Decadal Changes in Soil and Atmosphere Temperature Differences Linked With Environment Shifts Over Northern Eurasia

Miska Luoto,Liangzhi Chen,Juha Aalto

doi:10.1029/2020jf005865

Abstract

AbstractThe difference between soil and air temperatures (ΔT) in a specified time is dependent on meteorological conditions, properties of soil and land covers. Understanding ΔT is critical in assessing land–atmosphere thermal interactions in changing environment. However, systematic knowledge of interannual variations and responses of ΔT to the environmental changes (e.g., snow cover and soil moisture) at decadal scales remain limited. Here, variations of the mean annual air and soil temperatures, and ΔT were investigated at 217 sites in northern Eurasia during 1981–2015. It is found that changes in the mean annual air and soil temperatures were inconsistent as the average increase in soil temperature was generally less than that of air. The relationships between trends in soil and air temperatures were significant in the upper ground (0.2 and 0.8 m) over the seasonal frost region but insignificant in the permafrost regions and deeper ground. During the period, widespread changes in ΔT occurred and closely responded to the environmental changes, but the relationships varied with soil depth. Among the tested factors, trends in snow cover thickness dominantly control trends in ΔT, followed by trends in snow cover duration and solar radiation. Both linear and nonlinear analyses indicate enhanced relationships between trends in snow depth and ΔT as depth increases. This study provides the first view of decadal trends in ΔT and conjunctions with the environmental changes during 1981–2015 over northern Eurasia. The findings are relevant to quantify land–atmosphere thermal interactions given impacts of future environmental changes.

Highlights

The soil temperature is an integrator of hydrothermal processes and their interactions near ground surface and within soil
The average increase in mean annual soil temperature is slightly lower than the increase in mean annual air temperature except at a depth of 0.2 m (0.44°C decade−1), which is greater than the mean annual air temperature increase (0.36°C decade−1) in the seasonal frost region (Figure 2)
Inconsistent warming rates of the mean annual air and soil temperatures lead to interannual variations of ΔT, which are spatially heterogeneous across northern Eurasia

Summary

Introduction

The soil temperature is an integrator of hydrothermal processes and their interactions near ground surface and within soil. Subsurface soil temperature differs from ambient air temperature by the presence of environmental elements, such as snow cover, vegetation, soil organic materials and moisture, and solar radiation (Aalto et al, 2018; Frenne et al, 2019; Grundstein et al, 2005; Lenoir et al, 2017; Zhang, 2005). The difference between soil and air temperatures (ΔT) substantially affects freeze–thaw depth of frost-related ground and temperature-sensitive processes in biogeochemical and biogeophysical functions, such as soil carbon decomposition, vegetation growth, and snow cover retreat Long-term interannual variations of ΔT and its response to the changing environmental conditions are little known yet as most previous efforts have been devoted to ΔT and its controls at seasonal (or diurnal) scale (Aalto et al, 2018; Bartlett et al, 2004; Wang et al, 2017)

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Discussion

Conclusion