Runoff evolution responses to climate change: A case study in the headwater area of Yellow River, China

The headwater area of the Yellow River (HAYR) plays an important role in runoff generation for the entire Yellow River basin. However, the runoff patterns within this crucial source region have been experiencing significant changes over the past decades. These changes have made pronounced impacts on the inter-annual and even intra-annual distributions of runoff, especially for the unique double flood peaks (DFP; one peak appears in July and another in September). This study comprehensively demonstrated the runoff evolution in HAYR and its future projection under the background of climate change based on multi-source data analysis and hydrologic simulation. First, we used three mainstream precipitation datasets (i.e., CHM_PRE, CMFD, and TPHiPr) to drive the land surface hydrologic model (i.e., VIC) in the large-scale basin with sparse ground observation. Our simulation results show that the CHM_PRE-driven VIC exhibits the best performance in six experimental combinations. Thus, we adopted the simulation mode of CHM_PRE-driven VIC to quantify the impacts of climate change and human activities on runoff. It was found that climate change was the primary driver for the runoff reduction after the year of 1990 with a contribution of 81.14 %, while human activities only account for 18.86 %. But human activities likely have a larger impact on runoff during those dry periods. Notably, climate change has reduced the peak discharge and shifted the peak time in that, the main peak occurred earlier and the secondary peak appeared later. Subsequently, projections based on future scenarios of Global Climate Models (GCMs) suggest a declining trend in runoff, along with a noticeable periodicity, showing a cycle of approximately 40 years. Finally, the diagnosis of the significance level of flood peaks indicates that the increasing inter-annual variability and the more frequent intra-annual fluctuations will appear in the future runoff changes. This study is expected to enable basin managers to better optimize the water resource allocation and make well-informed practice decisions for the HAYR under global climate change.