Abstract
<title>Abstract</title> <p>Remote sensing techniques have become crucial for monitoring environmental changes, evaluating land cover variations, and assessing varied agricultural ecosystems by systematically gathering spectral data from a distance. The lower portion of the Ganges and Brahmaputra (GB) river basin, the study area, comprises a complex, dynamic, and significant land cover. For greater accuracy and reduced bias, this study investigated 14 vegetation and water-drought reflectance indices (VIs and WDIs) to monitor and measure long-term variations in land status. The classification, dissimilarities, and correlations of the spectral index were examined. The long-term weather events, hydrometeorological data, and previous studies of the same geographical pattern justified the findings of this exploration. The class values (land area) of the VI and WDI maps revealed that surface water bodies decreased 35–45% throughout the last 20 years in the lower GB basin. Among the field classes of indices, the built area increases significantly (60–80%), while the vegetation canopy and cultivable land increase by 30–40%. The WDI values indicated that drought events rose by 30%, with the streamflow and water level of the GB River declining by 12–15% and 8–12% in the same duration. The LULC map (2004 and 2024) showed the same results, with a decline in the green forest from 12% to 7%. Satellite imagery of water occurrence change intensity illustrated that around 15% of the water of the GB river system was lost and 12% shifted within the last 20 years. This study presented a complete and valid picture of the land status, which helps to understand and monitor vegetation, water, drought, and built-up conditions in such dynamic geographic regions. Policymakers will follow the findings of this study for decision-making and sustainable development.</p>