Local-Scale Variability of Soil Temperatures and Controlling Factors in a Discontinuous Permafrost Region

The Science

Soil thermal states in the Arctic region are diverse, complicating the understanding of permafrost systems’ response to climate change. Researchers focused on a small region and measured 1-year soil temperature change at different depths from dense locations. Results show that soil thermal states vary across the region, even with uniform weather conditions. Large differences in winter soil temperatures cause the differences in annual soil temperatures. The main drivers of these differences are diverse plant and snow distribution causing different winter cooling processes.

The Impact

Understanding the local spatial distribution of soil temperatures is critical to accurately predicting permafrost environment response to climate change. This work measures high-resolution soil temperature data and builds a linkage between soil temperatures and aboveground properties that can help researchers develop products that use aboveground images to estimate soil temperatures. The study also provides valuable data and knowledge to validate Earth system models.

Summary

Soil temperatures in the permafrost regions exhibit strong spatial and temporal variability that cannot be explained by weather forcing only. By acquiring high-resolution temperature data, the study aims to understand the local heterogeneity of soil thermal dynamics and their controlling factors. At 45 discrete locations across a relatively small watershed, researchers measured depth-resolved soil temperature over 1 year at 5- or 10-cm intervals up to 85 cm depth. Results showed spatial variability in winter temperatures controls the spatial variability in mean annual temperatures.

The study demonstrates that mean annual or winter ground surface temperatures are good indicators of mean annual ground temperature at 85 cm. Soils clustered as cold, intermediate, or warm groups closely match their co-located vegetation (graminoid tundra, dwarf shrub tundra, and tall shrub tundra, respectively). The spatial variability in mean annual soil temperature is primarily driven by diversity in snow cover, which induces variable winter insulation and soil thermal conduction. These effects further extend to the subsequent summer by causing variable latent heat exchanges. Finally, the study demonstrates the challenges of predicting soil temperatures from snow depth and vegetation height alone by considering the complexity observed in field data and reproduced in a model sensitivity analysis.

Principal Investigator

Chen Wang
Lawrence Berkeley National Laboratory
[email protected]

Co-Principal Investigator

Baptiste Dafflon
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the Biological and Environmental Research program within the U.S. Department of Energy Office of Science as part of the Next-Generation Ecosystem Experiments Arctic (NGEE Arctic) project.

References