index, SPEI). The results show that precipitation has increased in the region, but a significant increase has also occurred in PET. No statistically significant differences were found over the study period for the severity of drought, as assessed by both the SPI and SPEI. In addition, although in the last 3 decades the mean duration of drought episodes has increased by approximately 1 mo as a consequence of the increase of the PET rates, the differences are not statistically significant. River discharge is mainly driven by precipitation variability, whereas warming processes did not have a noticeable influence on the streamflow variability between 1930 and 2006. The implications of global warming projected by global climate models on future drought severity and the availability of water resources are highly relevant in the near future.