Quantitative Analysis Of Regional Drought Hazard Based On Cloud Model Theory

Drought is a serious natural disaster in the world today.It has the characteristics of high frequency,long duration and wide range of impact.In the quantitative analysis of regional drought risk,selecting the appropriate drought index and drought frequency analysis are two key points.The drought index is the basis of drought research,and the construction of a universal comprehensive drought index is an important work at present and an important basis for drought monitoring and drought risk assessment.A single factor drought index is proposed for each type of drought.At present,the commonly used drought indexes at home and abroad include standardized precipitation index(SPI),standardized runoff index(SRI),precipitation anomaly percentage(Pa),standardized soil moisture index(SSI).However,most of the single-factor drought index can only reflect the impact of one factor on the drought,but it cannot fully reflect the characteristics of the regional drought affected by multiple factors.To this end,the uncertainty reasoning method based on the cloud model is used to integrate the two indices of precipitation anomaly(Pa)and soil moisture anomaly(SMAPI)to construct an index that can simultaneously recognize the characteristics of the above two indexes.The drought index DI is integrated and used in the identification and analysis of drought characteristics in Anhui Province from 1960 to 2007.The Pearson III(P-III)type curve and graphic method specified in the "Code for Design Floods of Water Conservancy and Hydropower Projects" in China is a commonly used method to derive the hydrological value of the specified frequency.The formula is determined,but the formula has certain drawbacks,and there is a long-term controversy and confusion about the choice of the correct experience frequency formula.Precipitation is an important way to replenish and renew water resources.The lack of precipitation is the main cause of meteorological drought.Especially for dry and semi-arid areas with low rainfall,the frequency analysis of related drought indices such as precipitation is very important.This paper presents a new empirical frequency calculation method based on cloud transformation,analyzes the annual precipitation series of 5 observation stations in northern Anhui to complete the verification of the rationality of this method,and on this basis,based on the comprehensive drought index Analysis of drought frequency in northern Anhui.The above research results show that:(1)The comprehensive drought index DI combines the common advantages of meteorological drought and agricultural drought index in the identification of drought process,and has good accuracy and applicability;(2)The annual drought in Anhui Province is mainly light and moderate drought.Seasonal droughts have frequent droughts in autumn and high grades,and have a wide range of disasters,followed by winter,heavy and extremely drought in spring,and the weakest summer;(3)There are relatively more light droughts in the central and southern regions of Anhui Province,and relatively more moderate,severe,and extreme droughts in the northern region.The drought risk gradually increases from south to north.The center of gravity of the drought moved from the central part to the northwest from the 1960 s to the 1990 s,and shifted to the south from 2000 to 2007,forming a circular counterclockwise route;(4)The Mann-Kendall trend non-linear test method was used to analyze the Anhui Province comprehensive drought index DI series trend,and the annual scale test value Z was-0.0756,showing a downward trend,with an upward trend in spring and autumn and a downward trend in summer and winter;The northern part of Anhui Province showed an upward trend,while most of the central and southern regions showed a downward trend;The first main cycle of the change of DI in Anhui Province is 25 a,and the first main cycle of four seasons of drought index is 6a,32 a,20a,7a;(5)Aiming at the annual precipitation sequence of 5 stations in the northern Anhui area,the new frequency of cloud transformation can be used to obtain the precipitation value of the design frequency,and the result is close to the precipitation value obtained by using the original expectation formula.The design value obtained at one of the stations is slightly larger than the latter,and the rest are less than the design frequency precipitation value obtained by the original expected formula;(6)Based on the comprehensive drought index,the drought frequency in northern Anhui was analyzed,and the occurrence probability of drought intensity at different levels in various cities was obtained.The results are partially different from the probability values obtained through drought frequency statistics,but the overall consistency is consistent.Drought risk index shows a gradual increasing trend from south to north.