长江中下游地区汛期降水量异常与旱涝趋势

THE ANOMALIES OF PRECIPITATION AND THE DROUGHT/FLOOD TREND DURING RAINY SEASON IN THE MIDDLE AND LOWER REACHES OF THE YANGTZE RIVER VALLEY

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 this paper based on the precipitation data at 48 stations selected evenly over the area to the eastof 100°E and between 25°N and 35°N from 1950 to 1991 and the classified drought/flood data from1470 to1974. the possible anomalies of precipitation and the drought/flood trend duing June-August rainy seasonhave been studied in the middle and lower reaches of the Yangtze River Valley (YRV ). Generally the precipitions are from 450 to 600mm and the relative variabilities range from 0.25 to 0.40 in the rainy season. Thehigh values of the maximum precipitation appeared in the Wuhan area. the common boundary area of Zhejing.Anhui and Jianxi provinces and the Xinghua-Dongtai area of Jiangsu province. The low values of theminmum precipitations were in the Hefei-Huoshan area of Auhui province.Based on the statistical inductive inference. the high values of the possible above-normal precipitaionsoccurred once in 20, 30 and 50 years in the Wuhan and Xinghua-Dongtai areas and Quxian area of Zhejingprovince. whereas the low values of the possible below-normal precipitations occurred once in 20. 30 and 50years in the Dabieshan mountain and the YRVtriangle areas; the possibilities of continued or altrnate occurrence of widespread drought/flood are very small. In the flood/drought data the periods of 50 and 20 yearsand the periods of 100 and 20years are statistically signiricant acroos the middle and lower reaches of theYRVrespectively. It is expected that the droughts could have occur more frequently in the first two decades ofnext century and the flood could have more chance in the first--third decades of next centuty across themiddle and lower reaches of the YRV respectively.