Influence of open-source topographic data on basin-scale flash flood modelling in High Mountain Asia

Study region A mountain basin in southern High Mountain Asia (HMA).

Study focus HMA is susceptible to flash flood hazards, while the difficulty of topographic data acquisition challenges its flash flood modelling. Little attention has been paid to the influence of open-source topographic data on flash flood modelling in the region. In this study, the influences of four open-source topographic data used widely on flash flood modelling were explored.

New hydrological insights for the region Results indicated significant influences of these open-source topographic data. The 30-m ASTER GDEM data with unreasonable results were not recommended. At the basin scale, results from 30-m SRTM, 12.5-m ALOS PALSAR and 30-m COP DEM data underestimated the maximum flood depth by −16.04% ∼ −5.18%, and 30-m COP DEM data underestimated the maximum flood extent by −3.51% ∼ −4.63%. The simulated maximum flood velocity and hydrodynamic force, as important disaster-causing mechanisms of flash floods, exhibited biases of −16.38% ∼ 11.92% and −99.46% ∼ −5.87%, respectively. At three infrastructure sections concerned, different qualities of three open-source topographic data caused inconsistent biases. The simulated temporal characteristics of the above indicators were consistently delayed by 1.23∼180.22%. Such biases have significant influences on data-scarce basins in HMA, causing underestimated flash flood risk and delayed early warning. In-depth studies of topographic data fusion and bias correction are suggested to improve flash flood modelling.