Abstract
The soil moisture-based Richards equation is widely used in land models for weather and climate studies, but its numerical solution using the mass-conservative scheme in the Community Land Model is found to be deficient when the water table is within the model domain. Furthermore, these deficiencies cannot be reduced by using a smaller grid spacing. The numerical errors are much smaller when the water table is below the model domain. These deficiencies were overlooked in the past, most likely because of the more dominant influence of the free drainage bottom boundary condition used by many land models. They are fixed here by explicitly subtracting the hydrostatic equilibrium soil moisture distribution from the Richards equation. This equilibrium distribution can be derived at each time step from a constant hydraulic (i.e., capillary plus gravitational) potential above the water table, representing a steady-state solution of the Richards equation. Furthermore, because the free drainage condition has serious deficiencies, a new bottom boundary condition based on the equilibrium soil moisture distribution at each time step is proposed that also provides an effective and direct coupling between groundwater and surface water.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 308-319 |
| Number of pages | 12 |
| Journal | Journal of Hydrometeorology |
| Volume | 10 |
| Issue number | 1 |
| DOIs | |
| State | Published - 2009 |
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ASJC Scopus subject areas
- Atmospheric Science
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Improving the numerical solution of soil moisture-based Richards equation for land models with a deep or shallow water table. / Zeng, Xubin; Decker, Mark.
In: Journal of Hydrometeorology, Vol. 10, No. 1, 2009, p. 308-319.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Improving the numerical solution of soil moisture-based Richards equation for land models with a deep or shallow water table
AU - Zeng, Xubin
AU - Decker, Mark
PY - 2009
Y1 - 2009
N2 - The soil moisture-based Richards equation is widely used in land models for weather and climate studies, but its numerical solution using the mass-conservative scheme in the Community Land Model is found to be deficient when the water table is within the model domain. Furthermore, these deficiencies cannot be reduced by using a smaller grid spacing. The numerical errors are much smaller when the water table is below the model domain. These deficiencies were overlooked in the past, most likely because of the more dominant influence of the free drainage bottom boundary condition used by many land models. They are fixed here by explicitly subtracting the hydrostatic equilibrium soil moisture distribution from the Richards equation. This equilibrium distribution can be derived at each time step from a constant hydraulic (i.e., capillary plus gravitational) potential above the water table, representing a steady-state solution of the Richards equation. Furthermore, because the free drainage condition has serious deficiencies, a new bottom boundary condition based on the equilibrium soil moisture distribution at each time step is proposed that also provides an effective and direct coupling between groundwater and surface water.
AB - The soil moisture-based Richards equation is widely used in land models for weather and climate studies, but its numerical solution using the mass-conservative scheme in the Community Land Model is found to be deficient when the water table is within the model domain. Furthermore, these deficiencies cannot be reduced by using a smaller grid spacing. The numerical errors are much smaller when the water table is below the model domain. These deficiencies were overlooked in the past, most likely because of the more dominant influence of the free drainage bottom boundary condition used by many land models. They are fixed here by explicitly subtracting the hydrostatic equilibrium soil moisture distribution from the Richards equation. This equilibrium distribution can be derived at each time step from a constant hydraulic (i.e., capillary plus gravitational) potential above the water table, representing a steady-state solution of the Richards equation. Furthermore, because the free drainage condition has serious deficiencies, a new bottom boundary condition based on the equilibrium soil moisture distribution at each time step is proposed that also provides an effective and direct coupling between groundwater and surface water.
UR - http://www.scopus.com/inward/record.url?scp=65349171003&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=65349171003&partnerID=8YFLogxK
U2 - 10.1175/2008JHM1011.1
DO - 10.1175/2008JHM1011.1
M3 - Article
AN - SCOPUS:65349171003
VL - 10
SP - 308
EP - 319
JO - Journal of Hydrometeorology
JF - Journal of Hydrometeorology
SN - 1525-755X
IS - 1
ER -