Quantifying the impacts of climate change and human activities on hydrological regime in Jinsha River, China

Climate change and human activities have altered natural hydrological regimes, posing critical threats to river ecosystems. Existing studies predominantly focus on characterizing hydrological changes but lack systematic quantification of driving factors, particularly the relative contributions of climate and human impacts, which limits the understanding of ecological consequences. This study addresses this gap by integrating SWAT-based natural runoff restoration and attribution analysis of hydrological regime changes. Firstly, the Mann-Kendall (M-K) and Pettitt methods were applied to detect change points in the runoff series, dividing it into natural and variation periods. The SWAT model was then employed to restore natural runoff during the variation period. Secondly, the hydrological regime was assessed using the indicators of hydrologic alteration (IHA). To address redundancy among the 33 IHA parameters, principal component analysis (PCA) was utilized to identify ecologically relevant hydrologic indicators (ERHIs). Changes in these ERHIs were quantified to calculate the contribution rates of climate change and human activities to hydrological regime alterations. The hydrological control station of Jinsha River Basin, i.e., Xiangjiaba (XJB) was selected as study object. The results demonstrated that change point was detected in 1986, dividing the runoff series into natural (1961-1986) and variation (1987-2020) periods. The SWAT model effectively reconstructed natural daily runoff during 1987-2020, achieving Nash-Sutcliffe efficiency values of 0.79 and 0.76 for calibration and validation, respectively. The overall hydrological alteration degree was 31 %, indicating a low alteration of hydrological regime at XJB station. Six ERHIs were selected, including the 7-day maximum flow, 7-day minimum flow, May median flow, June median flow, number of reversals, and fall rate. Climate change dominated high-flow and seasonal indicators reductions (e.g., 61.6 % contribution to 7-day maximum flow decline), while human activities drove low-flow increases (e.g., 55.1 % contribution to 7-day minimum flow rise). These findings can provide actionable insights for balancing water resource development and ecological conservation in regulated basins under dual climatic and anthropogenic pressures.