Analysis of Runoff Distribution Characteristics and Evolution Patterns of Pingtan and Minjiang River Estuary Water Resource Allocation

The analysis of runoff distribution characteristics and evolution patterns of the Pingtan and Minjiang River Estuary Water Resource Allocation (‘One Gate- Three Lines’) Project holds significant importance for optimizing the spatial equilibrium allocation of water resources in Fujian province. Based on long-term runoff data series spanning over six decades from five major water sources along the project, including representative stations such as Yongtai Station and Zhuqi Station, this study employs Mann-Kendall rank correlation method, Pettitt change-point detection, wavelet analysis, concentration degree (CD) and concentration period (CP) to systematically characterize interannual and intra-annual allocation patterns in water source areas. Besides, using Copula function to analyze the wetness-dryness encounter characteristics between water sources. The results show that: In terms of interannual variations, the runoff at Yongtai Station exhibited a significant decreasing trend throughout an entire year and during flood season, undergoing a significant abrupt change in 2000; whereas the runoff at Zhuqi Station during non-flood season showed a significant increasing trend, with its abrupt change point identified in 1981. Wavelet analysis revealed dominant periodicities of 8~18 years for both annual and flood-season runoff across all water sources, while non-flood-season runoff exhibited primary cycles spanning 5~13 years. Regarding intra-annual distribution, runoffs at stations are concentrated during May to September, with concentration degree (CD) values ranging from 0.40 to 0.53, indicating relatively uneven distribution. Notably, runoff concentration may decrease at Yongtai and Zhuqi Stations, while the concentration period (CP) shows a potential delaying trend in projected future runoff. Regarding wet-dry encounter characteristics, significant hydrological compensation patterns are observed among runoff of different water sources, which provide favorable conditions for implementing multi-source joint operations, with synchronous occurrence probabilities of wetness-dryness conditions ranging from 0.47 to 0.65 and asynchronous probabilities spanning 0.35 to 0.53. The multi-scale analytical framework developed in this study for spatiotemporal runoff variations provides a scientific foundation for formulating coordinated multi-source operation strategies in trans-basin water transfer projects.