基于降雨-径流长期观测的山洪响应特征分析:以美国本土两个小流域为例

Analyses of flash-flood response characteristics using long-term rainfall-runoff observational data:a case study of two small watersheds in the United States

以长期降雨-径流观测资料为基础,建立小流域水文单位线以有效描述山洪响应特征,并探究变化环境下的山洪响应特征是否发生改变。单位线在山洪预报中应用广泛,但在气象领域受关注较少。以两个美国小流域(USGS站点02137727-卡托巴河、01572025-斯瓦塔拉河)为研究对象,探讨考虑不同前期降水和致洪降水条件下单位线提取和优化方法,以及前期降水对流域单位线的影响。结果表明不同前期影响雨量下的平均单位线对降水-径流模拟总体效果较好,两个流域1985年以来共16个降雨径流事件模拟的平均纳什模型效率系数分别为0.846和0.940,平均峰值相对误差分别为9.40%和7.47%。前期影响雨量越大,则单位线峰值越高,峰现时间提前。同时考虑前期降水和致洪降水组合的单位线,能更好反映雨洪事件中山洪响应特征,模拟效果进一步提高,对提高山洪概率预报很有意义。通过分析卡托巴河流域33 a单位线的年际变化,发现降水增多和强降水频率增加导致流域山洪响应特征发生明显变化,单位线峰值呈现增加趋势,涨洪历时呈减少趋势,未来山洪灾害风险变大。

This research investigation constructeda unit hydrograph(UH) for the purpose of simulating flash floods in small catchments using long-term rainfall-runoff data.The characteristics of the flash-flood responses were described,particularly from the aspect ofprecipitation.In addition,this study explored how the characteristics of flash-flood responses changed under different environmental conditions.Two small catchments (USGS gauges at the Catawba River and Swatara River) in the United States were investigated in this study.It was found that when the antecedent precipitation indexes (API) were high,the peak UH valueswere higher and the peak current timeshad occurred earlier.The results of the surface runoff simulations using the average UH with different API were considered to be promising,with average Nash efficiency coefficients of 0.846 and 0.940,respectively.The average relative peak errors were determined to be 9.40% and 7.47%,respectively.It was observed that by combining the rainfall and flood-causing precipitation values,the simulation results could be further improved and better represent the characteristics of flash-flood responses.Generally speaking,the method used in this study was considered to have very good potential for real-time flash-flood forecasting processes.Furthermore,further analyses of the interannual variations of UH in the CatawbaRiver Basin indicated intensified flash-flood responses with increasing peak magnitudes and decreasing flood durations.These findingswere found to correspondwell with the increases in both accumulated precipitation amounts and frequency of heavy rainfall observed during the past several years in the study area.