Convection-Permitting Regional Climate Simulations Reveal Stronger Drying and Snow Loss in Semi-Arid Mountainous Basins of Morocco

Abstract

Mountainous basins in semi-arid regions are among the most climate-sensitive environments, yet their hydro-climatic processes remain poorly represented by regional climate models. This study provides the first hydrological evaluation of a convection-permitting regional climate model (WRF3) with a spatial resolution of 3 km in mountainous basins of Morocco in North Africa, using a multi-model hydrological framework (HYPE and GR4J-CemaNeige). Results show that hydrological simulations forced by the convection-permitting WRF3 model provide a better agreement with observed streamflow and a set of different hydrological signatures than those forced by the coarser, convection-parameterized WRF20 model (20 km). Under the SSP5–8.5 scenario, the projections indicate precipitation decreases of 31%–62%, increases in potential evapotranspiration of 16%–27%, and streamflow reductions ranging from 64%–87%, depending on the climate forcing (WRF3 versus WRF20). There is a systematically stronger reduction in water resources in WRF3 projections than in WRF20 that is consistent across different basins. Snow contributions decline more strongly in simulations forced by the convection-permitting regional climate model (WFR3), leading to a shift from a snow-dominated to a predominantly rain-dominated hydrological regime. These results highlight the added value of high-resolution climate modelling in capturing fine-scale mountain processes, strengthening the confidence in climate-impact assessments, and also reveal the severe vulnerability of semi-arid mountainous water resources to future warming. The more pessimistic scenarios obtained with the convection-permitting regional climate model call for a reassessment of currently available scenarios for future water resources in semi-arid mountainous regions obtained with coarse resolution climate models.