Tracking Dynamic Regimes and Ecological Functions of Surface Water in the Niger-Lake Chad Basins through Multi-Source Fusion (2015–2024)

Accurate long-term monitoring of surface water dynamics in the Niger River and Lake Chad basins is crucial for regional ecological security and sustainable water resource management. However, such monitoring is often hindered by insufficient continuous high-frequency observations—necessary to capture rapid shifts between permanent and seasonal water bodies in semi-arid transition zones—as well as by persistent cloud cover. To address these limitations, we developed a spatio-temporal data fusion framework designed to delineate detailed evolutionary patterns and regime shifts in surface water. Our methodology integrates Sentinel-1 SAR, Sentinel-2 optical imagery, and digital elevation model (DEM) data, adopting a “zoning modeling” strategy to reduce sensor-specific biases and environmental noise, thereby producing annual and seasonal surface water distribution maps. Furthermore, we developed a pixel-level, climate-coupled model based on inundation frequency to quantify changes in the extent, timing, and type of water bodies across a multi-year time series. Integration of these outputs elucidated the spatial heterogeneity of water resources throughout the study region from 2015 to 2024. Validation using randomly distributed reference samples demonstrated strong consistency, with overall accuracy exceeding 90%, confirming the robustness of our framework. Through an ecology-oriented classification scheme, we identified permanent water bodies—largely concentrated in the southern reaches of the Niger River main channel and the central zone of Lake Chad—as serving a “core support” function within the ecosystem. In contrast, seasonal water bodies followed a “dense in the south, sparse in the north” spatial pattern and acted as critical “ecological buffers” for arid northern areas. Notably, seasonal water extent expanded significantly during high-rainfall years such as 2018 and 2022, underscoring its pronounced sensitivity to climatic variability. Compared with current state-of-the-art approaches, the proposed framework enables characterization of high-frequency surface water dynamics and associated ecological interactions as continuous spatio-temporal fields, thereby providing a reliable and scalable tool to inform sustainable watershed management strategies across Africa.