Land Surface Fields

Land surface fields, or land surface characteristics, are of primary importance in numerical environmental prediction (weather, hydrology). The accuracy of land surface modeling directly depends on the quality of these fields, which provide information on the geometric and thermal characteristics of the surface.

The list of surface fields to be initialized for ISBA (land surface scheme of GEM and GEM-Surf) is the following:

z_0m: total roughness length for momentum turbulent transfers, including orographic, vegetation, and urban components, representative of an area larger than the model grid area (m);
z_{0m_local}: roughness length for momentum turbulent transfers, including only the vegetation and urban (local) components, and representative of the model grid area (m);
veg: total fractional coverage of vegetation over land;
LAI: total leaf area index over vegetation area of the land surface (m2 m-2);
sand: sand fraction of soil (%);
clay: clay fraction of soil (%);
d_rz: root-zone depth (m);
D_d: drainage density (m-1);
R_smin: minimum stomatal resistance (s m-1);
γ_v,R_gl: vegetation parameters for the calculation of the stomatal resistance;
B: form parameter for subgrid-scale surface flow (or runoff);
α_{g_WS}: bare ground broadband white-sky (diffused radiation) snow-free albedo for visible and near-infrared;
α_{g_BS}: bare ground broadband black-sky (direct radiation) snow-free albedo for visible and near-infrared;
α_{veg_WS}: vegetation broadband white-sky (diffused radiation) snow-free albedo for visible and near-infrared;
α_{veg_BS}: vegetation broadband black-sky (direct radiation) snow-free albedo for visible and near-infrared, and;
ε: emissivity of the non-urban land surface.

The general approach that is used to specify most of the surface parameters is schematically presented in the figure below.

surface_fields_org

This methodology is currently being used to produce a consistent set of surface characteristics for regions with urban areas (including buildings and roads) and / or natural areas (including bare soil and vegetation-covered surfaces). In the Surface Processor, the GenPhysX module read the appropriate databases and specify the orographic parameters (grid- and subgrid-scale), the water fractional coverage, the soil texture, and the fractional coverage for each type of vegetation land cover.

The GenPhysX module (Zadra et al., 2008) processes the databases for these specific aspects and perform spatial averaging, counting, as well as calculations for orography (mean height, slope, aspect, and subgrid-scale parameters). Some of the parameters are directly used by GEM and GEM-Surf, such as the soil texture, grid-scale orography, and water fractional coverage. Other GenPhysX outputs are provided to the Surface Pre-Processor (subgrid-scale orographic parameters, vegetation fractions). Together with other inputs, i.e., climatologies for albedo, NDVI, and LAI, the Surface Pre-Processor produces the rest of the surface parameters over land, including the LAI, vegetational fractional coverage, vegetation paramters, albedo, root-zone depth.

The UrbanX module, on the other hand, reads another set of databases to calculate the geometric parameters of city areas and uses a series of look-up tables to specify the thermal parameters for the urban areas. The list of surface parameters to be initialized for TEB (urban component) is the following:

NATF	fraction of natural surface
BLDF	fraction of building
PAVF	fraction of paved area
BLDH	building height
Z0RF	roof aerodynamic roughness length
Z0RD	road aerodynamic roughness length
ALRF	albedo roof
ALRD	albedo road
ALWL	albedo wall
EMRF	emissivity roof
EMRD	emissivity road
EMWL	emissivity wall
HCRF	(ip1=1199) heat capacity layer 1 roof
HCRD	(ip1=1199) heat capacity layer 1 road
HCWL	(ip1=1199) heat capacity layer 1 wall
HCRF	(ip1=1198) heat capacity layer 2 roof
HCRD	(ip1=1198) heat capacity layer 2 road
HCWL	(ip1=1198) heat capacity layer 2 wall
HCRF	(ip1=1197) heat capacity layer 3 roof
HCRD	(ip1=1198) heat capacity layer 3 road
HCWL	(ip1=1197) heat capacity layer 3 wall
TCRF	(ip1=1199) thermal conductivity layer1 roof
TCRD	(ip1=1199) thermal conductivity layer1 road
TCWL	(ip1=1199) thermal conductivity layer1 wall
TCRF	(ip1=1198) thermal conductivity layer2 roof
TCRD	(ip1=1198) thermal conductivity layer2 road
TCWL	(ip1=1198) thermal conductivity layer2 wall
TCRF	(ip1=1197) thermal conductivity layer3 roof
TCRD	(ip1=1197) thermal conductivity layer3 road
TCWL	(ip1=1197) thermal conductivity layer3 wall
DPRF	(ip1=1199) heat capacity layer 1 roof
DPRD	(ip1=1199) heat capacity layer 1 road
DPWL	(ip1=1199) thickness layer 1 wall
DPRF	(ip1=1198) thickness layer 2 roof
DPRD	(ip1=1198) thickness layer 2 road
DPWL	(ip1=1198) thickness layer 2 wall
DPRF	(ip1=1197) thickness layer 3 roof
DPRD	(ip1=1197) thickness layer 3 road
DPWL	(ip1=1197) thickness layer 3 wall
QHTR	sensible anthropogenic heat flux generated by traffic road
QETR	latent anthropogenic heat flux generated by traffic road
QHIN	sensible anthropogenic heat flux generated by industry roof
QEIN	latent anthropogenic heat flux generated by industry roof
WHOR	S_wall/S_horizontal canopy
Z0TW	canopy aerodynamic roughness length canopy

References

For more information on the methods used to generate the surface fields for MCS's operational and research systems, the following documents are available:

Bélair, S., 2012: Algorithms for land surface characteristics in GEM. Internal document. Link to PDF

Bélair, S., 2012: Algorithms for land surface characteristics in the high-resolution external land surface modeling system GEM-Surf. Internal document. Link to PDF

Lemonsu, A., A. Leroux, S. Bélair, S. Trudel, and J. Mailhot, 2008: A general methodology of urban land cover type classification for atmospheric modeling. Internal document. Link to PDF

Leroux, A., J.-P. Gauthier, A. Lemonsu, S. Bélair, and J. Mailhot, 2009: Automated urban land used and land cover classification for mesoscale atmospheric modeling over Canadian cities. Geomatica, 63, 393-406. Link to PDF

Zadra, A., J.-P. Gauthier, and A. Leroux, 2008: GenPhysX a user's guide to input/output and methods. Internal document. Link to PDF