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components are contained in two adjacent compartments, the first one is made up of shrubs 
and underlying soil, and the second of open (illuminated) soil. The contribution of each 
component to sensible heat flux will be parameterized. The formulation of effective surface 
temperature and effective surface resistance to heat transfer representing the entire surface 
will be derived by assuming that total sensible heat flux can be approximated as an area 
weighted average of sensible heat flux emanating from each compartment. 
2- MODELING 
Sensible heat flux for a heterogeneous surface can be expressed in terms of effective 
parameters representing the entire surface as : 
where p is the air density (kg/m 2 ), Cp the specific heat of air at constant pressure (J/kg/K), 
and T a is the air temperature at a reference height (°C). T e ff (°C) and r e ff (s/m) are, 
respectively, effective surface temperature, and effective resistance to sensible heat flux 
across the surface-atmosphere interface (snr 1 ). 
described using a classical two-layer model. Sensible heat flux H], emanating from this 
compartment is the sum of the contribution of each of its components, Hj can be writen as: 
Where T e and r e are respectively equivalent temperature and equivalent resistance to heat 
transfer of compartment 1. Following Chehbouni et al. (1993) these 2 parameters are 
expressed as: 
Where Tf and T s f are the temperatures of shrubs and soil under the shrubs respectively, r a f 
and r as are bulk boundary layer and substrate resistances, r a j is aerodynamic resistance of 
the compartment I 
( 1 ) 
The exchange between the atmosphere and the first compartment can be 
Hi - pc P 
Tc~Ta 
( 2 ) 
re 
rafTsf + fasTf 
(3) 
Taf Kas 
rafras 
+ ra\ 
(4) 
raf + ras 
Sensible heat flux Fb, emanating from the second compartment, can be easily formulated 
using a classical one layer model as: 
T, - Tc 
(5)