December 11, 2020

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Thawing Permafrost may Lead to Cooler Streams in Summer

Observations and modeling suggest that thawing permafrost increases the contribution of deeper and cooler groundwater to streams.

Magnitude of groundwater flux colored by stream temperature from hillslope models assuming continuous, discontinuous and no permafrost.

[Reprinted under a CC BY-NC-ND 4.0 license from Sjöberg, Y., et al. “Permafrost promotes shallow groundwater flow and warmer headwater streams.” Water Resources Research 57, e2020WR027463 (2021). https://creativecommons.org/licenses/by-nc-nd/4.0/]

The Science

Permafrost influences the flow of water in Arctic landscapes and, as a result, has the potential to influence streamflow and stream temperature. Analysis of observations from 11 headwater streams in Alaska show that July water temperatures were higher in catchments with more near‐surface permafrost. Hillslope-scale simulations using a fully coupled cryohydrology model show that observed trends are consistent with thaw-induced flowpath changes. Specifically, degrading permafrost leads to deeper flow paths, which buffers seasonal extremes in air temperature and leads to cooler streams in the summer.

The Impact

Stream temperature is an important water quality variable for aquatic ecosystems. Stream warming can affect fish populations and drive changes in species composition. This sensitivity leads to significant concern about stream warming in response to climate change. Analysis of headwater stream observations found that in Arctic regions, thaw-induced changes in water flow paths may partially counter the effects of increasing air temperatures and result in cooler streams than would be expected from increasing air temperatures alone.

Summary

Daily stream temperatures in July in headwater streams from the Noatak River Basin were found to be positively correlated with percent permafrost coverage. Researchers used the integrated surface/subsurface code Amanzi-ATS model configured in cryohydrology mode to investigate whether the impact of permafrost on flow path depth could cause a similar pattern in temperatures of groundwater discharging from hillslopes to streams. The model simulates surface energy and water balances, snow, and subsurface water and energy dynamics. The numerical experiments used two‐dimensional hillslopes with varying permafrost extents. Researchers found that hillslopes with continuous permafrost have shallower flow paths compared to hillslopes with no permafrost. The deeper flow paths in permafrost‐free simulations buffer seasonal temperature extremes so that summer groundwater discharge temperatures are highest with continuous permafrost. Results suggest that permafrost thawing alters groundwater flow paths and can lead to decreases in summer stream temperatures and reductions in evapotranspiration in headwater catchments.

Principal Investigator

Scott Painter
Oak Ridge 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 funded by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas) under grant number 2015-00790 (Y. Sjöberg). It was also supported by the Changing Arctic Ecosystems Initiative of the Wildlife program of the U.S. Geological Survey Ecosystems Mission Area; the National Park Service’s Arctic Inventory and Monitoring Network; and staff from the Western Arctic Parklands in Kotzebue, Alaska. Oak Ridge National Laboratory’s (ORNL) contribution to this work was supported by the Next-Generation Ecosystem Experiment—Arctic (NGEE-Arctic) project. The NGEE-Arctic project is supported by the Office of Biological and Environmental Research (BER) in the U.S. Department of Energy’s (DOE) Office of Science.

Related Links

References

Sjöberg, Y., et al. "Permafrost Promotes Shallow Groundwater Flow and Warmer Headwater Streams." Water Resources Research 57 (2), e2020WR027463  (2021). https://doi.org/10.1029/2020WR027463.