Frequency of water and sand abundance and desiccation encounters in Zhangshui Basin based on Copula functions
To investigate the degree of correlation between runoff and sand transport in Zhangshui Basin,the monthly runoff and monthly sand transport data from 1956 to 2020 at the Bashang Hydrological Station were used as the basis for calculat-ing the trends of runoff and sand transport and the characteristics of abundance and desiccation encounters for many years in the basin by using Pettitt's test method and two-dimensional Copula function.The results show that:(1)the annual runoff in ZhangshuiBasin changed gently without significant trend and sudden change;the annual sand transport showed a significant decreasing trend(α<0.01),and produced a significant sudden change in 1994(P<0.001);(2)the Lognormal distribu-tion was the marginal distribution function of the total runoff sequence;the P-Ⅲ distribution was the distribution function for the total sequence of sand transport as well as the abundance and desiccation of water,the runoff in dry water,and the se-quence of pre-variation and post-variation,sand transport distribution function;Clayton Copula function is the optimal joint distribution function of the sequence before and after the variation;Gumbel Copula function is the optimal joint distribution function of the total sequence,the abundance and the desiccation period sequence;(3)The abundance and desiccation en-counter state presented before and after the water-sand variation is different,and the encounter frequency differs greatly.Hu-man activities are the dominant factors of water-sand abundance and desiccation encounter variation in Zhangshui Basin.
Zhangshui BasinCopula functionsabundance and desiccation encountersjoint distribution
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