A Satellite-Based Climatology of Fog and Low Stratus to Support Nature-Based Water Harvesting in Arid Areas of Morocco

 In arid and semi-arid landscapes like many areas in Morocco, addressing water scarcity requires innovative nature-based solutions (NbS). Fog and Low Stratus (FLS) clouds constitute a major atmospheric feature in Morocco, simultaneously representing a significant hazard for air, maritime, and road transportation and a valuable nature-based water resource for arid and semi-arid ecosystems through fog-water harvesting. However, effective implementation of such NbS depends on precise identification of viable locations and optimal collection periods. In a country characterized by strong climatic heterogeneity and limited ground-based observations, satellite remote sensing provides a critical means for assessing the spatial and temporal availability of this underutilized water source under current and future climate variability. This study introduces a novel nighttime FLS detection algorithm specifically designed for Morocco’s diverse climatic regimes, using only infrared observations from the Meteosat Second Generation (MSG) SEVIRI instrument. Hourly satellite data spanning 2020–2024 were processed to produce the first high-resolution, national-scale climatology of FLS occurrence over Morocco. Designed for the region's heterogeneous climates, the tool provides essential monitoring for assessing NbS potential. The algorithm was systematically validated using coincident hourly SYNOP observations from the Moroccan Directorate General of Meteorology network. Validation results demonstrate reliable performance, with a probability of detection exceeding 54%, a false alarm ratio close to 45%, and a frequency bias generally within 1.4. The resulting climatology reveals two major coastal hotspots of persistent FLS occurrence along Morocco’s Atlantic façade, in the Northwest and Southwest, both exhibiting pronounced seasonal and diurnal cycles. These regions coincide with areas of high potential for fog-water harvesting, offering a climate-resilient, nature-based solution to enhance water availability in water-stressed environments. These findings directly inform hydrological planning by pinpointing areas where fog harvesting projects are most likely to be effective and resilient. By providing spatially explicit and operationally robust information on FLS occurrence, this study supports the integration of satellite-based monitoring into the planning and upscaling of fog-water harvesting systems. The results contribute to broader NbS strategies aimed at improving water security, supporting ecosystem services, and strengthening climate adaptation in arid and semi-arid landscapes.