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在（25°～35°N．100°～125°E）范围内利用48个测站1950～1991年降水资料和1470～1974年旱涝等级资料对长江中下游地区汛期（6～8）月降水异常和旱涝趋势进行了统计分析和推断，得出：长江中下游地区汛期降水量一般在450～600mm．相对变率为0.25～0．40．历年降水量最大值出现在武汉地区、浙皖赣交界地区以及苏北兴化─东台地区、最小值出现在安徽合肥─霍山地区，20a、30a、50a─遇的异常多降水量的最大值出现在武汉、衢县及兴化─东台地区，异常少降水量的最小值出现在大别山及长江三角洲地区．大范围旱涝连续出现和交替出现的可能性很小，在长江中游地区汛期旱涝具有50a和20a的周期变化，长江下游地区具有100a和20a的周期变化，本世纪80年代以来长江下游地区降水量波动增加．预计下世纪10～30年代将是洪涝多发期．10～20年代长江中游地区将是干旱多发期．
In the range of (25 ° -35 ° N.100 ° -125 ° E), the precipitation data of 48 stations from 1950 to 1991 and the data of drought and flood level from 1470 to 1974 were used to analyze the flood season (June to August) in the middle and lower reaches of the Yangtze River Precipitation anomalies and droughts and floods were analyzed and inferred. The results show that precipitation in flood season in the middle and lower reaches of the Yangtze River is generally in the range of 450-600 mm. The relative rate of change is 0.25 ~ 0.40. The maximum precipitation over the years occurred in Wuhan, the junction of Zhejiang, Anhui and Jiangxi provinces and Xinghua - Dongtai area, the minimum occurred in Hefei-Huoshan area of Anhui, 20a, 30a, 50a-the maximum number of anomalies encountered in Wuhan , Quxian and Xinghua-Dongtai areas, the minimum of anomalous and less precipitation occurred in the Dabie Mountains and the Yangtze River Delta. There is a small possibility of continuous emergence and alternation of large-scale droughts and floods. The flood and drought in the middle reaches of the Yangtze River have periods of 50a and 20a, and the lower reaches of the Yangtze River have periods of 100a and 20a. Since the 1980s, the precipitation in the lower reaches of the Yangtze River Fluctuation increased. It is estimated that 10 to 30 years of the next century will be flood prone periods. The mid-Yangtze River in the 10 ~ 20 years will be a drought period.