In order to explore the root causes for the decline of Yongding River natural runoff since the 1980s

this article diagnoses the change points in the natural runoff series at typical hydrological stations in the Yongding River Basin

uses Copula function to study the variation characteristics of the natural runoff and precipitation-runoff response structure relationship in the Yongding River Basin

and discusses the main causes of these variations. The study shows that from 1956 to2016

the natural runoff series in the main and tributary streams of the Yongding River exhibited significant trends of attenuation and abrupt changes. The marginal distribution

joint distribution

and conditional distribution probabilities of the correlation structure between precipitation and runoff showed significant adjustments before and after 1983. The joint probability and distribution interval of precipitation and natural runoff decreased significantly during the change period

and the amount of precipitation that meets the same runoff needs increased significantly during the change period

indicating that the hydrological response relationship and runoff mechanism in the Yongding River Basin have undergone fundamental changes since the 1980s. The conversion of farmland to forests

urbanization

and groundwater exploitation might be the reasons for the variation in the natural runoff and hydrological response relationship of Yongding River.