Using Copula Model to Analyze Consecutive Wetting-drying Occurrence in Rainfall-runoff in Hanjiang Basin

Abstract

【Objective】 Hanjiang is the largest tributary of the Yangtze River. The purpose of this paper is to analyze the consecutive occurrence of wetting-drying in rainfall and runoff in order to improve water resource management in this basin. 【Method】 The analysis was based on runoff data measured from four hydrological stations and precipitation measured from a control catchment in the basin. The joint distribution of wetting-drying for rainfall and runoff was constructed using the two- and three-dimensional Copula functions. The risk probabilities of occurrence of wetting-drying for rainfall and runoff were calculated. 【Result】 The probability of consecutive occurrence of wetting and drying between runoff and rainfall at Shiquan and Baihe stations in the upper reaches in the basin were higher, being 73.06% and 73.45% respectively. The probability of consecutive occurence of wetting and drying at Huangjiagang station in the middle reaches of basins was the highest, reaching 45.21%. The probabilities of consecutive occurrence of wetting and drying at Shiquan, Baihe and Huangjiagang stations in the upper and middle reaches of basin was ranked in the order of dryness > synchronous wetness > synchronous normal, while at Xiantao station in the lower reaches, the synchronous wetness-dryness probability showed the synchronous normal > synchronous dryness > synchronous wetness. The synchronous wetness-dryness probabilities of rainfall in the control catchment for the combination of Shiquan, Baihe and Huangjiagang stations in the upper and middle reaches of the HRB were higher, 72.88%; the synchronous wetness-dryness probabilities of rainfall in the control catchment under different combinations of stations showed the synchronous normal > synchronous dryness > synchronous wetness, and that of runoff showed the synchronous dryness > synchronous wetness > synchronous normal. 【Conclusion】 The consistency of wetness and dryness for runoff and rainfall in the upper and lower reaches of the basin was good and fairly good, and is poor in the middle reaches. The wetness-dryness of rainfall in the control catchment under different stations has relatively good consistency, while the difference between the synchronous and asynchronous wetness-dryness probabilities of runoff was not significant.

Keywords

• hanjiang river basin
• copula function
• rainfall and runoff
• wetness-dryness encountering
• risk probability