U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Microtopography Determines Active Layer Depths Responses to Temperature and Precipitation at the NGEE-Arctic’ Barrow Experimental Observatory Sites

William J. Riley
Lawrence Berkeley National Laboratory

Highlight

21 Dec 2017

Landscape features determine thermal and hydrological responses in polygonal tundra

The Science
A research team from Lawrence Berkeley Laboratory applied a well-tested three-dimensional coupled biogeochemistry, hydrology, vegetation, and thermal model, called ecosys,  to polygonal tundra sites in Alaska to quantify and scale the effects of microtopography on Active Layer Depth (ALD), soil hydrology, and energy exchanges with the atmosphere. They found that interannual variation in ALD was more strongly related to precipitation than air temperature, contrary to what most large-scale models assume. Further, they found excellent spatial scaling results from sub-meter to landscape scales using our modeling approach.

The Impact
The LBNL team demonstrated excellent agreement between predictions and NGEE-Arctic observations of soil temperature and moisture and eddy covariance energy exchanges with the atmosphere. The estimates of the importance of precipitation energy content on thaw depth have important implications for predictions of future thermal, hydrological, and biogeochemical states in the Arctic. Finally, these results imply needed improvements to the DOE E3SM land model (ELMv1-ECA).

Summary
Current ESM land model representations of high-latitude thermal and hydrological states ignore several important processes and representation of sub-grid scale heterogeneity, and therefore predicted interactions with the atmosphere remain uncertain. The LBNL  analysis here, which combined fine-scale modeling and comparison to a wide range of NGEE-Arctic measurements, demonstrates a viable approach to representing fine-scale processes and links to landscape scale dynamics. Together these findings challenge widely held assumptions about controls on landscape-scale energy and water budgets, and are motivating their ongoing improvements to the DOE land model (ELMv1-ECA).

BER PM Contacts
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact
William J. Riley
Lawrence Berkeley National Laboratory, wjriley@lbl.gov

Funding
This research was supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE Arctic) project.

Publications
Grant, R. F., Z. A. Mekonnen, W. J. Riley, H. M. Wainwright, D. E. Graham, and M. S. Torn (2017), Mathematical Modelling of Arctic Polygonal Tundra with Ecosys: 1. Microtopography Determines How Active Layer Depths Respond to Changes in Temperature and Precipitation, JGR-Biogeosciences, 10.1002/2017JG004035.

LBNL NGEE-Arctic

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