2020年8月黄河中游致洪暴雨气象水文特征

利用ECMWF提供的ERA5再分析资料(分辨率0.25°×0.25°)和黄河流域加密的气象水文实况资料,分析了降水集中期的气象水文特征。结果表明:平均中纬度低槽、南亚高压和阻塞高压偏强,副热带高压位置偏西、偏北,且异常偏强是造成2020年8月黄河中游持续性强降水的主要环流背景;水汽输送较常年同期偏多,来自东海和孟加拉湾的东南和西南暖湿气流沿副热带高压边缘不断输送到黄河中游地区,并和中纬度低槽携带的冷空气在此交汇形成持续性的强降水。水文特征分析表明,导致潼关水文站出现3次洪水的较大面雨量,主要来源于潼关以上的8个子流域;2020年8月的洪水超过2011年9月的,为潼关站近20 a来的最大的洪水过程;5号和6号洪水连续超过编号标准的时长,为120 h和44 h,最大流量达6 300 m³·s^-1;流量开始增加的时间落后降水开始的时间12 h~3 d,峰值落后降水结束的时间12 h~4 d;黄河支流水文站的流量峰值与水文站所在子流域降水范围、量级呈正相关,流入潼关站的流量从大到小依次为龙门站、华县站、状头站和河津站。历史对比表明,2020年8月黄河中游累积面雨量为近30 a来最大,北部6个子流域面雨量表现更为极端,降水持续时间更长。

Meteorological and hydrological characteristics of flood causing rainstorm in the middle reaches of the Yellow River in August 2020

Based on the ERA5 0.25°×0.25° reanalysis data provided by ECMWF and the encrypted real meteorological and hydrological data of the Yellow River Basin, the meteorological and hydrological characteristics of the precipitation concentration period were analyzed. Results show that the average mid-latitude low trough, South Asian High and blocking high are strong, and the subtropical high is located west to north and abnormally strong. These are the main circulation background that led to the persistent heavy precipitation in the middle reaches of the Yellow River in August 2020. The water vapor transportation is abnormally more than the same period of the previous year. The southeast and southwest warm and humid air flow from the East China Sea and the Bay of Bengal is continuously transported along the edge of the subtropical high to the middle reaches of the Yellow River, where it intersects with the cold air carried by the mid-latitude low trough to form continuous heavy rainfall. The analysis of hydrological characteristics shows that the large areal rainfall that led to the occurrence of three numbered floods at the Tongguan Hydrological Station mainly came from the eight sub-basins above Tongguan. The flood in August 2020 exceeded that in September 2011, and was the largest flood in Tongguan Station in the past 20 years; The duration of No.5 and No.6 flood were 120 h and 44 h longer than numbering flood standard, with a maximum flow of 6 300 m³·s^-1. The time when the flow began to increase is 12 h-3 d later than the time of precipitation starts, and the peak is 12 h-4 d later than the time of precipitation ends. There is a positive correlation between the peak discharge value of hydrology station of Yellow River tributaries and the range and magnitude of precipitation in the sub-basin where the hydrology station is located. The flow into Tongguan station is Longmen station, Huaxian station, Zhuangtou station and Hejin station in descending order. Historical comparison shows that the accumulated areal rainfall in the middle Reaches of the Yellow River in August 2020 is the largest in the past 30 years, and the areal rainfall in the six sub-basins in the north of the Yellow River was more extreme and the rainfall duration was longer.