Abstract: A diagnostic method of abrupt changes combining sliding window and Copula function is
presented. This method draws dependency diagram in different sliding windows using monthly series of
precipitation and runoff at the Huaxian station of the Wei River, and it fits best Copula functions of
precipitation and runoff based on an Euclidean distance criterion. Results show that in their abrupt change
periods of in 1972 and 1984, precipitation and runoff followed a relationship of T-Copula function in
1951-1972 and 1985-2011 and of Clayton-Copula function in 1973-1984. Advantages of the Copula function
are helpful in simulation of bivariate relationship and deeper understanding of the tail dependence of
precipitation-runoff relationship, which would provide a new approach to variables relationship for random
abrupt changes.