Urban Soil-Canopy-Atmosphere Exchanges at Submesoscales: Learning from Model Development, Evaluation, and Coupling with LES - Meteorological and Air Quality Models for Urban Areas - page 40

Net radiation Rn Net radiation Rn

Anthropogenic heat
Qanth

Sensible heat
Hsens

Latent heat LE
(evapotranspiration)

Stored heat Gs
(conduction)

(roof) (roof)

(vega) (vega) (vegn) (vegn)

(water) (water)

(pav) (pav)

(bare) (bare) (cova) (cova) (nat) (nat)

Surface layer Surface layer Surface layer Surface layer

Heat transfers Heat transfers

Couchede surf. Couchede surf.

LEpav

Second soil layer Second soil layer

Hsens pav Hsens pav

Qwall
Ts
Twall

Qwall

Precipitations P

Ts
Twall

Tint Tint

Ts pav Ts pav

Evapotranspiration
Etr

Condensation
P'

Evaporation
Ev

Gs pav Gs pav

(vega) (vega)

(roof) (roof)

(vegn) (vegn)

Run off Run off

(bare) (bare) (water) (water)

(pav) (pav)

(cova) (cova)

(nat) (nat)

Surface layer Surface layer Surface layer Surface layer

Semi-impervious Semi-impervious

Infiltration Infiltration

Water transfers Water transfers

Root zone layer Root zone layer

Couchede surf. Couchede surf.

Drainage Drainage

Diffusion Diffusion

Deep soil layer Deep soil layer

Fig. 6.1 Schematic representation of SM2U: the upper box shows the processes modelled in the
energy budget part, with a zoom on the in-street radiation and heat storage processes due to building
walls; the lower box shows the modelled water transfer processes. The black brackets indicate the
different possible tiles within one grid mesh. Precipitation is a model input while the net radiation
is computed by the model from the incoming global and atmospheric radiation inputs (See also
Colour Plate 8 on page 174)

by means of force-restore equations. The heat and water fluxes through the surface
layer are calculated from the surface energy and water balances resulting from the
exchanges with the atmosphere and the underlying soil layer (Fig. 6.1). The advan-
tage of computing in parallel the energy and water transfer processes is threefold: (i)
the partition between sensible and latent heat fluxes is based on the moisture actu-
ally available due to long- and short-term water storage processes, (ii) the heat con-
duction into the ground depends on the actual soil humidity, and (iii) the available
humidity in the canopy layer depends on the actual vegetation evapotranspiration.

6.2 Model Development

The SM2U development consisted of replacing the integrated approach by a tiling
approach. In ISBA the vegetation fraction is an additional layer partially covering
the unique surface soil layer whereas for the tiling approach the surface energy and
water budgets are computed separately for the vegetation and bare soil fractions.
The underlying soil layer under all surface layers and the overlying air layers are
unique. The surface fluxes are averaged for the cell.
The first urbanization development consisted of: