Rising Atmospheric Water Demand in Iberia: High-Resolution Projections of Potential Evapotranspiration and Agricultural Impacts

Potential evapotranspiration (PET) is a primary driver of agricultural water demand, yet its estimation remains uncertain in topographically complex and water-limited regions such as the Iberian Peninsula. This study develops a high-resolution, climate-driven PET framework to evaluate present and future atmospheric water demand and its implications for Mediterranean perennial agriculture. PET was calculated using the Hargreaves method from multiple climate datasets representing observations, reanalysis, and climate projections (CHELSA, E-OBS, ERA5-Land, and C3S CMIP6 Atlas) for the historical period 1981–2010. Dataset intercomparison shows that the high-resolution CHELSA product best reproduces regional climatic gradients while maintaining consistency with reanalysis products, making it suitable for impact assessment in complex terrain.

Future PET projections were analysed using CHELSA under three CMIP6 scenarios (SSP1-2.6, SSP3-7.0, SSP5-8.5) for mid- and late-21st century periods. Results indicate a robust intensification and spatial expansion of evaporative demand across Iberia, scaling with greenhouse gas forcing. Under SSP5-8.5, large areas of central and southern Iberia are projected to exceed 1400–1600 mm yr⁻¹ by the late century, while even Atlantic and mountainous regions experience unprecedented increases.

A ranking analysis of temperature, precipitation, PET, and precipitation-evapotranspiration balance at the NUTS-2 level reveals increasing climatic stress in interior regions, particularly Castilla-La-Mancha, Extremadura, Madrid, Castilla-y-León, and Centro-Portugal. To assess agricultural implications, PET was combined with FAO-56 crop coefficients to estimate crop evapotranspiration (ETc) for vineyards, olive groves, and fruit trees. All crop systems show substantial increases in water demand, with olive and fruit-tree systems in southern and eastern Iberia exhibiting the largest intensification.

These findings highlight the added value of high-resolution climate data for regional impact assessments and indicate a transition toward a more water-demanding climate across Mediterranean agroecosystems. Without adaptation measures—including improved irrigation efficiency, crop management adjustments, and strategic land-use planning—future evaporative pressure may threaten the sustainability of perennial agriculture and regional water resources in the Iberian Peninsula.