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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

Highlight

21 December 2017

Landscape features determine thermal and hydrological responses in polygonal tundra

The Science
A research team from Lawrence Berkeley Laboratory (LBNL) 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 submeter to landscape scales using the team's modeling approach.

The Impact
The LBNL team demonstrated excellent agreement between predictions and Next-Generation Ecosystem Experiments (NGEE)–Arctic project 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 U.S. Department of Energy (DOE) Exascale Earth System Model (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 subgrid 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).

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, 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. “Mathematical modelling of Arctic polygonal tundra with Ecosys: 1. Microtopography determines Hhow active layer depths respond to changes in temperature and precipitation.” JGR-Biogeosciences 122(12), 3161–3173 (2017). [DOI:10.1002/2017JG004035]

LBNL NGEE-Arctic

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