Modelling vegetation heterogeneity effects on terrestrial water and energy balances

A model of terrestrial water and energy balances is applied to a catchment with heterogeneous vegetation cover. The model couples the surface energy balance with the soil and surface water balance. The catchment is modelled as a nest of one-dimensional models (on a scale of ∼1 km²). The scheme allows for a known distribution of patches of different, but known, characteristics which can be integrated to give a total areal response to atmospheric boundary layer conditions. The Conjurunup catchment, in the south-west region of Western Australia, has a patchwork surface of vegetation and soil moisture conditions resulting from a combination of forestry and mining practices. Model results suggest that satellite measurements of surface temperatures can be used to estimate daily sensible heat flux from the surface in summer, but not in winter. The seasonality of this relationship is due to the soil moisture control of surface energy balance in summer. A linear relationship can be defined between the surface-air temperature difference and daily total sensible heat flux with the coefficients dependent on surface conditions, in particular leaf area index. Yearly total rainfall was also important, reflecting soil moisture levels.