Spatial And Temporal Characteristics Of Extreme Precipitation Events And Their Stable/Nonstationary Study In The Middle And Lower Reaches Of The Yangtze River

This article uses daily rainfall observation data from 75 stations in the middle and lower reaches of the Yangtze River between 1960 and 2012.Based on 11 extreme precipitation indicators,the trend analysis,moving averages,and the Mann-Kendall test are applied to the middle and lower reaches of the Yangtze River and various sub-areas.The temporal and spatial changes of extreme precipitation events in the basin and the concentration and concentration periods of extreme precipitation were studied.At the same time,based on the GAMLSS model,four common two-parameter extreme distribution Weibull distribution(abbreviated as WEI),Gamma distribution(abbreviated as GA),Gumbel distribution(abbreviated as GU)and Log-Normal distribution(referred to as LOGNO)are selected.The distribution of extreme precipitation was optimally fitted to the distribution,and the annual extreme precipitation in the middle and lower reaches of the Yangtze River was estimated.The following conclusions are drawn:(1)Extreme precipitation shows an increasing trend in most parts of each sub-basin.The northwestern part of the Hanjiang River basin,the eastern part of the middle reaches of the middle reaches,the western part of the Dongting Lake,the north part of the Xiangyang Lake,and the northeastern mainstream of the lower reaches have increased significantly.(2)Extreme precipitation accounts for a large proportion of the total precipitation.This indicates that the form of precipitation tends to agglomerate,and the proportion gradually decreases from northwest to southeast.This indicates that the greater the risk of extreme precipitation to the northwest,the greater the risk of disasters.(3)The concentration and concentration periods of extreme precipitation are mainly manifested in that the Han River basin is highly concentrated in late July,the middle reaches of the main stream area is mainly concentrated in early June,and the Dongting Lake is relatively evenly distributed from late May to late June.Poyang Lake is mainly concentrated in the middle and late June and the mainstream of the lower reaches of the river is highly concentrated in late June.(4)The best fitting distribution of 75 stations in the middle and lower reaches of the Yangtze River mainly includes Log-Normal distribution(72 stations)and Gamma(3).Among them,51 stations did not show non-stationarity characteristics,mainly manifested in the stationary characteristics of mean/variance,13 stations showed nonstationarity of variance,5 stations showed non-stationary characteristics of the mean,2 Sites are characterized by the non-stationary nature of the mean/variance.In other words,there are 24 sites that show obvious non-stationary characteristics.Using the residual analysis method to test the goodness of the model's optimal model,it showed that most regions passed the test of goodness of fit.(5)Most of the annual extreme rainfalls show a steady growth trend.In space,the central point of the middle reaches of the middle reaches of the Yangtze River,the Hanjiang River Basin,and the Poyang Lake Basin are the intersections.The higher the annual occurrence,the higher the extreme value is.The spatial distribution of precipitation tends to be centralized.That is to say,the amount of extreme precipitation once encountered in a 100-year period tends to become smaller than the distribution of extreme precipitation in 50 years,and the precipitation increases.This also confirms that the more extreme cases of precipitation events have become increasingly severe,and the extreme precipitation has become larger and more concentrated.This is also one of the direct causes of natural disasters.