Global projections of aridity index for mid and long-term future based on CMIP6 scenarios

Abstract. This study evaluates and projects global aridity index (AI) and dryland distribution using the FAO Aridity Index based on Penman-Monteith potential evapotranspiration. A multimodel ensemble of 13 CMIP6 models, with a horizontal resolution of 100 km, was selected for analysis. The ensemble was validated against WorldClim and ERA5 reanalysis datasets for the reference period (1970–2000), showing strong correlations in key variables and consistent geographic representation of drylands, with some regional discrepancies, notably in North-Eastern Brazil. Future projections of AI were generated for three socio-economic pathways (SSP2-4.5, SSP3-7.0, and SSP5-8.5) and two timeframes (2030–2060 and 2070–2100). Results indicate that most regions will maintain their current climate classification but face decreasing AI values, signifying drier conditions. Under SSP2-4.5 and SSP5-8.5, significant drying is projected for the mid-term, with continued but slower changes by century's end, affecting regions such as North and Central America, the Mediterranean Basin, and areas adjacent to present-day deserts. In contrast, SSP3-7.0 shows limited drying or localized wetting in the mid-term, followed by extensive drying in the long-term. Comprehensive maps and tables detailing dryland proportions and distributions are provided to support these findings.