Projected Increases in Population Exposure to Droughts in the Iberian Peninsula under 1.5 and 2C Global Warming Levels

Increasingly frequent and intense drought events at a global scale emphasize the heightened vulnerability and exposure of ecosystems and human populations. In Southern Europe, identified as a significant climate change 'hotspot', particularly within the Iberian Peninsula (IP), droughts are a recurring and impactful type of extreme weather events. Anticipated shifts in climate patterns and the occurrence of extreme weather events are expected to cause profound environmental and socio-economic consequences. This study investigates the impacts of 1.5 and 2C Global Warming Levels (GWL) at the end of the 21st century on drought events and population exposure to dry extreme events in the IP. For this research, EURO-CORDEX experiments (13 simulations) were considered and aggregated as a weighted multi-variable multi-model ensemble, encompassing different time periods, namely the historical period from 1971 to 2000, 30-year periods centred on the 1.5 and 2C GWL years, and the projected end of the century period spanning 2066 to 2095. Two drought indicators, the Standardized Precipitation Index (SPI) and the Standardized Precipitation-Evapotranspiration Index (SPEI) are used to characterize droughts. Three representative scenarios are employed to delineate distinct greenhouse gas emission trajectories. This study uses Eurostat's demographic projections covering the period up to 2100 with 5-year intervals starting in 2020 for Portugal and Spain. The study supplements historical population values with The World Bank data until 2011. For the RCP8.5 scenario, changes in the number of moderate, severe, and extreme droughts are projected to grow throughout the century, with 24 to 33 % (58 to 69 %) in the case of SPI (SPEI). This escalation reflects an overwhelming growth of drought occurrences in the IP because of the 0.5C additional warming. Population exposure to extreme droughts is higher under the 2C scenario than under the 1.5C scenario, particularly as measured by SPEI, reflecting again the importance of the expected increase of the temperature in the IP. Population exposure to extreme droughts in the end of the century can vary between an increase of 50 % and more than 600 % for SPEI with timescales of 3 to 12-months under RCPs 4.5 and 8.5. The findings of this study reveal a notable projected surge in population exposure to droughts throughout the entire IP, particularly by the end of the century, with climate change identified as the predominant factor for this escalation. The findings underscore the urgency for regional authorities, policymakers, and society to prioritize adaptation planning and develop a comprehensive understanding of the vulnerabilities and potential strategies to cope with the challenges posed by dry extreme events. This work was funded by the Portuguese Fundao para a Cincia e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). This work was performed under the scope of project https://doi.org/10.54499/2022.09185.PTDC (DHEFEUS) and supported by national funds through FCT. DL and AR acknowledge FCT I.P./MCTES (Fundao para a Cincia e a Tecnologia) for the FCT, 2022.03183.CEECIND/CP1715/CT0004 (https://doi.org/10.54499/2022.03183.CEECIND/CP1715/CT0004) and (https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006 (Complex), respectively.