Impact of climatic and vegetation dynamic change on runoff over the Three Rivers Source Region based on the Community Land Model

The Three Rivers Source Region (TRSR), the headwater region of the Yellow River, the Mekong River, and the Yangtze River, plays a significant role in water resources, food security, economy, and society in the downstream areas. This study applied a series of offline regional simulations of the Community Land Model (CLM5.0) over the TRSR to evaluate the impacts of regional climate and vegetation change on runoff. Firstly, we evaluated the performance of runoff depth using CLM5.0, the Nash-Sutcliffe efficiency between the simulated and observed runoff of TNH and ZMD gage stations are 0.56 and 0.51, respectively. The climate on the TRSR shows a warming and wetting trend, with the fastest warming rate in DJF (December, January, and February) and the fastest wetting rate in JJA (June, July, and August). Runoff increases in most of the TRSR with increased precipitation and decreases in the southeast of the Yellow River Source Region (YRSR). With increasing temperature, the simulated runoff shows a decreasing trend, while runoff tends to increase with precipitation enhancement over the TRSR. The results indicated that precipitation is the dominant factor affecting evapotranspiration (ET) and runoff, whilst the contribution of increasing temperature to runoff is 12%, which plays a regulatory role in the increased streamflow. In addition, Dynamic Global Vegetation Model (DGVM) in CLM5.0 was used to study the impact of vegetation change on runoff. Compared to the static vegetation, the simulated leaf area index (LAI) from the DGVM shows an increasing trend in most regions of the TRSR and the runoff in the TRSR decreases by 33%.