降雨时程分布对山洪灾害预警影响初步研究

由降雨时间分布的不均匀性带来的流域产流峰值的变化较大,在同一个流域,成灾流量及其它条件相同,但降雨过程不同,所需要的临界降雨量是不同的。因此,山洪灾害预警实践中,通常会因为实际的降雨过程与拟定山洪灾害预警指标所依据的雨型不一致而导致预警不准确。以云南省云县爱华镇田心村下轻木林和涌宝镇涌宝村岔河两个典型小流域为研究对象,构建雨量时程分布不均匀程度计算模型,以介于-1,1]的无量纲不均匀系数表示降雨的时程分布特性,分析降雨时程分布不均匀系数与临界雨量的相关关系。结果表明:不均匀系数介于-0.8~0.8之间的14种雨量分布模式所引起的临界雨量变化在6.3%~29.6%之间,降雨时程分布越不均匀,临界雨量越小,其中主雨峰偏后的更为明显,说明流域降雨时程分布对山洪灾害预警影响显著。因此在山洪灾害预警实践中应根据实际的降雨过程对预警指标适当修正。

Influence of rainfall temporal distribution on critical rainfall for early warning of flash floods

The nonuniform temporal distribution of rainfall has significant influence on runoff crest value, and even in the same basin and under the same conditions, the critical precipitation for flash floods early warning is different due to various rainfall process. Therefore, during the practice of flash floods early warning, it often leads to inaccurate warning because the previously designed rainfall pattern is inconsistent with the actual rainfall process. Taking two small typical basins as examples, Xiaqingmulin Watershed where Tianxin Village is located, Aihua County and Chahe Watershed where Yongbao Village is located, Yongbao County of Yunnan Province, we analyzed the correlation between nonuniform coefficient of rainfall temporal distribution and critical precipitation. In the calculation, the nonuniform degree of rainfall temporal distribution was manifested by dimensionless nonuniform coefficient between［-1,1］by a calculation model. The results showed that in the built 14 rainfall distribution patterns, the nonuniform coefficients range from -0.8 to 0.8, the critical rainfalls vary in a range of 6.3% to 29.6% in the same basin. The more nonuniform temporal distribution of rainfall is, the smaller critical precipitation is, and the rain peak lags behind more obviously, indicating that the rainfall temporal distribution has a significant impact on the early warning of flash floods. Therefore, in the flood warning practice, we should adjust early warning index based on the actual rainfall process.