Spatio-temporal Characteristics Of Extreme Precipitation In The Yangtze River Basin And Its Regional Frequency Analysis

Under the background of climate warming,the frequency and intensity of extreme climate events in most land areas are on the rise.The study on the spatial and temporal variation characteristics and regional frequency of extreme precipitation in the Yangtze river basin can provide reference for disaster prevention and reduction in the basin.Based on the observed daily precipitation during 1965-2014 at 130 meteorological stations of the Yangtze river basin,the slope is estimated and MMK inspection analysis temporal variation trend of precipitation sequence,the multiple time scale characteristics of the precipitation sequence were analyzed by using the EEMD method to study,the regional frequencies and spatio-temporal characteristics of extreme precipitation were analyzed by using the L-moments approach,statistical tests and spatial analysis techniques.The results are as follows.(1)Sen-slope was used to estimate the tilt rate of annual precipitation series and extreme precipitation series in the Yangtze river basin,and the trend significance was test by using MMK.The extreme precipitation sequence shows an upward trend in the northeast part of the basin,but the change trend is not obvious in the upper part of the basin.(2)EEMD was used to decompose to obtain the characteristics of annual precipitation series and extreme precipitation series in the Yangtze river basin.The results show that the oscillation period of the annualprecipitation series in the Yangtze river basin is basically consistent with that of the extreme precipitation series,with the inter-annual oscillation around 2.78 a and 5.5a,and the inter-decadal oscillation around 10 a and31a.(3)The annual maximum 1-,3-,7-and 10-day precipitation sequences of the Yangtze River basin can be divided into seven homogeneous sub-regions by fuzzy c-mean classification together with heterogeneity test.The results of Goodness-of-fit measure showed that the GEV and GNO distributions are the optimal distributions for most of the regional extreme precipitation sequences.(4)The accuracy of the extreme precipitation growth curve and quantile estimates was evaluated by using Monte Carlo simulations with inter-station dependence,and the results showed that the root-mean-square errors(RMSE)were bigger and the 90% error bounds were wider with inter-site dependence than those without inter-site dependence for both the regional growth curve and quantile estimates.(5)The regional growth curves with 90% error bands for each homogeneous region showed that the quantile estimates are reliable enough for return periods of less than 100 years,which indicated that extreme precipitation events are highly probable to occur in the middle and lower Yangtze river basin and Szechwan Basin,and hence higher risk of floods.The spatial patterns of annual extreme daily precipitation withreturn period of 100 years indicated that extreme rainfall increased gradually from the upper reaches to the lower reaches of the Yangtze River,showing higher risks of floods in the middle and lower reaches of the Yangtze River,which was consistent with the regional growth curves.