2021年汉江秋汛的水雨情及环流异常特征研究

Study on Hydrological and Rainfall Characteristics and Circulation Anomalies in Autumn Flood Season of Hanjiang River in 2021

利用NCEP/NCAR再分析资料及常规气象水文实况观测资料,研究2021年汉江秋汛的水雨情及环流异常特征,并初步分析致洪成因,结果表明:2021年汉江流域降水呈“西多东少”分布,汉江上游累计降水量为400~985 mm,累计面雨量居1961年以来第一位。秋汛期间丹江口水库出现10000 m^(3)·s^(-1)以上的洪峰过程7次,汉江中下游主要水文控制站点累计超警时间为151~580 h,最大超警幅度为0.29~1.56 m,呈现越到下游超警时间越长、超警幅度越大的特征。与2011年和2017年水情对比表明,2021年汉江上游洪峰出现时间最早,洪峰次数最多,上游高水位流量持续时间最长,汉江中下游累计超警时间也最长,水情异常程度明显更强。在大气环流形势方面,巴尔喀什湖—贝加尔湖地区为负异常,我国大陆东部至西北太平洋为正异常,日本岛以东地区为负异常,副热带高压、南亚高压、东亚副热带西风急流较历史同期偏强,异常的低层流场及水汽辐合中心的形成,以及对流层高层的辐散抽吸,是汉江上游降水得以持续并阶段性增强的有利环流配置。当丹江口水库入库流量接近2000 m^(3)·s^(-1)后,汉江上游超过60 mm的5 d累计面雨量与10000 m^(3)·s^(-1)以上洪峰的出现密切相关。上游来水增大后,汉江中下游河道逐级收窄是导致此地降水并不明显却出现超警洪水的主要原因。

Based on NCEP/NCAR reanalysis data and conventional meteorological and hydrological observation data,the meteorological and hydrological characteristics as well as circulation anomalies and possible causes of the autumn floods in Hanjiang River in 2021 are analyzed.The results show that the precipi-tation in Hanjiang River in 2021 was more in the west and less in the east.The accumulated rainfall in the upper reaches of Hanjiang River was 400-985 mm,and the accumulated areal rainfall ranked the first since 1961.During the autumn flood season,the Danjiangkou Reservoir experienced the flood peak processes of more than 10000 m^(3)·s^(-1) for 7 times.The accumulated alarm time of the major hydrological control stations in the middle and lower reaches of the Hanjiang River got to 151-580 h,with the maximum amplitude beyond warning line being 0.29-1.56 m,showing the characteristics of the longer alarm time,the higher amplitude over warnig line in the lower reaches.The comparison with the hydrological conditions in 2011 and 2017 shows that in 2021 the flood peak in the upper reaches of Hanjiang River came the earliest,the number of flood peaks was the largest,the duration of high water level in the upper reaches was the longest,the accumulated alarm time in the middle and lower reaches of Hanjiang River was also the longest,and the abnormal degree of water regime was significantly much stronger.In terms of atmospheric circulation,the low trough of Lake Balkhash and Lake Baikal region,the high ridge from the east of China's Mainland to the Northwest Pacific,the low trough in the areas to the east of Japan Island,the subtropical high,the South Asian high and the East Asia subtropical westerly jet were all abnormally stronger than those in the same period in history.The formations of abnormal low-level flow field and water vapor convergence center,combined with the divergence and suction of high-level flow field,were the large-scale circulation background favorable for the continuous and enhancement of precipitation.When the inflow of Danjiangkou Reservoir was close to 2000 m^(3)·s^(-1),the 5 d accumulated areal rainfall exceeding 60 mm in the upper reaches of Hanjiang River was closely related to the appearance of flood peaks above 10000 m^(3)·s^(-1).After the upstream inflow increased,the narrowing river coarse of the middle and lower reaches of the Hanjiang River was the main reason for the over-alarm-line floods in this area where the precipitation was not so heavy.