Fog is a vital moisture source in fog-dependent drylands. In coastal, foggy deserts, ocean-generated fog, formed from oceanic moisture, is widely recognized as the dominant fog type. However, locally generated fog, formed from water vapor released through evapotranspiration, is often overlooked despite its potential contribution to fog formation. Our understanding of spatiotemporal fog origins remains limited due to the scarcity of integrated ground and satellite observations across space and time. Here, we establish a new framework that integrates isotope- and satellite-based observations to identify the spatiotemporal origins of fog by analyzing its moisture composition and evolution patterns. A unique decade-long fog isotope dataset (2014–2023) from Gobabeb within the Namib Desert was integrated with ground-validated satellite-derived fog detections over the central Namib Desert (2020–2023). Our results indicate that the proportion of locally generated fog derived from isotope and satellite data aligns well across the central Namib Desert at a broad regional scale. At Gobabeb, isotope-based analyses reveal an increasing trend in locally generated fog from 2014 to 2023, highlighting its growing importance as a moisture source in the region. Spatially, satellite-based observations indicate a significant decrease in locally generated fog from the coast to inland areas and from north to south across the central Namib Desert between 2020 and 2023 (p < 0.01). Our new framework provides comprehensive and critical insights into climatological and spatiotemporal assessments of fog origins in the context of global warming.