Alteration of inner-annual runoff distribution and attribution analysis of Longchuan station at Dongjiang River

Due to the climate change, human activities and other factors, there are some inter-annual or inner-annual alterations happened in the hydrological series. Many important works had been affected severely, such as the planning and designation of hydraulic engineering, the sustainable utilization and optimal allocation of water resources etc. However, the studies about the features of inner-annual hydrologic elements distribution are mainly focused on the analysis of the inhomogeneity, with the disadvantage of unintuition and the poor comparability of the indicators from the view of methods that used nowadays, few of the studies considering the alteration of the inhomogeneity happened or not under the changing environment. Therefore, the Gini Coefficient with the advantage of well description of inhomogeneity is used to set up the analysis method of hydrological alteration of the inner-annual distribution. In this method, the series of homogeneity of inner-annual hydrological elements distribution will be calculated first of all, then the Hydrological Alteration Diagnosis System is used to analyze whether the alteration is happened in the series or not, finally, the mean difference method will be employed to analyze the attributions if the alteration is existing. At the end of this study, with the monthly runoff data from the year of 1954 to 2005 of Longchuan Station at Dongjiang River, the alterational characteristics of inner-annual runoff distribution is calculated and the attribution analysis is conducted in succession. The results show that: at the year of 1973, the increasing jump alteration happened in the series of inner-annual runoff distribution, which means the tendency of inner-annual runoff distribution becomes equalization. About 60% of the alteration is induced by the human activities, especially the construction and operation of Fengshuba Reservoir, and the factor of climate change only accounts for about 40%.