Evaluation of CMIP6-based climate projections in Northern Morocco: A bias corrected assessment of temperature and precipitation trends in three mediterranean watersheds

Northern Morocco, with its Mediterranean climate and complex topography, faces severe climate change vulnerability, with direct implications for water security and agricultural sustainability. This study evaluates historical (1987–2014) and future (2015–2100) climate trends across three strategic watersheds, Oued Laou, Kalaya, and 9 Avril, using high-quality observational data from the Loukkos Hydraulic Basin Agency (LHBA) and CMIP6 Global Climate Models (MPI-ESM1-2-HR and GFDL-ESM4). To address systematic GCM biases, the Quantile Delta Mapping (QDM) method was applied to each climate scenario. Statistical analysis using the Mann-Kendall test and Sen’s Slope estimator revealed a significant historical warming trend, particularly in summer and autumn. Future projections under three Shared Socioeconomic Pathways (SSP2.6, SSP4.5, and SSP8.5) indicate a steady temperature increase, with a projected rise of 2.5–3.5 °C by 2100. Under the high-emission scenario (SSP8.5), Sen’s Slope confirms an annual warming rate of up to +0.059 °C/year and a progressive decline in annual precipitation of up to 30 % (specifically -2.12 mm/year for Oued Laou). Validation against observations (2015–2022) demonstrated high model fidelity for temperature, with an average Kling-Gupta Efficiency (KGE) of 0.880 and a correlation (r) of 0.96. For precipitation, the models effectively captured regional variability, with average KGE scores ranging from 0.469 to 0.538, despite inherent topographic complexity. A comparative analysis across the basins identifies the Oued Laou watershed as the most sensitive to future aridification. In contrast, the 9 Avril watershed poses greater simulation challenges due to its inland topographic features. This research provides a critical high-resolution dataset for hydrological modeling and supports the development of climate-resilient management strategies for water and agriculture in Northern Morocco.