6.6. jules_soil.nml

This file sets the soil options and parameters. It contains one namelist called JULES_SOIL.

6.6.1. JULES_SOIL namelist members

JULES_SOIL::sm_levels

Type:integer Permitted:>= 1 Default:4

Number of soil layers.

A value of 4 is often used, and the soil layer depths in the examples have been tuned using this.

Warning

If ncpft > 0, sm_levels >= 3 is required.

JULES_SOIL::l_vg_soil

Type:logical Default:F

Switch for van Genuchten soil hydraulic model.

TRUE

Use van Genuchten model.

FALSE

Use Brooks and Corey model [*].

See also

References:

• Brooks, R.H. and A.T. Corey, 1964, Hydraulic properties of porous media. Colorado State University Hydrology Papers 3.
• van Genuchten, M.T., 1980, A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils. Soil Science Society of America Journal, 44:892-898.

JULES_SOIL::l_dpsids_dsdz

Type:logical Default:F

Switch to calculate vertical gradient of soil suction with the assumption of linearity only for fractional saturation (consistent with the calculation of hydraulic conductivity).

JULES_SOIL::l_soil_sat_down

Type:logical Default:F

Switch for dealing with supersaturated soil layers. If a soil layer becomes supersaturated, the water in excess of saturation will be put into the layer below or above according to this switch.

TRUE

Any excess is put into the layer below. Any excess from the bottom layer becomes subsurface runoff.

FALSE

Any excess is put into the layer above. Any excess from the top layer becomes surface runoff. This option was used in JULES2.0.

JULES_SOIL::soilhc_method

Type:integer Permitted:1, 2 or 3 Default:1

Switch for soil thermal conductivity model.

1. Use approach of Cox et al (1999), as in JULES2.0.

   This is likely to predict values of soil thermal conductivity that are too low (Dharssi et al, 2009).
2. Use approach of Dharssi et al (2009), which was adapted from Johansen (1975) and described by Peters-Lidard et al. (1998).

   This is not recommended for organic soils.
3. Use approach of Chadburn et al (2015).

   This is recommended when using organic soils, which can have a much lower saturated thermal conductivity than mineral soils.

See also

References:

• Chadburn et al (2015). An improved representation of physical permafrost dynamics in a global land-surface scheme. Geoscientific Model Development
• Dharssi et al (2009). New soil physical properties implemented in the Unified Model at PS18. Met Office Technical note 528
• Johansen (1975). Thermal conductivity of soils. PhD thesis. University of Trondheim, Norway
• Peters-Lidard et al (1998). The effect of soil thermal conductivity parameterisation on surface energy fluxes and temperatures. J. Atmos. Sci. 55:1209-1224

JULES_SOIL::l_bedrock

Type:logical Default:F

Switch for using a thermal bedrock column beneath the soil column. The bedrock has no hydrological processes - diffusion of heat is the only process represented.

Properties of the bedrock can be set using ns_deep, hcapdeep, hcondeep and dzdeep.

TRUE

An additional bedrock column is used below the soil column.

FALSE

No effect.

See also

For full details see Chadburn et al. (2015)

Bedrock parameters (only used if l_bedrock = TRUE)

JULES_SOIL::ns_deep

Type:integer Permitted:>= 1 Default:100

The number of levels in the thermal-only bedrock.

JULES_SOIL::hcapdeep

Type:real Default:2100000.0

The heat capacity of the bedrock (J K^-1 m^-3 ).

JULES_SOIL::hcondeep

Type:real Default:8.6

The heat conductivity of the bedrock (W m^-2 K^-1 ).

JULES_SOIL::dzdeep

Type:real Default:0.5

The thickness of the bedrock layers (m).

JULES_SOIL::cs_min

Type:real Default:1.0e-6

Minimum allowed soil carbon (kg m^-2).

JULES_SOIL::zsmc

Type:real Permitted:> 0 Default:1.0

If a depth-averaged soil moisture diagnostic is requested, the average is calculated from the surface to this depth (m).

JULES_SOIL::zst

Type:real Permitted:> 0 Default:1.0

If a depth-averaged soil temperature diagnostic is requested, the average is calculated from the surface to this depth (m).

JULES_SOIL::confrac

Type:real Permitted:0 <= confrac <= 1 Default:0.3

The fraction of the gridbox assumed to be covered by convective precipitation.

JULES_SOIL::dzsoil_io

Type:real(sm_levels) Default:None

The soil layer depths (m), starting with the uppermost layer.

Note that the soil layer depths (and hence the total soil depth) are constant across the domain.

In all the examples, JULES uses layer depths of 0.1, 0.25, 0.65 and 2.0m, giving a total depth of 3.0m. It is recommended that this is used unless there is good reason not to.

Footnotes

[*]

In the JULES2.0 User Manual this was described as the ‘Clapp and Hornberger’ model and the JULES code still refers to ‘Clapp and Hornberger’ rather than ‘Brooks and Corey’. In fact there are important differences between these two hydraulic models (Toby Marthews, pers comm.). There has been confusion in the literature and in past documentation of MOSES/JULES, resulting in these differences often being ignored, but JULES uses the Brooks and Corey model. Hopefully this confusion will be removed from future releases. Reference: Clapp, R.B. and G.M.Hornberger, 1978, Empirical Equations for Some Soil Hydraulic Properties. Water Resources Research 14:601-604.