Long-term monitoring of surface water dynamics using remote sensing data: A case study of Al Wahda dam, Morocco

Al Wahda Dam, located in northern Morocco, is one of the country's most strategic hydraulic infrastructures, with a storage capacity exceeding 3 billion cubic meters. It was constructed in 1997 to ensure agricultural irrigation in the Gharb plain, provide flood protection, and regulate hydrological flow in the region. However, the performance of this structure has been increasingly affected by rainfall deficits and the growing demand for irrigation water. In addition, rising temperatures have increased evaporation losses, particularly during the summer, thereby reducing the effective storage capacity. This study aims to monitor the spatiotemporal evolution of the Al Wahda dam using the NDWI index derived from remote sensing data. It also seeks to highlight the impact of rainfall variability on the dam by calculating the SPI. The findings suggest that during wet years, the water surface area increases significantly (110 km2 in 1998), whereas during dry years, a marked contraction of this surface is observed (72 km2 in 2016). The statistically significant correlation (p-value < 0.05) between the dam's water surface area and the SPI-12 indicates the influence of climatic conditions on its dynamics.