Modelling evaporation from wetland tundra |
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| Authors: | David A Wessel Wayne R Rouse |
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| Institution: | (1) Department of Geography, McMaster University, L8S 4K1 Hamilton, Ontario, Canada |
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| Abstract: | Evapotranspiration is a major component of both the energy and water balances of wetland tundra environments during the thaw season. Reliable estimates of evapotranspiration are required in the analysis of climatological and hydrological processes occurring within a wetland and in interfacing the surface climate with atmospheric processes. Where direct measurements are unavailable, models designed to accurately predict evapotranspiration for a particular wetland are used.This paper evaluates the performance, sensitivity and limitations of three physically-based, one-dimensional models in the simulation of evaporation from a wetland sedge tundra in the Hudson Bay Lowland near Churchill, Manitoba. The surface of the study site consists of near-saturated peat soil with a sparse sedge canopy and a constantly varying coverage of standing water. Measured evaporation used the Bowen ratio energy balance approach, to which the model results were compared. The comparisons were conducted with hourly and daily simulations.The three models are the Penman-Monteith model, the Shuttleworth-Wallace sparse canopy model and a modified Penman-Monteith model which is weighted for surface area of the evaporation sources.Results from the study suggest that the weighted Penman-Monteith model has the highest potential for use as a predictive tool. In all three cases, the importance of accurately measuring the surface area of each evaporation source is recognized. The difficulty in determining a representative surface resistance for each source and the associated problems in modelling without it are discussed. List of Symbols Models BREB
Bowen ratio energy balance
- P-M
Penman-Monteith combination
- S-W
Shuttleworth-Wallace combination
- W-P-M
Weighted Penman-Monteith combination
Other
AE
Available energy-all surfaces
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AE
c
Available energy-canopy (S-W, W-P-M)
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AE
s
Available energy-bare soil (S-W, W-P-M)
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AE
w
Available energy-open water (W-P-M)
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C
p
Specific heat of air
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D
Vapor pressure deficit
- DAI
Dead area index
- FAI
Foliage area index
- LAI
Leaf area index
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Q
*
Net radiation
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Q
e
Latent heat flux-total
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Q
ec
Latent heat flux-canopy (S-W, W-P-M)
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Q
es
Latent heat flux-bare soil (S-W, W-P-M)
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Q
ew
Latent heat flux-open water (W-P-M)
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Q
g
ground heat flux
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Q
h
Sensible heat flux
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S
Proportion of area in bare soil
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W
Proportion of surface in open water
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r
a
Aerodynamic resistance (P-M, W-P-M)
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r
c
Canopy resistance
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r
s
Generalized optimized surface resistance
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r
st
Stomatal resistance
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r
c
a
Bulk boundary layer resistance (S-W)
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r
s
a
Aerodynamic resistance below mean canopy level (S-W)
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r
s
s
Soil surface resistance (S-W, W-P-M)
Greek 
Bowen ratio
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Psychrometer constant
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Air density
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Slope of saturation vapour pressure vs temperature curve |
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| Keywords: | |
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