Numerical simulation and validation of heavy rainfall flood inundation in small watersheds in undocumented mountainous areas

With global warming and the increase in extreme precipitation events,floods are becoming more frequent in mountainous areas, and thesafety of lives and property of people is seriously threatened. However, understanding of theflooding process in uninformative mountainousareas is limited due to the lack of high-quality hydrometeorological data. Hence, this study adopts the MIKE21 model to simulateflood inun-dation in the Shadai River basin in the Qilian Mountain region of the northern Tibetan Plateau as an example. This validates the model-simulatedflow and inundation extent using theflow data obtained from the calculation of theflood trace points, extent of inundation,and high-resolution remote sensing images. The results show that theflashflood inundation mainly occurs at 12:00-01:00 AM on 18August 2022, and the simulated and actual maximum inundation areas are 7.9 and 9.5 km2, respectively. ThefittedF-statistic value is0.81, and the relative error between the calculatedflow rate of theflood trace point and the model-simulatedflow rate is 8%, indicatinggood consistency. Furthermore, an in-depth exploration of the model parameter sensitivity reveals that the use of distributed Manning'sroughness coefficient value has higher simulation accuracy.