Unraveling the Responses of Rainfall-runoff Event Characteristics and Runoff Processes to Land Use Change: A Case Study of Upper Fenhe River in China

Land use change profoundly influences the hydrological processes, especially in semi-arid and semi-humid regions, subsequently altering the runoff characteristics. However, the quantitative relationship between land use and runoff processes remains unclear. This study investigated temporal variations in rainfall-runoff characteristics at the event scale by analyzing 85 flood events in the Jingle watershed of the upper Fenhe River, China. The spatial variation in the dominant runoff processes across different land use was quantified using a Geographic Information System (GIS). The results indicated a significant shift in rainfall-runoff event characteristics after 1996. Compared with the period 1971−1996, precipitation decreased slightly after 1996, whereas runoff depth, runoff peak, and hydrograph shape index declined by 24.9%, 30.6%, and 20.5%, respectively. Concurrently, the correlation between precipitation and runoff weakened, and the outflow process became increasingly important for runoff. Furthermore, cropland exhibited the most significant decline, decreasing from 758.0 km² in 1980 to 560.4 km² in 2017, with the converted area primarily transitioning to forest, shrubland, and grassland. This conversion of cropland to shrubland and grassland shifted the runoff process from Hortonian overland flow (HOF) to saturation overland flow (SOF). Consequently, the percentage of the area dominated by HOF decreased by 16.9% from 1980 to 2017. Meanwhile, grassland restoration in the southern part of the basin increased the proportion of SOF by 12.1%. Under comparable rainfall conditions, rainfall-runoff characteristics within the same region exhibited substantial variability in response to shifts in runoff processes. These findings provide novel insights into hydrological modeling and water resources management in semi-arid basins.