| In recent decades,the frequency and intensity of extreme rainfall events have increased,which led to more and worse disasters.Therefore,the study of extreme rainfalls is currently an important subject in the fields of meteorology and hydrology around the world.Hydrological frequency analysis is a common method for extreme rainfalls study.Through frequency analysis of extreme rainfalls,the frequency estimates and their spatial-temporal distributions are obtained,which can provide design standard values for the planning and construction of flood control projects,and a basis for the risk assessment and early warning of rainstorms and floods to take measures to reduce losses.In recent years,progress has been made on the research of frequency analysis in China,but there are still some shortcomings,such as limited accuracy of at-site analysis,unideal fitting effect of a single frequency distribution,and significant bias of parameter estimates obtained from conventional moments,in the common methods of frequency analysis.This paper aims to summarize and improve the frequency analysis method in China,and develop a more comprehensive system of rainfall frequency analysis,which is more applicable and objective,based on regional L-moments method.Taking Fujian as the main study area,and Guangdong and Taiwan as supplementary areas,the application research of this rainfall frequency analysis system has been carried out.The main conclusions are as follows:Firstly,the relatively comprehensive rainfall frequency analysis system includes four steps: data collection and preprocessing,identification of hydro-meteorological homogeneous regions,selection of best-fit frequency distributions,and frequency estimates calculation and spatial-temporal consistency adjustments.Using the annual maximum rainfall series for 1 h,3 h,6 h,12 h,and 24 h from rain gauge stations at Fujian and its surrounding buffer zone,a complete rainfall frequency analysis process was carried out.Fujian and its buffer area were divided into 16,16,16,17 and 15 hydro-meteorological homogeneous regions for 1 h,3 h,6 h,12 h,and 24 h,respectively.The main best-fit distributions for the hydro-meteorological homogeneous regions were generalized extreme value distribution(GEV)and generalized normal distribution(GNO).Through spatial-temporal consistency adjustments,the rainfall frequency estimates which were more reasonable and more consistent with statistical characteristics were obtained.The spatial distributions of rainfall frequency estimates show that the main high-value area,which is the high-risk area of rainstorms,is distributed in the coastal area parallel to the coastline.For short durations,the high-value centers are mainly located in the central-southern to the southern coast.For long durations,the high-value centers are located at Ningde in the northeastern coast and in the middle of the Wuyi Mountain.Based on the comparison of the conventional moments and L-moments method,as well as the at-sites and regional analysis,the reliability and superiority of the regional L-moments frequency analysis were verified by unbiasedness and robustness of parameter estimation,distribution selection,and frequency estimates.Secondly,the regional L-moments frequency analysis method,was also applied to Guangdong and Taiwan.The optimal frequency distributions are also GEV and GNO.The spatial distributions of rainfall frequency estimates are consistent with statistical characteristics of rainfall in these areas.Finally,this paper discussed the application of rainfall frequency estimation results obtained by regional L-moments frequency analysis in flood control design and storm flood disaster prevention and early warning.The rainfall frequency estimates were applied to the step-duration-orographic-intensification-factor(SDOIF)method as a better data sample to estimate the Probable Maximum Precipitation(PMP).And the PMP estimations were improved.A database comprised of rainfall frequency estimates and the frequency curve atlases can query the rainfall frequency estimates and the corresponding confidence intervals,estimate rainfall return period,analyze the historical rainstorm cases,and calibrate the parameters in the rainstorm intensity formula.A high-risk rainstorm area atlas can identify high-risk areas of rainstorms and conduct real-time early warning for risks of rainstorm disasters.The regional L-moments frequency analysis system developed in this paper can provide technical reference for rainfall frequency analysis in various regions.New ideas are provided for applications of the rainfall frequency analysis results in construction of flood control projects,urban flood control planning,and early warning for rainstorm and flood disasters.The rainfall frequency estimation results of Fujian,Guangdong and Taiwan can provide references for hydro-meteorological researches and applications in these areas. |
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