Characteristics And Hydrological Response Of Extreme Precipitation And Temperature In Hexi Inland River Basin

Based on the daily precipitation and temperature data from 1960 to 2010 at 18 meteorological stations in the Hexi Inland River basin,seven indices are constructed to study the characteristics of extreme climate events over the basin.The seven indices include three extreme precipitation indices(AM1D,AM5 D and TWD)and four extreme temperature indices(AMaxT,Txq90,AMinT and Tnq10);Based on the daily precipitation data of 3 meteorological stations in the upper reaches of the Heihe River basin and the daily runoff data of the Yingluoxia hydrological station,the characteristic variables are selected to construct a two-dimensional joint probability distribution model.The main conclusions are as follows:The methods of climate tendency rate,the five-year moving average and wavelet analysis of Morlet,are used to analyze the features of extreme climate indices for all stations.Results show that,extreme climate indices for 55% stations(10 stations)perform waving increasing trends.3~20 years and 23~28 years periodic characters exist for the extreme climate indices,and the first principal period is about 28 years.Moreover a longer periodic feature over 50 years may be exist.Before probabilistic analysis,Mann-Kendall test and Pettitt test are used for stationary checking in the series of extreme climate indices.And then,the non-stationary series are modified.After that,five theoretical probability distribution models,including GEV,Log-Logistic,Log-Normal,Weibull and Gamma,are employed to fit the modified series.The optimal distribution model is selected by Kolmogorov-Smirnov test.Results indicate that GEV distribution model displays the best performance for three extreme precipitation indices and two extreme temperature indices(AMax T and Txq90);Log-Logistic expresses the best fit for the indices of AMinT and Tnq10.Acorrding to the different return level estimates,it appears a decreasing trend from the upper reaches to the lower reaches for the estimates of three extreme precipitation indices,an increasing trend for the estimates of AMaxT and Txq90,and an increasing trend from the upper to the middle,and a decreasing trend from the middle to the lower reaches for the estimates of AMinT and Tnq10.Besides,the frequency and intensity of extreme precipitation indices perform increasing trends over the five-year return period.Under the conditions of climate warming,the estimates of Txq90 and Tnq10 for more than 70% sations at different return periods are always higher than those under the original climate conditions,which means that the extreme temperature indices in the study area present rising trends with climate warming.Based on Archimedean Copula function,a two dimension joint probability distribution is established between annual maximum five-day precipitation(AM5D)and the annual maximum one-day runoff(AM1R)in the upper reaches of the Heihe River basin.The optimal distribution-GEV is chosen as the marginal distribution function.Through RMSE,AIC and BIC goodness-of-fit test,Frank Copula function is the best model to calculate joint distribution probability and return periods.Results show that the greater the value of two characteristic variables,the greater the joint probability and the smaller the joint exceeding probability.The co-occurrence return period is much greater than the joint return period,while smaller than the single return period,as the identical values of AM5 D and AM1 R are combined;When AM5 D is equal to or greater than a particular value,the condition probability of AM1 R increases with the increasing of AM1 R.Under the different given conditions,the larger AM5 D is,the greater conditional probability and conditional return period of AM1 R are.