Hydrological Drought Index And Drought Frequency Calculation Methods

Drought is a global issue, including meteorological drought, agricultural drought, hydrological drought and socio-economic drought. Hydrological drought is in close relationship with hydrological cycle and water balance, but is less concerned in reality. Hydrological drought is the ultimate manifestation of various types of drought, and it is a continuation of meteorological and agricultural drought, which means serious water resource shortage.Proceed to the runoff distribution characteristics as a starting point, through the eigenvalues distribution curve to understand the characteristics of runoff during annual and interannual variability, the results show that:Fenhe River upstream runoff distribution in one year is relatively even, but annual runoff distribution is uneven; there are four significant dry seasons and three consecutive significant continuous wet periods. Analyzing runoff characteristics of a single and continuous high and low flow based on set pair analysis, conditional probability and Markov Process.It shows that probability of low streamflow is38%, it most prone to continuous low flow upstream, followed by normal flow and ended by high flow. To fully understand the hydrology characteristics of the study area both pave the way for the hydrological drought research, but also have a preliminary understanding to drought.Basic hydrological research is to establish drought assessment index, similar to the process of establishing meteorological drought index. In view of skewed probability distribution, Standardized Runoff Index is counted. Regression and hypothesis testing are used to determine significant linear correlation between Standardized Precipitation Index and Standardized Runoff Index. To classify the level of drought, correlation coefficient is used to revise Standardized Runoff Index. It shows that hydrological drought index derived from runoff data is reasonable and effective, and watershed characteristics are discovered in the comprehensive correction factor of Standardized Runoff Index.The goal is to calculate the probability distribution of drought characteristic variables and return period. Copula function is used in drought frequency analysis. Firstly drought sequence based on run theory is extracted, and then the union probability distribution models of drought characteristic variables are constructed in Fenhe River upstream dimensional Archimedean Copula function. Finally, optimal Copula function is selected based on criteria of minimum ordinary least square, Akaike information criterion and Bayesian Information Criterions. After calculating parameters, union distribution of drought duration and drought intensity and union return period are derived.