Assessing groundwater storage response to snow cover dynamics in large Moroccan river basins over the last decades using remote sensing data

Groundwater reserves face increasing pressure from human activities and climate variability. Increased domestic, industrial, and agricultural demand has led to unsustainable dependence, disrupting natural replenishment, particularly in semi-arid and arid regions. This study examines how snow cover, a key factor in groundwater recharge, influences groundwater reserves in Morocco's main basins, focusing on assessing the relative importance of snowmelt and rainfall. Remote sensing data from MODIS for snow cover area (SCA), the Global Gravity- based Groundwater Product (G3P) for groundwater storage anomalies (GWSA), and the Integrated Multi-satellitE Retrievals for GPM (IMERG) for rainfall were used for this purpose from September 2002 to August 2023. Trend analysis, correlation metrics, and a regression-based framework were used to assess temporal variability and quantify recharge sources. Results showed that G3P-derived GWSA accurately captured groundwater level variations, achieving high correlation (up to 0.93) and low error (as low as 0.72), confirming its reliability. During the study period, most basins showed significant GWSA declines, closely related to decreasing SCA. A 6 to 8-month lag was observed between SCA and GWSA peaks. Furthermore, SCA depletion and GWSA change rates revealed distinct hydrological responses across basins. In Oum Er-Rbia and Draa, their strong correlation highlighted the significant role of snowmelt in groundwater recharge. In contrast, moderate correlations in other basins indicate additional influences. On average, snowmelt contributed 5 %–50 % to groundwater recharge, highlighting its important, yet secondary, role in seasonal snow regions. These results highlight the role of snowmelt in groundwater recharge and the vulnerability of groundwater to variations in snow cover and precipitation. Our results further underscore the need for adaptive water management, particularly in semi-arid and arid regions.