基于全国山洪灾害调查评价获取的山洪灾害防治断面临界雨量数据，依据流域产汇流原理充分考虑前期影响雨量Pa、临界雨量P和预警时段H对复合预警指标的不同影响，提出了由临界雨量推求复合预警指标的公式，并以江西婺源县为例说明了该公式的可行性及其应用过程，提出了一套完整的山洪灾害预警方案。结果表明：婺源县复合预警指标值的平均极差为5.4，平均变差系数为0.029，由临界雨量推求复合预警指标可行。将降雨开始时的前期影响雨量、实测或预报的雨量及其时段长代入公式得实时复合预警指标值，再与断面复合预警指标阈值比较，达到或超过预警阈值即发布山洪预警，否则根据后续降雨情况重新判断是否预警。该方法充分利用事发之前的已有信息，能计算任意时段预警值，可为山洪灾害预警提供一种新的有效方法。

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.

国家重点研发计划( 2016YFA601504) ；2017“全国典型类型区小流域复合预警指标特征与规律分析”山洪灾害防治项目；中央高校基本科研业务费专项资金 (2017B10214)