Impact of LULC changes on small watershed morphometry and delineation of sustainable conservation strategies for degraded transboundary rivers

Small streams in the large river basins are disappearing, and there is no update on their historical and current morphometric status. Field inventory and visual inspections quantified the impact of land use and land cover (LULC) change on the reference year morphometry (1970-1977) of seven watersheds and fifty-six subwatersheds, using drone imagery and Global Positioning System-based ground control points to refine the reference map and generate the current map (2021-2024). The decreasing stream number (Nu), stream length (Lu), and drainage density (Dd) (1) explained the mechanism of disappearing and shrinking large rivers; (2) classified seven watersheds and fifty-six subwatersheds into near threatened (NT), vulnerable (VU), endangered (EN), critically endangered (CR), and extinct (EX) categories; and (3) emphasized rejuvenation of 9,84,068 km of lost streams to restore Dd ≥ 2 km/km² in the Ganga River basin (GRB). From these empirical estimates, the UN's commitment to restoring 300,000 km of degraded rivers thus needs ~ 150,000 km² of watershed area to delineate ex-situ and in-situ restoration and conservation of disappearing three intrinsic morphometric attributes, i.e., Nu, Lu, and Dd.