Meteorological drivers modulate evapotranspiration trends under climate warming in Northeastern Spain

Abstract Climate change threatens crop productivity and water management in Mediterranean agriculture through rising temperatures, recurrent droughts, and shifting atmospheric conditions. Although warming trends are well documented across Spain, their impact on evaporative demand and irrigation remains uncertain due to the multivariate controls on evapotranspiration. Reference evapotranspiration (ET O ) and its drivers were evaluated using both a temperature-based formulation (Hargreaves-Samani method) and a physically based method (FAO Penman-Monteith ET O (FAO-PM ET O ) equation). Daily data (2004–2024) from 45 automated weather stations of the SIAR network in Aragón (NE Spain) were analyzed at multiple temporal scales using the Mann-Kendall test and Sen’s slope estimator. Crop-specific analyses for maize and representative fruit crops employed growing degree day models to define phenological stages and estimate crop evapotranspiration (ETc). Results indicate widespread and significant warming trend (mean + 0.08 °C yr⁻¹), exceeding rates previously reported. Relative humidity increased at nearly half of the stations, wind speed declined at 75% of sites, and solar radiation decreased locally, while precipitation showed no significant trend. Consequently, thermally driven ET O increased across most of the region, whereas physically based FAO-PM ET O and ETc exhibited predominantly non-significant or slightly negative trends. Compensating shifts in radiative, aerodynamic, and moisture-related drivers offset temperature increases, decoupling evapotranspiration from warming. Accelerated crop phenology further stabilized cumulative seasonal ETc. These findings demonstrate that rising temperatures alone do not necessarily increase evaporative demand or crop water use, highlighting the limitations of temperature-based irrigation projections and the need for multivariable, physically consistent assessments of climate change impacts on regional agricultural water requirements.