Hydro Thermodynamic Soil Vegetation Scheme

Brief description

In HTSVS (Kramm 1987, Kramm et al. 1994, 1996, Mölders and Kramm 1999), the treatment of the (vertical) heat- and water-transfer processes is based on the Philips-and-de-Vries-type soil physics, i.e., it is based on the principles of the linear thermodynamics of irreversible processes (including the Richards-equation) allowing long-term integration. The exchange of energy and matter between vegetation and atmosphere is parameterized analogous to the resistance networks shown in Figure 1. Vegetation is represented by a single layer. The heterogeneity of the system 'soil-vegetation' on microscale is described by a Deardorff-type mixture-approach, i.e., the effects of bare and plant-covered soil are linearly weighted by the shielding factor associated with the degree to which foliage prevents shortwave radiation from reaching the ground (Fig. 1). Transpiration of water by plants is described by using a Jarvis-type bulk-stomatal resistance approach. Additions are made to HTSVS to accommodate the effects of water extraction by roots and soil wetness on soil albedo (Mölders et al. 1999). Soil albedo now depends on volumetric water content. Moreover, the simple parameterization of infiltration is replaced by an explicit formulation of the Green-and-Ampt-approach (Mölders 1999).

History

HTSVS was developed at University of Frankfurt by Dr. G. Kramm (see, e.g., Kramm and Herbert 1984, Kramm 1987) and further developed for 3D-purposes by Dr. habil. N. Mölders (see, e.g., Mölders 1999) at University of Leipzig. Moreover, HTSVS was enlarged by the inclusion of parameterizations of infiltration and root effects by Dr. habil. N. Mölders (see, e.g., Mölders 1999, Mölders et al. 1999, 2000). In 2000, HTSVS was implemented into MM5 at NCAR by Dr. habil. N. Mölders.

Evaluation

HTSVS is evaluated using GREIV74-, Great PlainsExperiment- (see, e.g., Kramm 1987, 1995, Kramm et al. 1994, 1996), lysimeter- and tensiometer data (see, e.g., Mölders et al. 1999, 2000, 2003) as well as CASES97-data

Options already tested/coupled in MM5

FRAD=1,2,3,4

ICLOUD=1

ICUPA=2,3

IMPHYS=6,7

IBLTYP=5

ISHALLO=0,1

Preliminary results

Within the framework of MM5, HTSVS was run for IOP5 of CASES97

How to run HTSVS

Like OSULSM, but set ISOIL=4. The parameter IGIVLAI allows to chose how the vegetation fraction and leaf area index are dealt with. IGIVLAI=0 shielding factor is pregiven, =1 LAI is pregiven, =2 LAI and shielding factor are taken from DATA statement, =3 2D-field of vegetation fraction is read in and LAI is taken from DATA statement. The parameter ZSLMAX (negative values required) gives the depth of first soil layer (m). ZSLMIN (negative values required) gives the deepest soil layer (m) and TKR=0.5 is a coefficient in the implicit scheme of HTSVS. TKR should be changed for sensitivity studies purposes only.