Climate Change Impacts on Mediterranean Grassland Productivity Along a Climatic Gradient in Central Spain: An Ecohydrological Modeling Approach

Mediterranean grasslands are highly sensitive to climate variability because their productivity is strongly constrained by water availability. Understanding how future climate change may affect forage production across hydroclimatic gradients is essential for the adaptation of extensive grazing systems. This study evaluated the response of Mediterranean grassland productivity to future climate scenarios along a climatic gradient in central Spain using the ecohydrological model SIMPAST driven by an ensemble mean of six CMIP6 global climate models under four Shared Socioeconomic Pathways (SSPs). Three representative grassland systems located in mountain, foothill, and semi-arid flatland environments were characterized according to vegetation composition, soil properties, and historical biomass production. The model was calibrated using productivity data from 2016 to 2023 and independently validated with biomass observations from 2024 to 2025. Calibration focused on radiation use efficiency and water use efficiency parameters, achieving high agreement between simulated and observed biomass (R2 = 0.90) with calibration absolute errors below 20 kg DM ha−1 across the three study sites. Independent validation using biomass observations from 2024 to 2025 resulted in RMSE values ranging from 506 to 771 kg DM ha−1. Simulations revealed clear spatial differences in future productivity responses. Mountain grasslands exhibited stable productivity throughout most of the century, with projected biomass reductions of approximately 4% and increases in interannual variability of 14% under SSP5–8.5 relative to the historical period. In contrast, foothill grasslands showed moderate productivity declines (25%) and higher variability (37%), while semi-arid flatland systems revealed the strongest reductions in biomass production (33%) together with the largest increase in interannual variability (72%). These results indicate that arid environments are considerably more vulnerable to future climatic stress due to stronger water limitations. Simulations also suggested increasingly variable and less predictable forage availability under future climate conditions, particularly under higher-emission scenarios. Overall, the findings highlight the central role of water availability in regulating Mediterranean grassland productivity and demonstrate the usefulness of ecohydrological models for supporting adaptive grazing management and climate change adaptation in Mediterranean livestock systems.