Temporal and Spatial Variation Characteristics of Base Flow and Its Influencing Factors in Middle and Lower Reaches of Yangtze River

Base flow is an important part of runoff, so it is important to choose a reasonable base flow segmentation method to estimate base flow, understand the changing characteristics of base flow and base flow index, and identify the driving factors of base flow and base flow index change for the protection and management of river ecology. Based on the daily runoff data and meteorological data of 64 hydrological stations in the middle and lower reaches of the Yangtze River, the base flow segmentation results of three digital filtering methods (Lyne-Hollick method, Chapman-Maxwell method, and Eckhardt Method) and smoothing minimum method were compared, and the driving factors of base flow and base flow index changes were analyzed from the aspects of climate and underlying surface factors. The results show that the Chapman-Maxwell filtering method is more suitable for base flow segmentation in the middle and lower reaches of the Yangtze River. The base flow of the main stream in the middle and lower reaches of the Yangtze River is much larger than that of tributaries. The base flow is greater in wet seasons than in dry seasons, while the base flow index is not significantly different between the main stream and tributaries, and the base flow index is significantly greater in dry seasons than in wet seasons. Climate and underlying surface are the driving factors of base flow changes between wet and dry seasons. Specifically, climate is the dominant factor in the reduction of base flow in wet and dry seasons, while the underlying surface is the dominant factor in the increase of base flow in dry seasons.