Flow regime characteristics of Himalayan river basins in Nepal

A large-scale perspective on the nature and geography of Himalayan river flow regimes across Nepal is provided using mean monthly flow data for 36 river basins. A classification approach is used to group annual regimes according to their "shape" and "magnitude". The results suggest that the timing and length of the monsoon control "shape" regime and precipitation amount determines the "magnitude" regime. For regime "shape", July-September peaks are typical of central basins at lower altitudes; July-August peaks are characteristic of central basins at moderate to high altitudes and eastern higher mountains; and August peaks are confined to western basins and higher mountains. Low, intermediate and high "magnitude" regime classes correspond with basin rainfall totals; and their distribution is explained by decreasing rainfall gradients from east to west and from south to north. Localized pockets of classes exist possibly due to the affect of topography on rainfall and basin characteristics in the controlling regime.