暴雨山洪灾害预警指标计算方法比较研究

Affected by steep geomorphology and intensive rainfall, mountain rivers are characterized by steep rise and fall hydrograph, greatly shortening the response time of residents along the river and posing great challenges to the high-precision early warning and forecasting of flash floods. Flash flood early warning is an important part of non-structural measures for disaster prevention and damage reduction and is commonly divided into water level early warning and precipitation early warning. Since the flood period is extremely short in small-sized basins where automatic monitoring stations cannot cover all the areas, the water level early warning is unpopularly used in China. The early warning based on rainfall threshold calculated by the water level/flow inversion method often misses the event due to the same frequency assumption of the rainstorm and flood, which cannot meet the actual need of mountainous flash flood prevention. To improve the early warning accuracy and increase the warning advance time of flash floods, two new methods of calculating the early warning indicators are proposed, based on methods of the rising rate in flood level and real-time accumulated precipitation. Taking the "8·16" flash flood disasters in Zhongdu River Basin (a tributary of Jinsha River in Sichuan Province) as an example, the early warning indicators are calculated by the above-mentioned methods, and the calculated results are compared to each other regarding the early warning accuracy and advance time. The results show that the early warning accuracy of inversion on water level/flow is limited in achieving the expected early-warning effect. The early warning accuracy based on the method of flood rising rate is higher. However, the early warning period from the stage rise to the peak is found to be affected by the flash flood characteristics and is relatively short. The method based on the real-time accumulated precipitation issues every alarm and prolongs the warning advance time of flash flood effectively. In addition, if the minimum 30 minutes flood warning advance time is required, the two new methods can extend the warning time by at least 30%. In conclusion, setting the threshold of accumulated rainfall combined with the rising rate of flood for disaster early warning is suggested to improve the early warning accuracy of flash flood disaster.