Advances in Earth Science ›› 2013, Vol. 28 ›› Issue (11): 1269-1275.

• Orginal Article • Previous Articles     Next Articles

Spatial and Temporal Distribution and Variations in the Near-surface Soil Freezing Days across China, 1956-2006

Wang Kang 1, Zhang Tingjun 1, 2, *   

  1. 1.Key Laboratory of Western China’s Environmental Systems (Ministry of Education), Lanzhou University,Lanzhou 730000, China; 2.College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China; 3.National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, CO 80309, USA
  • Received:2013-06-13 Online:2013-11-10 Published:2013-11-10

Wang Kang,Zhang Tingjun,*. Spatial and Temporal Distribution and Variations in the Near-surface Soil Freezing Days across China, 1956-2006[J]. Advances in Earth Science, 2013, 28(11): 1269-1275.

Using surface soil daily minimum temperature from 845 meteorological stations across China, the long-term (1971-2000) mean and spatial distribution of the near-surface soil freezing days were estimated with annual values of the number of nearsurface soil freezing days. The time series for the number of freezing days were constructed and compared with air temperatures in the same period.Resultsshowed that longterm mean value in the number of the nearsurface soil freezing days increased with the increasing latitudes and altitudes over China. Near-surface soils were frozen for more than 200 days in the QinghaiTibet Plateau, northern Xinjiang and northeast of China. The boundaries of permafrost zones coincide with the contour of (220±10) days of near-surface soil freezing. Using the mean number of 15 days of near-surface soil freezing as criterion, we found that the southern boundary of seasonally frozen ground is around the 25°N line, and the regions south of 22°N are essentially unfrozen regions. The timeseries of the number of freezing days showed a significant linear trend with change with a slope of -0.22days/year over a period from 1956 through 2006. After the 1990s, the linear slope was up to -1.02 days / year, indicating that the rate of decrease in the number of near-surface soil freezing days has accelerated. Changes in the number of nearsurface soil freezing were in a negative correlation with air temperature, i.e., the number of near-surface soil freezing days decreases with increase in air temperature.Backgroundcolor represents the contour values of the departure of near-surface soil freezing days from the 1971-2000 mean; Black dashed line is the boundary of permafrost regions, red dashed line is the boundary between frozen and unfrozen ground regions in China
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