Abstract
On the basis of observed soil freeze depth data from 14 meteorological stations on the Three Rivers Source Region (TRSR) in China during 1960 to 2014, trends in the freeze depth, first date, last date, and duration of frozen soil were analyzed, together with other meteorological variables, such as air temperature, snow depth, and precipitation, observed at the same locations. The results showed the following. (1) A continuous, accelerated decreasing trend in freeze depth appeared in the TRSR during the 1985–2014 and 2000–2014 periods, compared with that during the 1960–2014 period. (2) The freeze first date had been delayed and the freeze last date had been advanced significantly. The advanced trends in freeze last date were more significant than the delayed trends in freeze first date. The freeze duration also experienced an accelerated decrease. (3) The freeze depth and period were strongly affected by air temperature, thawing index, and soil moisture (precipitation), but not by snow. The freeze depth, freeze first date, freeze last date, and duration also influenced each other. (4) These decreasing trends in freeze depth and duration are expected to continue given the increasing trends in air temperature and precipitation in this region.
Highlights
Frozen soil is a sensitive indicator of climate change
The advanced trends in freeze last date were more significant than the delayed trends in freeze first date
The freeze depth and period of frozen soil, which are strongly affected by air temperature, snow, soil moisture, and vegetation [22,23,24,25,26], are important indexes of frozen soil conditions
Summary
Frozen soil is a sensitive indicator of climate change. It is highly correlated with air temperature [1,2,3]. A major obstacle to understanding the response of frozen soil to climate change, as well as the interactions between the soil and the atmosphere, is the lack of long-term observations For this reason, other climatic indicators, such as soil temperature and minimum air temperature, remote sensing data, and numerical simulation, are exploited to characterize the freeze depth and period of frozen soil. Frauenfeld et al [27] employed a linear interpolation method to determine the depth of the 0∘C isotherm based on soil temperature data measured between 0.2 m and 3.2 m depth, using mean monthly soil temperature data collected between 1930 and 1990 from 242 stations located throughout Russia They found that the active layer of permafrost increased by 20 cm and the depth of the seasonal
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