A modified TOPMODEL introducing the bedrock surface topographic index in Huangbengliu watershed, China

Subsurface stormflow is a dominant runoff mechanism in steep humid mountainous areas. An insite measurement of subsurface stormflow suggests that the bedrock surface plays an important role in the runoff generation and routing process, which was rarely adopted in hydrological modelling studies. To improve the runoff simulation performance, the bedrock surface topographic index is introduced, and a modified TOPMODEL based on the bedrock surface topographic index is developed to simulate the runoff. The modified TOPMODEL is applied to the Huangbengliu (HBL), a steep watershed in Gongga Mountain, and proved to be more appropriate for the HBL watershed, especially for peak simulation. The Nash-Sutcliffe model efficiency (NSE) is improved from 0.24 to 0.58 in the calibration period and from 0.40 to 0.62 in the verification period. The result of this study can advance the understanding of the mechanism of flash floods and contribute flood control and disaster prevention in the HBL watershed and similar areas.