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| Titel |
A non-equilibrium model for soil heating and moisture transport during extreme surface heating: the soil (heat–moisture–vapor) HMV-Model Version 1 |
| VerfasserIn |
W. J. Massman |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 11 ; Nr. 8, no. 11 (2015-11-06), S.3659-3680 |
| Datensatznummer |
250116663
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| Publikation (Nr.) |
 copernicus.org/gmd-8-3659-2015.pdf |
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| Zusammenfassung |
| Increased use of prescribed fire by land managers and the increasing
likelihood of wildfires due to climate change require an improved modeling
capability of extreme heating of soils during fires. This issue is addressed here by developing and testing the soil (heat–moisture–vapor) HMV-model, a 1-D
(one-dimensional) non-equilibrium (liquid–vapor phase change) model of soil
evaporation that simulates the coupled simultaneous transport of heat, soil
moisture, and water vapor. This model is intended for use with surface
forcing ranging from daily solar cycles to extreme conditions encountered
during fires. It employs a linearized Crank–Nicolson scheme for the
conservation equations of energy and mass and its performance is evaluated
against dynamic soil temperature and moisture observations, which were
obtained during laboratory experiments on soil samples exposed to surface
heat fluxes ranging between 10 000 and 50 000 W m−2. The
Hertz–Knudsen equation is the basis for constructing the model's
non-equilibrium evaporative source term. Some unusual aspects of the model
that were found to be extremely important to the model's performance include
(1) a dynamic (temperature and moisture potential dependent) condensation
coefficient associated with the evaporative source term, (2) an infrared
radiation component to the soil's thermal conductivity, and (3) a dynamic
residual soil moisture. This last term, which is parameterized as a function
of temperature and soil water potential, is incorporated into the water
retention curve and hydraulic conductivity functions in order to improve the
model's ability to capture the evaporative dynamics of the strongly bound
soil moisture, which requires temperatures well beyond
150 °C to fully evaporate.
The model also includes film flow, although this phenomenon did not
contribute much to the model's overall performance. In general, the model
simulates the laboratory-observed temperature dynamics quite well, but is
less precise (but still good) at capturing the moisture dynamics. The model
emulates the observed increase in soil moisture ahead of the drying front and
the hiatus in the soil temperature rise during the strongly evaporative stage
of drying. It also captures the observed rapid evaporation of soil moisture
that occurs at relatively low temperatures (50–90 °C), and can
provide quite accurate predictions of the total amount of soil moisture
evaporated during the laboratory experiments. The model's solution for water
vapor density (and vapor pressure), which can exceed 1 standard atmosphere,
cannot be experimentally verified, but they are supported by results from
(earlier and very different) models developed for somewhat different purposes
and for different porous media. Overall, this non-equilibrium model provides
a much more physically realistic simulation over a previous equilibrium model
developed for the same purpose. Current model performance strongly suggests
that it is now ready for testing under field conditions. |
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