Hypsometric control on surface and subsurface runoff

A fundamental problem in hydrology is relating the basin hydrological response to the geomorphologic properties of a catchment. In this technical note, we show that the hypsometric distribution exerts control on surface and subsurface runoff partitioning by isolating its effect with respect to other basin characteristics. We conduct simulations using a distributed watershed model for hypsometric realizations developed by modifying the contour line values of a real basin. Results indicate that the runoff components are a function of the basin hypsometric form. In general, a relatively less eroded (convex) basin exhibits higher total runoff that is more dominated by subsurface processes, while a relatively more eroded (concave) basin shows less total runoff with a higher fraction of surface response. Hypsometric differences are also observed in the relations between base flow discharge and the mean groundwater depth and the variable source area. Furthermore, the hypsometric form reveals clear signatures on the spatial distribution of soil moisture and runoff response mechanisms.