Historical climate maps of drought indices from 1990-2025 for the Guadalquivir basin (Spain)

Historical climate maps of drought indices for the Guadalquivir river basin and the Los Pedroches region (Andalusia, Spain) between the years 1990 and 2025. Maps show the Standardized Precipitation Index (SPI) and the Standardized Precipitation-Evapotranspiration Index (SPEI) at different time scales (3, 6, 9, 12 and 24 months). SPI is a widely used index to quantify meteorological drought conditions. It is based exclusively on precipitation data and allows for the evaluation of humidity anomalies. Negative SPI values indicate drier-than-normal conditions, while positive values indicate wetter conditions. The SPI allows for the comparison of drought conditions between regions with different climate regimes. SPEI expands upon the SPI concept by also incorporating atmospheric water demand, that is, potential evapotranspiration (PET), which depends primarily on temperature. This allows for a more comprehensive assessment of the water balance, especially useful in the context of climate change, where rising temperatures can intensify drought even without a significant decrease in precipitation. SPEI is also calculated at different time scales (3, 6, 9, 12, and 24 months) and uses a methodology similar to the SPI, but applied to the water deficit (precipitation minus PET).