Abstract
Flash floods in mountainous areas have become more severe and frequent as a result of climate change and are a threat to public safety and social development. This study explores the application of distributed hydrological models in flash floods risk management in a small watershed in Sichuan Province, China, and aims to increase early warning lead time in mountainous areas. The Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) model was used to simulate the flash flood process and analyze the variation in flood hydrographs. First, the HEC-HMS model was established based on geospatial data and the river network shape, and eight heavy rainfall events from 2010 to 2015 were used for model calibration and validation, showing that the HEC-HMS model was effective for the simulation of mountain floods in the study area. Second, with the assumption that rainfall and flood events have the same frequency, the flood hydrographs with different frequencies (p = 1%, 2%, 5%, and 10%) were calculated by the HEC-HMS model. The rising limbs of the flood hydrographs were significantly different and can be divided into three parts (0–5 h, 6–10 h, and 11–15 h). The rising rate of the flood stage for each part of the flood hydrograph increases in multiples. According to the analysis of the flood hydrographs, two critical early warning indicators with an invention patent were determined in the study: the flood stage for immediate evacuation and the rising rate. The application of the indicators in the study shows that it is feasible to advance the time of issuing an early warning signal, and it is expected that the indicators can offer a reference for flash flood early warning in the study area and other small watersheds in mountainous areas.
Highlights
With the increasing frequency of extreme weather conditions, flash floods have become one of the most severe natural hazards worldwide [1,2]
By taking the variation in the flood stage stage was proposed as an early warning index before the stage station at the gauging section reaches the into account, we aim to advance the issued time of the flash flood early warning signal and increase threshold for flash flooding
By taking the variation in the flood stage into account, we aim to advance the lead time for evacuating people in danger in mountainous areas to reduce the losses caused by the issued time of the flash flood early warning signal and increase the lead time for evacuating people flash floods
Summary
With the increasing frequency of extreme weather conditions, flash floods have become one of the most severe natural hazards worldwide [1,2]. Flooding causes over one-third of the total damage and two-thirds of the impact to people affected by natural disasters, with Asia and Africa accounting for 35% and 29% of worldwide losses, respectively [3]. Water 2020, 12, 255 more than 27,000 deaths or missing persons since 1949; in addition, the deaths in mountainous areas account for over 70% of total deaths [4]. Determining the threshold for disaster prevention and damage reduction to warn the targeted people to evacuate is of the utmost importance. Critical rainfall is a type of threshold that refers to the minimum rainfall magnitude when flash floods occur in mountainous areas [5,6]
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