This paper seeks to revisit that occasional paper of 1989, and expand its scope in two ways: one, the earlier paper covered “the role of forest and land use” and the effects of surface erosion. We have added two more factors – the impacts of climate change, and the development of infrastructure, on water availability downstream. Two, the earlier document only covered the Ganges and Brahmaputra basins; we also include the Indus River basin in our study.