6.8. jules_hydrology.nml

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

6.8.1. 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.

This controls the range of cfit values tried in calc_fit_fsat.F90 where cfitmax = 0.15 * nfita

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)

Default value is 0 - i.e. surface saturation can occur for any value of water storage. A value of, e.g., 0.5 would indicate that no surface runoff is produced until the soil is 50% saturated.

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 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.