Abstract
Knowledge of the spatiotemporal dynamics of the soil temperature in cold environment is key to understanding the effects of climate change on land–atmosphere feedback and ecosystem functions. Here, we quantify the recent thermal status and trends in shallow ground using the most up-to-date data set of over 457 sites in Russia. The data set consists of in situ soil temperatures at multiple depths (0.8, 1.6, and 3.2 m) collected from 1975 to 2016. For the region as a whole, significant soil warming occurred over the period. The mean annual soil temperature at depths of 0.8, 1.6, and 3.2 m increased at the same level, at ca 0.30–0.31 °C/decade, whereas the increase in maximum soil temperature ranged from 0.40 °C/decade at 0.8 m to 0.31 °C/decade at 3.2 m. Unlike the maximum soil temperature, the increases in minimum soil temperature did not vary (ca 0.25 °C/decade) with depth. Due to the overall greater increase in maximum soil temperature than minimum soil temperature, the intra-annual variability of soil temperature increased over the decades. Moreover, the soil temperature increased faster in the continuous permafrost area than in the discontinuous permafrost and seasonal frost areas at shallow depths (0.8 and 1.6 m depth), and increased slower at the deeper level (3.2 m). The warming rate of the maximum soil temperature at the shallower depths was less than that at the deeper level over the discontinuous permafrost area but greater over the seasonal frost area. However, the opposite was found regarding the increase in minimum soil temperature. Correlative analyses suggest that the trends in mean and extreme soil temperatures positively relate to the trends in snow cover thickness and duration, which results in the muted response of intra-annual variability of the soil temperature as snow cover changes. This study provides a comprehensive view of the decadal evolutions of the shallow soil temperatures over Russia, revealing that the temporal trends in annual mean and extreme soil temperatures vary with depth and permafrost distribution. • Significant warming of shallow ground occurred in Russia during 1975–2016. • Trends in soil temperature vary with depth in different frost-related areas. • For the region as a whole, the intra-annual variability of soil temperature increased. • Trends in soil temperature significantly respond to changes in snow cover.
Highlights
The soil thermal regime is one of the most fundamental factors influencing terrestrial processes in cold regions (Barry and Gan, 2011; Karjalainen et al, 2019; Streletskiy et al, 2017)
It is found that MAST was, in general, higher than mean annual air temperature (MAAT), accounting for 0.64 of MAAT at all sites (Fig. 5a)
Relations between the trends in temperature (MAST, Tmin) and SSD are stronger than the trends in SCD with a higher coefficient of determination (R2), indicating that the changes in snow cover depth may be more influential in affecting the soil temperature than the SCD
Summary
The soil thermal regime is one of the most fundamental factors influencing terrestrial processes in cold regions (Barry and Gan, 2011; Karjalainen et al, 2019; Streletskiy et al, 2017). The changing soil temperatures have already had a significant impact on biogeochemical functions, soil hydrology, geomorphologic processes, and infrastructure stability (Cheng and Wu, 2007; Fountain et al, 2012; Grosse et al, 2016; Hjort et al, 2018). Permafrost – ground that remains frozen for at least two consecutive years – is mainly distributed across polar and high altitude areas, which are some of the most climate-sensitive places on Earth (Chadburn et al, 2017; Gruber, 2012; Romanovsky et al, 2010; Vieira et al, 2010; Zhao et al, 2010). Compared with research on permafrost areas, the seasonal frost area – where the ground experiences at least 15 days of freezing per year – has received less attention (Tar nocai et al, 2009; Tingjun, 2005)
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