Articles | Volume 11, issue 3
Research article
05 May 2017
Research article |  | 05 May 2017

Response of seasonal soil freeze depth to climate change across China

Xiaoqing Peng, Tingjun Zhang, Oliver W. Frauenfeld, Kang Wang, Bin Cao, Xinyue Zhong, Hang Su, and Cuicui Mu

Abstract. The response of seasonal soil freeze depth to climate change has repercussions for the surface energy and water balance, ecosystems, the carbon cycle, and soil nutrient exchange. Despite its importance, the response of soil freeze depth to climate change is largely unknown. This study employs the Stefan solution and observations from 845 meteorological stations to investigate the response of variations in soil freeze depth to climate change across China. Observations include daily air temperatures, daily soil temperatures at various depths, mean monthly gridded air temperatures, and the normalized difference vegetation index. Results show that soil freeze depth decreased significantly at a rate of −0.18 ± 0.03 cm yr−1, resulting in a net decrease of 8.05 ± 1.5 cm over 1967–2012 across China. On the regional scale, soil freeze depth decreases varied between 0.0 and 0.4 cm yr−1 in most parts of China during 1950–2009. By investigating potential climatic and environmental driving factors of soil freeze depth variability, we find that mean annual air temperature and ground surface temperature, air thawing index, ground surface thawing index, and vegetation growth are all negatively associated with soil freeze depth. Changes in snow depth are not correlated with soil freeze depth. Air and ground surface freezing indices are positively correlated with soil freeze depth. Comparing these potential driving factors of soil freeze depth, we find that freezing index and vegetation growth are more strongly correlated with soil freeze depth, while snow depth is not significant. We conclude that air temperature increases are responsible for the decrease in seasonal freeze depth. These results are important for understanding the soil freeze–thaw dynamics and the impacts of soil freeze depth on ecosystem and hydrological process.

Short summary
Previous research has paid significant attention to permafrost, e.g. active layer thickness, soil temperature, area extent, and associated degradation leading to other changes. However, less focus has been given to seasonally frozen ground and vast area extent. We combined data from more than 800 observation stations, as well as gridded data, to investigate soil freeze depth across China. The results indicate that soil freeze depth decreases with climate warming.