Monitoring monthly dynamics of Nile River Basin surface water by combining Sentinel-1 SAR and Sentinel-2 multispectral imagery

Study region: The Nile River Basin (NRB), a transboundary watershed spanning multiple countries in northeastern Africa, plays a critical role in the region’s water security and sustainable development. However, persistent cloud cover driven by tropical air currents and monsoonal shifts poses major challenges for consistent surface water monitoring across the basin. Study focus: This study addresses the limitations of traditional optical remote sensing in monitoring surface water under frequent cloud cover. We developed a collaborative multi-source data integration framework (CMDIF) combining Sentinel-1 radar and Sentinel-2 optical imagery to generate monthly surface water maps of the NRB at 10-meter resolution. The approach achieves mapping accuracy exceeding 94.5%, offering improved spatiotemporal consistency in detecting surface water dynamics. New hydrological insights for the region: Our results reveal distinct spatial and temporal patterns of surface water distribution across the NRB. Surface water is more abundant in the south, scarcer in the north, east, west, and concentrated in the central basin, covering an average of 10 . 28 × 1 0 4 km 2 . The largest inundation occurred in September 2020 ( 11 . 23 × 1 0 4 km 2 ), and the smallest in May 2019 ( 9 . 91 × 1 0 4 km 2 ). The Victoria Lake sub-basin holds the highest proportion of surface water at 66.86%. These findings highlight the value of integrating radar and optical satellite data for year-round monitoring in cloud-prone, data-scarce regions, enhancing understanding of hydrological variability in the NRB. • Propose a collaborative multi-source framework (CMDIF) for surface-water monitoring. • Generate monthly 10m surface-water maps for the Nile Basin with 94.5% accuracy. • Reveal spatial patterns and monthly dynamics of surface water in the Nile Basin.