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Changes of Soil Thermal Regimes in the Heihe River Basin Over Western China
Author(s): Qingfeng Wang, Tingjun Zhang, Xiaoqing Peng, Bin Cao and Qingbai Wu
Source: Arctic, Antarctic, and Alpine Research, 47(2):231-241.
Published By: Institute of Arctic and Alpine Research (INSTAAR), University of Colorado
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Arctic, Antarctic, and Alpine Research, Vol. 47, No. 2, 2015, pp. 231–241
Changes of soil thermal regimes in the Heihe River
Basin over Western China
Bin Cao2 and
Qingbai Wu1 1State Key Laboratory of Frozen Soil
Engineering, Cold and Arid Regions
Environmental and Engineering Research
Institute, CAS, 320 Donggang West Road,
Lanzhou, Gansu Province 730000, P. R.
China 2MOE Key Laboratory of Western China’s
Environmental Systems, College of Earth and Environmental Sciences, Lanzhou
University, Lanzhou 730000, P.R. China 3Corresponding author: email@example.com
Soil thermal regimes in seasonally frozen ground and permafrost regions, especially soil temperature and seasonal freeze/thaw processes, play an essential role in ecosystems and ecohydrological processes (Zhang et al., 2003; Frauenfeld et al., 2004; Zhang et al., 2013). They also affect water exchange between the ground surface and atmosphere, which ultimately has impacts on weather and climate systems through changes in surface energy balance (Jin and Li, 2009; Zhou et al., 2013).
Soil temperature is linked to climate through the top layer of the soil that freezes and thaws seasonally, vegetation, and snow cover (Lachenbruch and Marshall, 1986). In permafrost regions, degree days of freezing/thawing for air or surface (DDF a /DDT a or DDF s /DDT s ) are used to predict active layer thickness (ALT) (Nelson et al., 1997; Shiklomanov and Nelson, 2002; Zhang et al., 2003, 2005) and spatial distribution of permafrost (Nelson and Outcalt, 1987; Ran et al., 2012). On the other hand, ALT is an indicator of climate change (Nelson et al., 1997; Brown et al. 2000; Zhang et al., 2003, 2007; Osterkamp, 2007; Frauenfeld et al., 2007). Similarly, the thickness of seasonally frozen ground can also be used to investigate long-term climate and environment changes (Frauenfeld and Zhang, 2011).
Permafrost and seasonally frozen ground are well underlain in the Heihe River Basin (Zhou et al., 2000), and permafrost region occupies ~10.5% of the basin (Wang et al., 2013).
The snow cover zone and tundra are the main catchment areas for the Heihe River Basin, accounting for ~80% of the basin-wide runoff (Wang et al., 2009). Caused by recent global warming, air temperature increases significantly in the Qilian
Mountains (Lan et al., 2001; Zhang and Guo, 2002; Yin et al., 2009). Construction and engineering activities have increased in recent years. These changes necessitate an investigation of the soil thermal regime conditions (such as soil temperature and soil seasonal freeze/thaw processes) in the Heihe River Basin in order to understand ecohydrological processes, resource development, and climate change.
Most research on the freeze/thaw processes in cold regions focuses mainly on permafrost regions. Research on the coastal plain adjacent to the Beaufort Sea in Alaska shows that ALT increased from the coast inland from 1986 through 1993 (Romanovsky and Osterkamp, 1997). Summer precipitation could cause the thaw front to move rapidly in the active layer due to sensible heat carried by the percolating rainwater downward (Hinkel et al., 1997). It is indicated that ALT patterns had primary relationship with physiographic features through affecting surface and subsurface hydrological processes in the Kuparuk River
Basin in northern Alaska (Nelson et al., 1998). Compared with air temperatures, ground temperatures in 1979–1999 exhibited a closer relationship with thickness and duration of snow cover at the lower limit of alpine permafrost in the Marmot Basin, Canada (Harris, 2001). ALT showed a decline from 1995 through 2007 on the North Slope of Alaska, which was generally related to the decline in summer air temperature. Streletskiy et al. (2008) found that the maximum values of ALT in the Alaskan Arctic were recorded accordingly in the years with the warmest summers. Changes in ALT and the maximum thickness of seasonally frozen ground (MTSFG) in the Eurasian high latitudes have also been investigated. During the 1956–1990 period, ALT has thickened significantly by ~20 cm, while MTSFG decreased by 34 cm in Russia (Frauenfeld et al., 2004). Evaluating the MTSFG at 387 sites of seasonally frozen ground for the period 1930–2000,
Frauenfeld and Zhang (2011) found that the MTSFG significantly decreasd by 31.9 cm at a rate of –4.5 cm decade–1.
Investigation of the changes in soil thermal regimes is essential to the understanding of ecohydrological processes, resource development, and climate change. We use soil temperatures from 12 meteorological stations of the China Meteorological Administration in the Heihe River Basin to estimate soil seasonal freeze depth, the onset and end dates of soil freeze, and the duration of soil freeze. Based on the characteristics of the soil temperature in the seasonal freezing layer, the freeze/thaw processes of this layer were divided into four stages: the winter freezing stage, spring thawing stage, summer warming stage, and autumn cooling stage. Spring, summer, autumn, and winter ground surface temperatures in the basin exhibit significant increasing trends in 1972–2006, of 0.65 °C decade–1, 0.73 °C decade–1, 0.48 °C decade–1, and 0.44 °C decade–1, respectively. Mean annual soil temperature at 0.0–0.20 m depths reveals an increasing trend of 0.58–0.63 °C decade–1 in 1972–2006. The onset date of soil freeze, the end date of soil freeze, and the duration of soil freeze in 1972–2006 exhibit a statistically significant trend of +2 days decade–1, –4 days decade–1, and –6 days decade–1, respectively. The maximum thickness of the seasonally frozen ground for 1960–2007 reveals a statistically significant trend of –4.0 cm decade–1 and a net change of –19.2 cm for the 48-year period. These are all related to the increase in spring, summer, autumn, and winter air temperature and the mean annual air temperature in the basin, a possible result of global warming. 232 / ARCTIC, ANTARCTIC, AND ALPINE RESEARCH