Proceedings zur 6. Fachtagung BIOMET - Deutsche ...

z – vertical coordinate; Kq, – turbulent-transfer coefficient
for moisture; j=1 inside and j=0 above the canopy
In the prognostic moisture equation, which is relevant for transpiration, the source term (term
with the factor “j” in eq. above) is parameterised by the vegetation parameters leaf area density
(LAD) and stomatal and boundary layer resistance (rs and rb) as well as by the difference
in specific humidity between leaf surface (qw) and ambient air (q).
The plant-specific resistances rs and rb are simulated in HIRVAC using the mechanistic photosynthesis
module PSN6 (FALGE et al., 1996). At present there are PSN6 parameters for
spruce, pine, beech, rape, triticale and grass. The model was tested and compared with measurements
and SVAT models for different observation periods (FALGE et al., 2005).
2.2 New parameterisation of the model
In the new HIRVAC version several parameters of the model PSN6 were scaled by a power
function of soil moisture (matrix potential) to consider the stomatal reaction to a change in
soil water content (according to the stand model STANDFLUX, FALGE et al., 1997):
with Ψ and ΨFC (