Analysis of Precipitation Characteristics and Wet–Dry Encounter in Major River Basins of Liaoning Province

To systematically explore the variation characteristics of annual precipitation and the interaction between different river basins in Liaoning Province, this study employed multiple scientific methods including linear trend estimation and wavelet analysis. Prior to investigating the wet-dry encounter relationships between basins, a critical step was taken to determine the optimal marginal distribution function for each individual basin—this function mathematically describes the probability distribution of annual precipitation in a single basin, laying the foundation for subsequent bivariate analysis. Additionally, the Copula function, a powerful tool in multivariate statistics for modeling the dependence structure between two or more random variables (independent of their marginal distributions), was calibrated to capture the correlation between precipitation series of any two basins, which involved classifying precipitation status into "wet," "normal," and "dry" categories for each basin and calculating the probability of synchronous (e.g., both wet or both dry) and asynchronous (e.g., one wet and the other dry) occurrences between pairs of basins. The main conclusions are as follows: Except for the Liao River Basin and the Daxiaoling River Basin, the annual precipitation of other major basins in Liaoning Province shows a decreasing trend, among which the YLJ River Basin and the coastal rivers in eastern Liaoning in the eastern region have the most significant decline, with the rates of -0.545 mm/a and -0.753 mm/a respectively. The annual precipitation of each major basin presents three periodicities, namely 4-5 years, 9-14 years and 30-35 years. The Gamma function is selected as the optimal marginal distribution function for the Liao River Basin, the Daxiaoling River Basin and the coastal rivers in western Liaoning; the GEV (Generalized Extreme Value) function is the optimal one for the Huntai River Basin and the YLJ River Basin; and the Log-normal function is the best fit for the coastal rivers in eastern Liaoning. The wet-dry encounter characteristics of precipitation between any two major basins in Liaoning Province show obvious regional differences. The wet-dry synchronization rate is relatively high in adjacent basins, with the rate reaching 0.72 between the YLJ River Basin and the coastal river basin in eastern Liaoning. In contrast, there is a large asynchrony in precipitation wet-dry conditions between the basins in the eastern region (the YLJ River Basin and the coastal rivers in eastern Liaoning) and those in the western region (the Daxiaoling River Basin). The research results can provide a scientific basis for the construction and planning of the water network in Liaoning Province, and also offer technical support for the three-line water diversion scheme of "Transferring Water from Eastern Liaoning to Western Liaoning."