Identification of abrupt changes of the relationship between rainfall and runoff in the Wei River Basin, China

The relationship between rainfall and runoff in the Wei River Basin, one of the most important relationships in hydrology, possibly changed due to the changing climate and increasingly intensifying human activities. The identification of abrupt changes of the relationship will help to further understand the changing mechanism of runoff generation, being a great stimulus to the development of water resources planning and management. Therefore, a new method based on copulas was employed to detect change points of the relationship. Additionally, a Bayesian copula selection method was employed to choose the most appropriate copula, and the primary conclusions are as follows:(1) the Bayesian copula selection method based on Bayesian analysis is independent of parameter selections and easy to implement; (2) the identified change points can be summarized as the early 1970s, the late 1980s, and the middle 1990s; (3) from climate change perspective, the combined impact of increasing air temperature and initially decreasing then increasing potential evaporation had a certain effect on these change points; from human activities perspective, the underlying causes of these change points of the early 1970s, the late 1980s, and the middle 1990s were the construction of water projects and soil conservation, the growing effective arable land of the late 1980s and the growing utilization of water resources in the middle 1990s, respectively. The dominant factor influencing the relation between precipitation and runoff is the increasingly intensifying human activities, and this relation is increasingly weakening.