Study on coupling relationship between precipitation, soil moisture, and runoff in complex terrain river basins: A case study of Jianxi River Basin in Min River

Abstract

[Objective] Soil moisture is a key variable affecting the precipitation-runoff process. However, the lack of soil moisture observations in complex terrain regions makes it difficult to clarify its mutual feedback mechanisms with precipitation and runoff, which has become a major bottleneck for improving the understanding of river basin hydrological processes and flood forecasting accuracy. Therefore, revealing the co-evolution patterns of soil moisture, precipitation, and runoff, as well as their regulatory mechanisms on runoff, is of great significance for water resources management under changing environments. [Methods] Based on daily observational data from the flood season(April to September) from 2010 to 2021 in the Jianxi River Basin in the upper reaches of the Min River, multiple method including trend tests, ordered clustering, lagged regression, hierarchical analysis, and model comparison were employed to explore the coupling mechanisms of precipitation, soil moisture, and runoff. [Results] The result showed that:(1) after a synchronous abrupt change in precipitation and runoff in July 2010, both entered a long-term stable stage, while soil moisture remained stable, exhibiting the characteristics of a “hydrological buffer”.(2) A significant scale effect was observed in the relationships among the three elements. At the monthly scale, precipitation dominated runoff, whereas at the daily scale, soil moisture had stronger regulatory capacity, indicating that the dominant factor varied with scale.(3) The regulation of soil moisture on precipitation and runoff was state-dependent, with runoff efficiency under wet conditions being 5 to 6 times higher than under dry conditions, and it exhibited a differentiated lag response pattern.(4) Model comparison verified the above mechanisms. The hybrid model integrating precipitation and runoff memory(AR+XGBoost) showed optimal performance(NSE = 0.876), with the contribution rate of its antecedent runoff memory characteristics reaching 13.3%. [Conclusion] The precipitation-runoff transformation in the Jianxi River Basin is a nonlinear process driven by precipitation, with soil moisture serving as a state variable. Its transformation efficiency depends on the antecedent soil moisture state and its lagged regulatory mode. The findings provide a scientific basis for water resources management and flood forecasting in complex terrain river basins.

Keywords

soil moisture / precipitation-runoff relationship / multi-scale analysis / regulatory mechanism / Jianxi River Basin / lagged response / complex terrain river basin / influencing factors