A simulation study of flash floods in small watersheds based on the combined effects of future land use change and extreme rainfall

Abstract Watershed hydrology is influenced by the subsurface of the watershed and the intensity of rainfall. The impact of rapid land use changes and frequent extreme rainfall on watershed flooding is uncertain. In this study, the PLUS model was used to simulate land use scenarios for 2020, 2030 and 2040, and the spatial pattern of simulated land use in 2020 was validated against the spatial pattern of actual land use in 2020. An initial hydrological model was constructed, and the hydrological model was validated and evaluated using historical rainfall events. Based on three land use scenarios, three rainfall return periods and three rainfall peak ratios, the runoff and inundation results under 27 scenarios were simulated by coupling the hydrological model with the hydrodynamic model. The results showed that changes in land use induced changes in rainfall runoff and flood inundation, and that the inundated area of the watershed decreased and the depth of inundation increased as the impervious surface area increased in the future. However, rainfall intensity has a more profound effect on watershed flooding than land use, where the effects of rainfall peak ratio and rainfall return period changes are 5 and 14 times higher than land use changes, respectively. The Kappa coefficient validated by the land use simulation experiment reached 85.7%, and the Nash coefficient validated by the hydrological model was generally higher than 69%. This study explored the impacts of land use change and rainfall intensity on watershed flooding from both future and extreme perspectives, and explored the characteristics of watershed flood response under multi-scenario modeling by constructing a more complete and scientific modeling framework, providing a new perspective for flood simulation studies.