Assessment and Projection of Ground Freezing–thawing Responses to Climate Change in the Upper Heihe River Basin, Northwest China

Study region: Upper Heihe River Basin, Northwest China. Study focus: We investigated potential climate change under three Representative Concentration Pathways (RCP 2.6, 4.5, and 8.5) and their impacts on frozen ground in the upper Heihe River Basin using the ensemble climate data from eight general circulation models and the Soil and Water Assessment Tool (SWAT). New hydrological insights for the region: Air and ground freezing indices declined significantly during the baseline period (1976-2015), whereas the thawing indices increased, indicating the heat accumulation in study area. The frost depth, which refers to the potential frost depth of active layer in permafrost areas and the maximum frost depth in seasonally frozen areas, decreased significantly at the rate of 3 cm/10 yr. The SWAT-simulation and gray relational analysis revealed that soil water was controlled by precipitation and frost depth in spring and autumn. Compared to that of the baseline, the projected frost depth is projected to decline by 0.07-0.1 m during the near future (2020-2059) and 0.08-0.36 m for the far future (2060-2099). In addition, we developed a long-term warning system, which indicates that the degree of frozen ground degradation would be mild during the near future and would be severe for the far future under RCP 8.5. This study provides valuable insights into the protection of frozen-ground in the Upper Heihe River Basin.