Author
XU Chunxiao, YUAN Xiaochen, JIN Juliang, LI Jianqiang
Abstract
In this paper, monthly rainfall data at 15 stations in Shaoyang City were used to analyze the characteristics of spatial distribution of regional drought. A drought event is defined as the estimation so as to avoid possible discrepancies. Furthermore, three kinds of Archimedean copulas, i.e., Gumbel-Hougaard copula, Clayton copula, as well as Frank copula, were employed to construct the joint distribution of drought characteristic variables. Then, the copulas’ fitting results were compared, from which the copula of the best fitting results for the estimation of drought return period was selected. Finally, characteristics of the spatial distribution of drought return periods of Shaoyang City in typical drought years were analyzed. Empirical results show that copula theory provides an alternative for multivariable analysis of drought characteristic. The Gumbel-Hougaard copula as well as Frank copula can well reflect the relationships among drought characteristic variables, both of which have similar fitting results. The curve fitting method can avoid the ineffectiveness from estimation of parameters based on data, making the results of copula-based frequency analysis more reliable, with the fitting errors of copulas using the curve fitting method much smaller than those using maximum likelihood estimation. At the Bai mao ping station, the average decreasing amplitude of 3 copulas’ fitting errors employed in this paper reached up to 60.64%. Regional drought has a remarkable characteristic of spatial distribution, resulting in differences in drought extent among stations, e.g., the Dangping station has the highest frequency of drought events, while the Shaodong station shows the least frequency. The maximum drought durations at the Maoping station as well as the Baimaoping station are only 5 months, while become 10 months at the Wugang station. However, the maximum drought severity at the Baimaoping station is only 132.67 mm, which is much smaller than that of 276.24 mm at the Xinning station. In 1963, the severest drought region was in the middle part of Shaoyang City, but the south was severer in 1998. monthly rainfall below the drought thresholds according to the classification of meteorological drought in China, and the drought event is described by two characteristic variables, i.e., drought duration and drought severity. Here, drought duration was fitted with the exponential distribution, while the gamma distribution was used for drought severity. The distribution function of each drought characteristic variable was determined by the curve fitting method instead of maximum likelihood
