上海市洪涝等级评估及规律分析

Flood grade assessment and law analysis on the historical flood disasters in Shanghai City

城市是社会经济和人类活动的高密集区,极易遭受洪涝灾害损失,城市洪涝评估及规律分析是防洪减灾的基础。目前对于暴雨等级划分已经有相应的阈值标准,但由于城市下垫面条件及排水系统的综合影响,各地区暴雨等级与洪涝等级之间具有一定的地区差异性。以上海市为研究区,选取代表站点1960-2019年历史降雨资料,探究上海市暴雨与洪涝阈值等级关系,选用24 h、48 h以及72 h累积降水量指标,计算不同时间尺度过程降水量经验频率,结合洪涝等级重现期阈值标准,评估上海市不同时间尺度累积降水量指标定量识别洪涝等级,在此基础上利用Morlet小波分析上海市洪涝发生周期性规律。研究结果表明:①上海市50年一遇24 h累积降水量平均为125.3 mm,20年一遇24 h累积降水量平均为99.7 mm,5年一遇24 h累积降水量平均为59.4 mm。②上海市特大或大洪涝平均每2 a就发生一次,中等及以上洪涝平均每年发生2.17次。洪涝发生具有明显的季节性规律,主要发生在夏季和秋季,分别占比65%和28%。③上海市中等及以上洪涝的发生频次并没有明显的周期性规律。本研究为上海市洪涝评估及防灾减灾提供定量化依据。

Cities are highly concentrated areas of socio-economic and human activities and are extremely vulnerable to flood disaster losses.Urban flood disaster assessment and law analysis are the basis of flood management and disaster reduction.At present,there are corresponding threshold standards for the classification of rainstorm levels.However,due to the comprehensive influence of urban underlying surface conditions and drainage systems,there is certain regional differences between rainstorm levels and flood level.Taking Shanghai City as the study area,historical rainstorm data of representative stations from 1960 to 2019 were selected to explore the relationship between rainstorm and flood threshold levels in Shanghai City.Cumulative precipitation indicators of 24h,48h and 72h were selected to calculate the empirical frequency of precipitation in different time scales.Combined with the threshold standard of flood level return period,the quantitative identification of flood based on the precipitation indicators of different time scales in Shanghai was studied.On this basis,the Morlet wavelet was used to analyze the laws of flood and waterlogging in Shanghai to provide quantitative basis for flood assessment and disaster prevention and mitigation in Shanghai.The results of the study show that:(1)the average of 24h accumulated precipitation of Shanghai for return period of 50 years is 125.3mm,the average of 24h accumulated precipitation for return period of 20 years is 99.7mm,and the average of 24h accumulated precipitation for return period of 5 years is59.4mm.(2)In Shanghai,the extremely major or major floods occur once every two years on average,and moderate or above floods occur 2.17 times a year on average.The occurrence of flood has obvious seasonal patterns,mainly in summer and autumn,accounting for 65%and 28%respectively.(3)There is no obvious periodic pattern in the frequency of moderate or above flood in Shanghai.This study provides quantitative basis for flood assessment and disaster prevention and mitigation in Shanghai City.