Analysis Of Drought Characteristics And Drought-resistant Ability Of The Yellow River

With the increasing demand of water resources and the change of global climate,drought has become the most serious natural disaster in our country.Drought is one of the most frequent natural disasters in the Yellow River basin,which has a serious impact on the local people's life and social economic development.It is of great significance to understand the regularity of drought in the Yellow River basin in order to effectively identify drought and prevent drought.Water conservancy projects have played an important role in flood control,irrigation,power generation and water supply.In this paper,drought characteristics and drought-resistant ability of the yellow river are studied.According to the characteristics of climate and geographical location of the Yellow River basin,106 weather station meteorological data,the water station runoff data of the the Yellow River basin from1960 to 2013 are used.The main research content and results of this paper are summarized as follows:(1)The drought indexes are calculated by meteorological and hydrological data of the Yellow River basin and reservoir.Each region's drought indexes are calculated include meteorological drought index(standardized runoff index,standard evapotranspiration index),hydrological drought index(normalized flow index),agricultural drought index(Palmer drought index and drought index)and the modified surface hydrology supply index.Various types of the Yellow River river basin the drought was serious,the most serious drought is hydrological drought.The meteorological drought in the upper reaches of the Yellow River is serious.Hydrological drought and agricultural drought is serious in the middle and lower reaches of the Yellow River.There is a tendency of drought in the whole basin.(2)The principal component analysis(PCA)method is used to calculate the principal component contribution rate and characteristic vector of each partition in the the Yellow River River basin.Compared with the actual drought events,it is proved that this index can reflect the drought situation of the Yellow River basin.The frequency of light drought occurred in all regions below Hua Yuankou is higher than it in ot her regions.In 1990 s,the drought in the Yellow River is significantly more severe than other previous years.By using wavelet analysis,the drought cycle in the Yellow River basin is about 5 years.From the upper reaches of the the Yellow River River to the lower reaches of the Yellow River,the main drought period turns to be smaller.The main source area period is about 27 years.The main cycle of the middle reaches is about 20 years,Drought period of the lower reaches is only 5 years.Indicating that drought alternation is more and more frequent.(3)Using the beta distribution,Gamma distribution,normal distribution and exponential distribution to simulate the drought duration and drought intensity in the lower reaches of the Yellow River River basin.Three Copula functions are used to fit the distribution function of drought duration and intensity in the lower reaches of the Yellow River river include Gumbel Archimedes? Clayton Copulas?Copula Copulas and Frank Copulas.And the root mean square error method(RSME)is used to determine the optimal fitting function.After calculation,the distribution of drought in the lower reaches of the Yellow River is determined by exponential distribution function and the Gamma distribution function is used to calculate the drought intensity.The optimal Clayton Copulas function is chosen as the connection function of the drought duration function and the drought intensity function in the lower reaches of the Yellow River River basin.(4)The drought recurrence period in the lower reaches of the Yellow River River Basin is obtained according to the duration of drought?drought intensity and the probability of joint distribution of Copula combined with the expectation of drought interval.Through the evaluation of the different drought patterns,we can see that the lower reaches of the the Yellow River River Basin are short duration light drought and moderate drought,and the occurrence frequency is much higher than that of the strong drought intensity.The recurrence period increases gradually with the increase of drought duration and intensity.Generally speaking the drought is serious in the lower reaches of the basin and the proportion of moderate and severe drought patterns is greater than 50% in all degrees of drought.(5)Based on the nature of drought and the formation mechanism of drought disaster,this paper puts forward the calculation principle and method of drought response ability of reservoir group.Taking the lower reaches of the Yellow River as an example,this paper calculates the capacity of reservoir based on the genetic algorithm.The study shows that the lower reaches of the Yellow River average water shortage rate is higher(10.96%).The reservoirs in the lower reaches of the Yellow River River Basin has ability to cope with the drought which return period is 20a~25a drought.Drought resistance index is 0.8904.When the return period of drought is less than 40 a,the reservoirs in the Yellow River downstream is likely to control serious drought and can make it to be moderate or mild.The drought-resistant ability level is weak in the lower reaches of the Yellow River when drought recurrence period is 25~60 years or 60~100 years.For the drought happens 100~200 years once the drought-resistant level is very weak.(6)This paper constructs the evaluation index system of Drought Adaptability in the Yellow River basin.It bases on the influence factors of water conservancy project and the river basin's own project scale and operation management.Using the analytic hierarchy process(AHP)and entropy weight method to evaluate the adaptability of drought in the Yellow River River Basin by using the variable fuzzy method.The drought grade value in the middle reaches of the Yellow River is lower than that of the upper and lower reaches.At present,the Yellow River river basin water conservancy project construction status quo is consistent with each basin regional drought characteristics.Layout planning of water conservancy projects in the Yellow River remains to be perfect in order to improve the regional drought coping ability.