2020年淮河上游暴雨对王家坝水位影响预估分析

Analysis of the Impact Estimation of Heavy Rainfall in the Upper Reaches of Huaihe River on the Water Level of Wangjiaba Flood Barrier in 2020

王家坝闸是淮河防洪的第一道屏障,淮河上游(河南省中东部、东南部)出现的暴雨及相应的面雨量是导致王家坝水位变化的直接因素。流域面雨量的监测预报是洪水预报与调度的重要参数,也是各级政府指挥防汛抗洪的决策依据。2020年汛期由于河南省淮河上游出现持续性洪水,致使7月20日王家坝开闸泄洪,这是继2007年开闸泄洪13年后的又一次开闸泄洪。为了进一步发现淮河致洪的降水特征、面雨量特征及预报关注点,提升淮河防汛抗洪能力,对2020年导致王家坝水位演变的淮河上游降水特征、分区面雨量特征及历史上淮河致洪相似年大尺度环境条件进行了分析。结果表明:(1)2020年汛期淮河上游降水与王家坝的水位演变密切相关,主要分为3个阶段,即旱涝急转阶段,王家坝水位缓慢升高再回落徘徊期;连续性暴雨阶段,王家坝水位接近警戒水位期;大暴雨阶段,王家坝开闸泄洪期。(2)淮河干流片连续5天累积面雨量≥100 mm时,可导致王家坝水位迅速升高,出现超警戒水位洪水;汝河片单日面雨量≥50 mm,且王家坝接近超警戒水位时,未来6天王家坝水位缓慢上升或基本维持。(3)研发的“淮河上游面雨量预报及王家坝水位涨幅预估系统”,经2020年汛期应用,预报误差小,有较好参考价值,特别是结合智能网格降水预报结果,预估7月1718日淮河干流片面雨量≥50 mm,将致王家坝水位上涨4.6~5.4 m,出现超警戒或超保证水位风险极高,与实况基本吻合。(4)以淮河上游致洪暴雨集中期为相似确定2007和2020年互为最相似年份,归纳出王家坝出现超警戒水位的暴雨预估指标、淮河致洪暴雨产生的环流特征和环境条件,为淮河上游致洪暴雨决策服务提供科学依据和技术支撑。(5)暴雨频发、降水落区重叠、降水中心强度大且降水具有连续性是导致2020年淮河王家坝开闸泄洪的重要原因。淮河干流片面雨量对王家坝水位增长起决定作用。

Wangjiaba Flood Barrier(WFB)is the first barrier of flood control in Huaihe River.The heavy rainfall and corresponding areal rainfall in the upper reaches of Huaihe River(east-central and southeastern part of Henan Province)are the direct factors leading to the variation of water level in WFB.The monitoring data and forecasts of rainfall in the basin are important parameters for flood forecasts and water level adjustment,and are also the bases for the decision-making for governments at all levels to command flood control.During the 2020 flood season,WFB was opened for flood release on July 19 because of persistent flooding.It has been 13 years since the last opening in 2007.In order to further investigate the characteristics of precipitation and areal rainfall as well as the forecast concerns of the Huaihe River flooding,and to improve the flood control and anti-flooding capability of the Huaihe River,this paper analyzes the factors responsible for the evolution of the WFB water level,including the precipitation characteristics of the upper reaches of the Huaihe River,the areal rainfall characteristics in 2020 and the large-scale synoptic conditions of the Huaihe River flooding in historical similar years.The results show that:(1)the precipitation in the upper reaches of the Huai River was closely related to the variation of the WFB water level in the main stream of the Huaihe River during the 2020 flood season.The changes of the WFB water level are divided into three stages,i.e.,from sudden turn of drought and flood to the period when the water level of WFB slowly rose and then fell back;from continuous heavy rainfall to the period when the water level of WFB rose close to the warning level;and from heavy rainfall to the period when the water level of WFB exceeded the guaranteed level and the water level of the basin reservoir exceeded the flood limit.(2)Accumulated areal rainfall≥100 mm in five consecutive days over Huaihe River main stream caused the water level of WFB to rise rapidly and flooding above warning level.When the daily areal rainfall is≥50 mm over Ruhe area and the water level of WFB is close to the over-warning level,the water level of WFB slowly tends to rise in the next six days or basically maintains the high water level.(3)The scientific research result of Huaihe River basin flooding rainfall,i.e.,the areal rainfall forecasting over the upper reaches of Huaihe River and the water level of WFB prediction system,was applied during the 2020 flood season,showing small forecast errors.So,it is a good reference for forecasters.Especially combined with the results of the intelligent grid precipitation forecast,the Huaihe River main stream areal rainfall≥50 mm in July 1718 was predicted,which would cause the water level of WFB to rise by 4.65.4 m,with a very high risk of over-alert and over-guaranteed water level.The forecasts and the observations basically match.(4)The flooding rainfall concentration period in the upper reaches of the Huai River in 2020 was similar to that in 2007.So,the forecast indicators,the circulation characteristics and environmental conditions of the rainstorm which led to exceeding the warning water level in WFB are summarized.It provides scientific basis and technical support for the decision-making service of the Huaihe River upstream flood rainstorm.Therefore,the frequency of heavy rains,overlapping precipitation areas,and high intensity of precipitation centers and continuous precipitation are important reasons for the opening of WFB in the Huai River in 2020.The bigger amount of rainfall on the main stream of Huaihe River plays a decisive role in the growth of water level in WFB.The areal rainfall forecasting over the upper reaches of Huaihe River and the water level of WFB prediction system provides decision-making basis and technical support for the Huaihe River flood control and disaster reduction in 2020.