Method for deriving composite warning index based on critical rainfall and its application

This study proposes a formula for computing composite warning index according to critical rainfall based on the critical rainfall data of flash flood disaster prevention and control sections obtained from national flash flood disaster investigation and evaluation.According to principles of basin runoff yield and concentration,this formula takes into full consideration the different effects of antecedent influence rainfall(Pa),critical rainfall(P),and early warning period(H) on composite warning index.In addition, this paper takes Wuyuan County in Jiangxi Province as a case study of the feasibility and application of this formula and proposes a complete warning plan for flash flood disasters.The results show that the average range of the composite warning index threshold in Wuyuan County is 5.4,and the average dispersion coefficient is 0.029.It is feasible to derive the composite warning index from the critical rainfall.The early warning plan is as follows:first,substitute the antecedent influence rainfall at the start of rainfall,the measured or forecast rainfall and its duration into the formula to obtain the real-time composite warning index value;then compare it with the cross-section composite warning index threshold.If it reaches or exceeds the warning threshold,then issue the flash flood warning;if not,repeat the steps according to the subsequent rainfall situation.This method makes full use of the existing information before the event and can calculate the warning value at any time.So it can be a new effective method for flash flood disaster warning.

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