The future of Iberian droughts: a deeper analysis based on multi-scenario and a multi-model ensemble approach

As a result of warming and precipitation deficits, the increasing shortage of water resources, droughts have become one of the main drivers of desertification, land degradation and food insecurity with direct impacts on ecosystems and society, especially in fragile communities. Over the Iberian Peninsula, a known climate change hotspot, the occurrence of droughts varies in intensity and severity, being its assessment under present and future conditions an important tool for adaptation measures. Here, for the first time, we present a comprehensive analysis of different plausible evolutions of droughts throughout the twenty-first century over Iberia on a monthly basis, featuring three different emission scenarios (RCP2.6, RCP4.5, RCP8.5). A multi-variable, multi-model EURO-CORDEX weighted ensemble is used to assess future drought conditions using the SPI (Standardized Precipitation Index) and SPEI (Standardized Precipitation Evapotranspiration Index). All indexes were computed by considering the full period, from 1971 to 2000 merged with 2011-2100 from each RCP scenario. The results clearly show that the Iberian Peninsula is highly vulnerable to climate change, indicating a significant increase in the intensity and severity of drought occurrences, even for the low-end RCP2.6 scenario. For the RCP4.5 and RCP8.5 scenarios, the increases are more pronounced and enhanced throughout the twenty-first century, from 3 up to 12 more severe droughts for the shorter timescales with increases in mean duration above 30 months for the longer accumulation periods. The use of all the RCPs data pooled together with a multi-variable weighted ensemble approach allows not only a more accurate and robust projection of future droughts but also ensures comparability among the projections from the three RCP scenarios. The future drought evolution aspires to assist the new Portuguese national roadmap for adaptation for the twenty-first century, bridging the water sector challenges from mitigation to adaptation in a dynamic way.