Impacts of precipitation changes and human activities on annual runoff in the Yihe River basin from 1951 to 2020

The analysis of runoff evolution trends and quantitative assessment of the impacts from both climate change and human activities on annual runoff are critically important for advancing sustainable water management, supporting ecological conservation initiatives, and promoting long-term socioeconomic development within river basins. This study focuses on the Yihe River basin and utilizes long-term observed data of runoff and precipitation covering the period from 1951 to 2020. The primary objectives are to detect and characterize trends in annual precipitation and runoff, to quantify the respective contributions of climatic variation and anthropogenic disturbances to observed changes in runoff, and to elucidate the underlying mechanisms governing runoff evolution in the basin. To achieve these objectives, the Mann-Kendall trend test was employed to statistically identify significant trends in the hydro-meteorological time series. A time-series comparison method, specifically the double mass curve technique, was applied to diagnose periods of consistency and change in the precipitation-runoff relationship. Furthermore, an empirical statistical model linking precipitation to runoff was developed and calibrated for a defined baseline period, during which human influence was considered minimal. This established model was subsequently used to simulate naturalized runoff during a subsequent impacted period, enabling the separation of climatic and anthropogenic effects. The results reveal a statistically significant declining trend in both annual precipitation and annual runoff over the seven-decade study period. A major finding is the identification of a distinct shift in the dominant drivers of runoff change around the mid-1960s. Consequently, the entire study duration was partitioned into two phases for detailed analysis: a baseline period (1951-1965) and an intervention period (1966-2020). During the baseline period, inter-annual variability in runoff was predominantly governed by natural precipitation fluctuations. In contrast, the intervention period was characterized by a substantial anthropogenic imprint on the hydrological regime. Intensive human activities-including but not limited to the construction and operation of water conservancy projects, large-scale abstraction for water supply, implementation of various ecological restoration projects, and significant transformations in land use and land cover-were identified as the principal factors responsible for the notable reduction in annual runoff. Quantitative attribution analysis based on the empirical model indicates that the magnitude of runoff reduction attributable to human activities significantly exceeds that caused by precipitation change alone during the intervention period.nIn conclusion, this research underscores the increasing dominance of human activities in reshaping the hydrological cycle of the Yihe River basin, overshadowing the role of natural climatic variability in recent decades. The quantitative findings offer valuable insights and a robust scientific foundation for informing future policy-making, guiding ecological protection strategies, and optimizing water resources allocation and management practices in the basin and other similar regions facing comparable challenges.