Assessing Hydroclimatic Extremes in the Iberian Peninsula Under Future Emission Scenarios

Hydroclimatic extremes are projected to intensify across the Iberian Peninsula (IP) under future climate change, challenging water resources, agriculture, and ecosystems. This study evaluates future conditions using mean precipitation plus three precipitation-based indices: Consecutive Dry Days (CDD), number of dry spells (CDDn), and R95pTOT (Very Wet Days). Projections used a high-resolution CHELSA-ISIMIP3b CMIP6 ensemble under three Shared Socioeconomic Pathways (SSP1–2.6, SSP3–7.0, and SSP5–8.5) and three future periods (2041–2060, 2061–2080, and 2081–2100). A hydroclimatic stress framework based on historical CDD and the fraction of the R95pTOT quintiles was applied at grid-cell and watershed scales. Precipitation declines substantially under SSP5–8.5 across southern and interior basins, exceeding 30% by 2100. Simultaneously, CDD is projected to increase, surpassing 90 consecutive dry days per year in parts of southern Iberia, whereas CDDn is projected to increase mainly across eastern and northeastern Iberia, while remaining stable or decreasing locally in southern regions. Projections of the fraction of R95pTOT indicate increasing precipitation concentration, especially across Mediterranean and southeastern regions. Combined hydroclimatic stress expands markedly under stronger forcing: by 2081–2100 under SSP5–8.5, the “Very High” class covers approximately 97% of the Guadalquivir, 95% of the Guadiana, and 65% of the Tagus basins. In contrast, the Douro shows a more moderate intensification, while the Ebro remains outside the “Very High” combined-stress class, although approximately 19% of its area reaches “High” stress. These findings identify river basins where the spatial coexistence of increasingly prolonged dry conditions and greater precipitation concentration may pose growing hydroclimatic challenges, providing a basis for basin-scale water-resource planning and climate adaptation.