Uncertainty Analysis Of Inconsistent Hydrological Drought Under Changing Environment

This paper takes the Beiluo River Basin as the study area.Based on the measured natural flow sequence of Jiaokouhe Hydrological Station from 1962 to 2016 and Zhangcun Hydrology Station from 1964 to 2016,the consistency of hydrological sequences was first tested to determine the trend of sequence variation and the time of variation.Then the sequence reconstruction method is used to correct the non-uniformity of the hydrological sequence.According to the modified flow sequence,different probability distribution lines are used to fit,and the hydrological drought index(standardized flow index,SFI)is constructed.Perform identification analysis to determine the most appropriate distribution line type.Finally,the SFI uncertainty analysis based on Bootstrap sampling is proposed to quantitatively identify the influencing factors of hydrological drought uncertainty.The following are the main findings and conclusions of this study:(1)The trend test results based on the linear trend correlation test and the Spearman rank correlation test show that the flow sequences of Jiaokouhe and Zhangcun's hydrological stations all show a significant downward trend.The test results of the two test methods are basically the same;using Mann-The kendall method and the Pettitt test identified a mutation in the Jiaokouhe station sequence in 2002,and the Zhangcun station sequence was mutated in 1987.The Mannkendall method can test the trend of the sequence and identify the variability,and the applicability is very strong.(2)In order to eliminate the influence of distribution line type on drought assessment,the gamma distribution,lognormal distribution and normal distribution were respectively fitted to the flow sequence to construct the hydrological drought assessment index SFI.The results show that the gamma distribution and the lognormal distribution fit well,and the three SFIs are compared with the historical drought events by the run-length theory.The SFI calculated by the lognormal distribution is biased in the identification of drought intensity and drought duration.Small difference.Based on the above research conclusions,the SFI calculation uses a gamma distribution to fit the flow sequence.(3)Given the confidence level a=5%,the uncertainty of the distribution parameters,sample size and sampling method on the hydrological drought index is quantitatively described by the confidence interval range.The results show that the larger the sample size is,the smaller the confidence interval is.The percentile Botstrap sampling method has the highest accuracy in estimating the parameter values,which can reduce the uncertainty of hydrological drought assessment.(4)The SFI calculation results of the reconstructed traffic sequence show that the flow sequence based on the variability component can better reflect the flow change trend,and the calculated SFI value is smaller than the restored SFI,and the drought event is identified.A more sensitive and more stable assessment of hydrological drought.