Subsurface thermal and hydrological changes between forested and clear-cut sites in the Oregon Cascades
University of Utah
Thermal Geophysics
Research Group
Michael G. Davis1*, Ronald S. Waschmann2, Robert N. Harris3 and David S. Chapman1
Department of Geology and Geophysics
http://thermal.gg.utah.edu
2U.S.
1Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA
Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Laboratory, Western Ecology Division, Corvallis, Oregon 97333, USA
3College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA
*E-mail: michael.g.davis@utah.edu; Phone: (801) 581-3588; http://thermal.gg.utah.edu/~mgdavis/
Introduction
The Cascades of the US Pacific Northwest are a climatically sensitive
area. Projections of continued winter warming in this area are expected to
induce a switch from a snow-dominated to a rain-dominated winter precipitation regime with a likely impact on subsurface thermal and hydrological
regimes. Such changes to the ecosystem may also be linked to changes
in land cover, resulting in amplified subsurface temperatures and changing
the timing and availability of subsurface water. To monitor changing climatic conditions in this region, the Environmental Protection Agency established pairs of meteorological stations over the Santiam Pass, Cascades
Mountains, Oregon, USA, at 5 locations spanning elevations between 500
to 1200 m in the late 1990s. Each location comprises two separate meteorological towers; one under the old-growth coniferous forest canopy and
the other in a near by opening or clear-cut. One purpose of the paired stations is to understand the influence of the forest canopy and the developing
clear-cut vegetation on the seasonal and annual soil moisture and temperature at each station. We report a comparison of observations between
paired stations and a comparison between observations and a land surface
model. Preliminary results indicate that open areas have higher air and
soil temperatures and receive greater amounts of precipitation and incoming radiation. These conditions are contrasted with the muted conditions
under the forest canopy. The results have implications for understanding
surface energy exchanges, their impact on the subsurface thermal and hydrological regimes, and possible feedbacks to the climate system as a
function of time, space and land cover.
Site Comparisons
Open
Site
PAR
Wind
Tair
Rain
Tsoil
RH
Annual Differences
Closed
Site
Snow
PAR
Moisture
Wind
Tair
Rain
Tsoil
RH
Site Photos
RH
Snow
PAR
Rain
Snow
Moisture
Wind
Tsoil
Moisture
Annual difference between the open and closed canopy sites at Soapgrass
Mountain for air temperature, relative humidity, solar radiation, precipitation,
snow cover, wind speed, soil temperature, and soil moisture for the year
2000.
Contrast between the open (left) and closed (right) canopy sites at Soapgrass Mountain for
air temperature, relative humidity, solar radiation, precipitation, snow cover, wind speed, soil
temperature, and soil moisture from late 1997 through 2005.
Location Map
Tair
Open Closed
Land Surface Modeling
Snow
Moisture z=20 cm
Transpiration
Canopy Water
Evaporation
Precipitation
Condensation
Toad Creek
on
vegetation
Direct Soil
Evaporation
Runoff
on
bare
soil
T, z=Litter
Deposition/
Sublimation
to/from
snowpack
T, z=5 cm
T, z=30 cm
Evaporation
from Open Water
Snowmelt
= 10 cm
Soil Moisture
Flux
Interflow
Moisture z=60 cm
Turbulent Heat Flux to/from
Snowpack/Soil/Plant Canopy
Soil Heat Flux
= 30 cm
= 60 cm
Internal Soil
Moisture Flux
Internal Soil
Heat Flux
∆Snow
∆Moist
= 100 cm
∆Tsoil
Gravitational Flow
Soapgrass
50˚N
40˚N
30˚N
130˚W
70˚W
110˚W
90˚W
We use the 1-D uncoupled Noah Land Surface Model
(LSM; Chen et al., 1996; Ek et al., 2003) with near-surface
atmospheric forcing data for input. This LSM simulates soil
moisture (both liquid and frozen), soil temperature, skin
temperature, snowpack depth, snowpack water equivalent
(and hence snowpack density), canopy water content, and
the energy flux and water flux terms of the surface energy
balance and surface water balance.
Comparisons between the observations (blue) and LSM model results (red)
during the year 2000 at Soapgrass Mountain open site for snow depth, soil
moisture, and soil temperature (top two rows). The bottom row shows the
difference between the model and observations.
Above: Locations of the five sites of paired meteorological stations in the Oregon Cascades.
Moose Mtn.
Right: Photos of four of the five sites showing the contrast between the open and closed canopy locations. The paired sites
are ordered with the open/clear-cut sites on the left and closed
canopy/mature forest sites on the right.
Conclusions
1. The open area sites receive greater solar radiation, precipitation, and have greater soil temperatures than closed canopy
sites.
2. Open sites, such as seen at Soapgrass Mountain, show evidence of regrowth of the forest in reduction of these variables
towards “background” values seen in the mature forest.
Falls Creek
3. The modeling results show generally good fits to the observations at the Soapgrass Mountain open site for the year
2000. However, there are discrepancies with the amount and
timing of snow in the Noah model (e.g. Barlage et al., 2010).
References
Barlage, M., F. Chen, M. Tewari, K. Ikeda, D. Gochis, J. Dudhia, R. Rasmussen, B. Livneh, M. Ek,
and K. Mitchell (2010), Noah land surface model modifications to improve snowpack prediction in
the Colorado Rocky Mountains, J. Geophys. Res., 115, D22101, doi:10.1029/2009JD013470.
Chen, F., K. Mitchell, J. Schaake, Y. Xue, H. Pan, V. Koren, Y. Duan, M. Ek, and A. Betts (1996),
Modeling of land-surface evaporation by four schemes and comparison with FIFE observations, J.
Geophys. Res., 101, 7251-7268.
Ek, M. B., K. E. Mitchell, Y. Lin, E. Rogers, P. Grunmann, V. Koren, G. Gayno, and J. D. Tarpley
(2003), Implementation of Noah land surface model advances in the National Centers for
Environmental Prediction operational mesoscale Eta model, J. Geophys. Res., 108(D22), 8851,
doi:10.1029/2002JD003296.
Acknowledgements
This project was funded through grants EAR-0126029 and EAR-0823516 from the National Science
Foundation.