Surface water monitoring in Ghana: Evaluating spectral water indices across diverse aquatic environments

Reliable surface water monitoring is essential for sustainable water governance, yet detecting rivers and lakes in mining-impacted tropical landscapes remains challenging. Here, we present a multi-sensor, index-based remote sensing framework to evaluate surface water extraction across Ghana using Landsat and Sentinel-2 imagery. Five widely used spectral water indices, AWEI, MNDWI, NDWI, NWI, and WRI, were systematically implemented within a cloud-based processing environment to assess their performance under heterogeneous land-cover conditions influenced by sedimentation and anthropogenic disturbance. All indices successfully detected major water bodies, including Volta Lake and Lake Bosomtwe; however, substantial differences emerged in river delineation. AWEI and MNDWI consistently outperformed conventional ratio-based indices, achieving kappa coefficients of 0.83–0.95 and overall accuracies ranging from 0.79 to 0.88 across both sensors. NDWI showed moderate performance, while NWI and WRI exhibited higher omission errors for narrow and turbid rivers despite relatively high overall accuracies. Cross-sensor comparison revealed that Sentinel-2 performed best for large, spectrally distinct water bodies, whereas Landsat more effectively captured narrow and hydrologically connected river networks. These results demonstrate that spectral sensitivity and index–sensor compatibility exert greater influence on detection accuracy than spatial resolution alone. The core contribution of this study lies in providing empirical evidence that index selection is more critical than sensor choice for reliable surface water monitoring in mining-disturbed tropical environments. By integrating quantitative accuracy assessment with governance-relevant interpretation, the findings offer actionable guidance for scalable, open-access water monitoring systems that support regulatory enforcement, environmental accountability, and sustainable water resource management in Ghana and comparable resource-limited regions.