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Predicting evaporation from mountain streams Szeitz, Andras J.
Abstract
Evaporation can be an important control on stream temperature, particularly in the summer when it acts to limit daily maximum stream temperature. Evaporation from streams is usually modelled with the use of a wind function that includes empirically derived coefficients. A small number of studies derived wind functions for individual streams; the fitted parameters varied substantially among sites. In this study, stream evaporation and above-stream meteorological conditions (at 0.5 and 1.5 m above the water surface) were measured at nine mountain streams in southwestern British Columbia, Canada, covering a range of stream widths, temperatures, and riparian vegetation. Evaporation was measured on several days at each stream, at approximately hourly intervals, using nine floating evaporation pans distributed across the channels. The wind function was fit using mixed-effects models to account explicitly for among-stream variability in the parameters. The fixed-effects parameters were tested using leave-one-out cross-validation. The model based on 0.5-m measurements provided improved model performance compared to that based on 1.5-m values, with RMSE of 0.0162 and 0.0187 mm h⁻¹, respectively, relative to a mean evaporation rate of 0.06 mm h⁻¹. Inclusion of atmospheric stability and canopy openness as predictors improved model performance when using the 1.5-m meteorological measurements, with minimal improvement when based on 0.5-m measurements. A laboratory experiment was conducted to test the influences of aeration and flow velocity on evaporation; no significant relationship was observed, but this may be attributable to several methodological issues.
Item Metadata
Title |
Predicting evaporation from mountain streams
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2019
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Description |
Evaporation can be an important control on stream temperature,
particularly in the summer when it acts to limit daily maximum stream
temperature. Evaporation from streams is usually modelled with the use
of a wind function that includes empirically derived coefficients. A
small number of studies derived wind functions for individual streams;
the fitted parameters varied substantially among sites. In this study,
stream evaporation and above-stream meteorological conditions (at 0.5
and 1.5 m above the water surface) were measured at nine mountain
streams in southwestern British Columbia, Canada, covering a range of
stream widths, temperatures, and riparian vegetation. Evaporation was
measured on several days at each stream, at approximately hourly
intervals, using nine floating evaporation pans distributed across the
channels. The wind function was fit using mixed-effects models to
account explicitly for among-stream variability in the parameters. The
fixed-effects parameters were tested using leave-one-out
cross-validation. The model based on 0.5-m measurements provided
improved model performance compared to that based on 1.5-m values, with
RMSE of 0.0162 and 0.0187 mm h⁻¹, respectively, relative to a
mean evaporation rate of 0.06 mm h⁻¹. Inclusion of atmospheric
stability and canopy openness as predictors improved model performance
when using the 1.5-m meteorological measurements, with minimal
improvement when based on 0.5-m measurements. A laboratory experiment
was conducted to test the influences of aeration and flow velocity on
evaporation; no significant relationship was observed, but this may be
attributable to several methodological issues.
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Genre | |
Type | |
Language |
eng
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Date Available |
2019-09-12
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0380868
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2019-11
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International