6.6. jules_hydrology.nml

This file sets the hydrology options. It contains one namelist called JULES_HYDROLOGY.

6.6.1. JULES_HYDROLOGY namelist members

JULES_HYDROLOGY::l_top

Type:logical Default:F

Switch for a TOPMODEL-type model of runoff production.

TRUE

Use a TOPMODEL-type scheme. This is based on Gedney and Cox (2003); see also Clark and Gedney (2008).

FALSE

No TOPMODEL scheme.

See also

References:

• Gedney, N. and P.M.Cox, 2003 , The sensitivity of global climate model simulations to the representation of soil moisture heterogeneity, J. Hydrometeorology, 4, 1265-1275.
• Clark and Gedney, 2008, Representing the effects of subgrid variability of soil moisture on runoff generation in a land surface model, Journal of Geophysical Research - Atmospheres, 113, D10111, doi:10.1029/2007JD008940.

JULES_HYDROLOGY::l_pdm

Type:logical Default:F

Switch for a PDM-type model of runoff production.

PDM is the Probability Distributed Model (Moore, 1985), implemented in JULES following Clark and Gedney (2008).

TRUE

Use a PDM scheme.

FALSE

No PDM scheme.

See also

References:

• Moore, R. J. (1985), The probability-distributed principle and runoff production at point and basin scales, Hydrol. Sci. J., 30, 273-297.
• Clark and Gedney, 2008, Representing the effects of subgrid variability of soil moisture on runoff generation in a land surface model, Journal of Geophysical Research - Atmospheres, 113, D10111, doi:10.1029/2007JD008940.

Only used if l_top = TRUE

JULES_HYDROLOGY::zw_max

Type:real Default:6.0

The maximum allowed depth to the water table (m).

This is the depth to the bottom of an additional layer below the sm_levels soil layers and hence should be set to a value greater than SUM(dzsoil).

JULES_HYDROLOGY::ti_max

Type:real Default:10.0

The maximum possible value of the topographic index.

JULES_HYDROLOGY::ti_wetl

Type:real Default:1.5

A calibration parameter used in the calculation of the wetland fraction.

It is used to increment the “critical” value of the topographic index that is used to calculate the saturated fraction of the gridbox. It excludes locations with large values of the topographic index from the wetland fraction.

See Gedney and Cox (2003).

JULES_HYDROLOGY::nfita

Type:integer Default:20

The number of values tried when fitting wetland and saturation fractions to water table depth in the initialisation.

JULES_HYDROLOGY::l_wetland_unfrozen

Type:logical Default:F

TRUE

Treat the calculations of wetland and surface saturation fractions more like those of an unfrozen soil.

FALSE

Use standard wetland and surface saturation fraction calculations.

Only used if l_pdm = TRUE

JULES_HYDROLOGY::dz_pdm

Type:real Default:1.0

The depth of soil considered by PDM (m).

A value of ~1m can be used.

JULES_HYDROLOGY::b_pdm

Type:real Default:1.0

Shape factor for the pdf.

JULES_HYDROLOGY::s_pdm

Type:real Permitted:0-1 Default:0.0

Minimum soil water content below which there is no surface runoff saturation excess production by PDM (fraction of maximum storage, as S0/Smax)

JULES_HYDROLOGY::l_spdmvar

Type:logical Default:F

Use a linear function of topographic slope to calculate S0/Smax: s_pdm=MAX(0.0,1-(slope/slope_pdm_max)).

The function has been tested for Great Britain catchments.

This function will result in high S0/Smax values for flatter regions and low values for steeper regions.

TRUE

Use a the linear function of slope to calculate S0/Smax.

FALSE

Use a fixed S0/Smax parameter, specified in s_pdm.

Only used if l_spdmvar = TRUE

JULES_HYDROLOGY::slope_pdm_max

Type:real Default:6.0

The maximum topographic slope (deg) in the linear function of slope to calculate S0/Smax. Slopes above this value will result in a S0/Smax value of zero.

A value of 6.0 has been tested for slope fields calculated from a high resolution DEM dataset (50m IHDTM for Great Britain).

For slopes calculated from coarser DEM datasets, a lower value might be more appropriate as fine-resolution features of the terrain are not included.