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4.3.12. Grass

Properties for grass and lawn surfaces.

Grass surfaces include managed lawns, parks, and playing fields. They provide cooling through evapotranspiration and have moderate albedo values. Irrigation and maintenance significantly affect their water use and energy balance.

Parameters:

sfr

Surface fraction of grid area covered by this surface type

Unit:

dimensionless

Example:

0.14285714285714285

emis

Surface emissivity for longwave radiation

Unit:

dimensionless

Example:

0.95

ohm_threshsw

Summer/winter threshold based on temperature for OHM calculation

Unit:

degC

Example:

0.0

ohm_threshwd

Soil moisture threshold determining whether wet/dry OHM coefficients are applied

Unit:

dimensionless

Example:

0.0

ohm_coef

The ohm_coef parameter group is defined by the Seasonal/Wetness OHM Coefficients structure.

soildepth

Depth of soil layer below surface for hydrological calculations, controlling sub-surface water storage and drainage processes. Site-specific value typically determined from soil surveys or borehole data

Unit:

mm

Default:

None (optional)

soilstorecap

Maximum water storage capacity of soil layer, representing total water holding capacity between field capacity and wilting point. Site-specific value dependent on soil texture, structure, and depth

Unit:

mm

Default:

None (optional)

statelimit

Minimum water storage capacity for state change

Unit:

mm

Example:

10.0

wetthresh

Surface wetness threshold for OHM calculations

Unit:

dimensionless

Example:

0.5

sathydraulicconduct

Saturated hydraulic conductivity of soil layer, controlling water drainage rate through fully saturated soil. Site-specific value determined from soil texture (higher for sandy, lower for clay); typically measured via laboratory or field infiltration tests

Unit:

mm s^-1

Default:

None (optional)

soildensity

Bulk soil density

Unit:

g cm^-3

Default:

None (optional)

waterdist

Water distribution for grass

The waterdist parameter group is defined by the Water Distribution structure.

storedrainprm

Storage and drain parameters

The storedrainprm parameter group is defined by the Drainage Parameters structure.

snowpacklimit

Limit of snow that can be held on surface

Unit:

mm

Example:

10.0

thermal_layers

Thermal layers for the surface

The thermal_layers parameter group is defined by the Thermal Layers structure.

irrfrac

Fraction of surface area that can be irrigated

Unit:

dimensionless

Example:

0.0

ref

The ref parameter group is defined by the Reference Info structure.

alb_min

Minimum albedo (trees: leaf-off; grass: full-leaf)

Unit:

dimensionless

Example:

0.2

alb_max

Maximum albedo (trees: leaf-on; grass: sparse or senesced)

Unit:

dimensionless

Example:

0.3

beta_bioco2

Light-saturated gross photosynthesis rate of the canopy

Unit:

umol m^-2 s^-1

Default:

None (optional)

beta_enh_bioco2

Enhanced photosynthesis coefficient related to vegetation fraction

Unit:

umol m^-2 s^-1

Example:

0.7

alpha_bioco2

Mean apparent ecosystem quantum yield (initial slope of light-response curve)

Unit:

umol CO2 umol photons^-1

Default:

None (optional)

alpha_enh_bioco2

Enhanced quantum yield coefficient related to vegetation fraction

Unit:

umol CO2 umol photons^-1

Example:

0.9

resp_a

Base respiration rate coefficient

Unit:

umol m^-2 s^-1

Default:

None (optional)

resp_b

Respiration temperature sensitivity coefficient

Unit:

K^-1

Default:

None (optional)

theta_bioco2

Curvature parameter for non-rectangular hyperbola at light saturation

Unit:

dimensionless

Default:

None (optional)

maxconductance

Maximum surface conductance

Unit:

mm s^-1

Example:

0.5

min_res_bioco2

Minimum soil respiration rate for cold-temperature limit

Unit:

umol m^-2 s^-1

Example:

0.1

lai

Leaf area index parameters

The lai parameter group is defined by the LAI structure.

ie_a

Irrigation efficiency coefficient-automatic

Unit:

dimensionless

Example:

0.5

ie_m

Irrigation efficiency coefficient-manual

Unit:

dimensionless

Example:

0.6