MOLOCH

1
Soil scheme of MOLOCH
first atmospheric level
fraction of vegetation fVEG
fraction of model box covered by snow fSNOW
air specific humidity above the interface
soil skin temperature
Climatological layer
2
Soil and vegetation properties

• fVEG Fraction of vegetation (seasonal
  function)
• L.A.I. Leaf Area Index (seasonal function)
• ZROOT Root depth (m)
• qWILT, qREF Evapotranspiration range (m3/m3)
• qMIN, qMAX Minimum and maximum water in soil
  (m3/m3)
• ?WKW Coefficient of water diffusivity in soil
  (kg/m2/s)
• ?G Hydric potential (m) at saturation
• b Exponent of hydric potential
• ?GCG Dry soil thermal capacity per unit volume
  (J/m3/oK)
• ? Emissivity (function of water content and
  vegetation)
• ? Albedo (function of water content and
  vegetation)

3
Physical and numerical constants used in the
scheme
Thermal conductivity of snow in Watt/m/oK
Prognostic fields
mass of water (kg/m2) deposited over vegetation
Snow height (m of equivalent water)
Diagnostic fields
Drag coefficient
Turbulent fluxes of heat and specific humidity
(positive upward) and radiation fluxes (positive
downward)
Efficiency of evapotranspiration (depending on
temperature, insolation, and L.A.I.)
4
Saturation of surface air at time t
fraction of model box covered by vegetation and
free of snow
fraction of wet leaf
efficiency of root pumping weighted by the layer
depth
5
Definition of qSKIN at current time t
Air specific humidity over wet leaves
Air specific humidity over bare soil and pools
(ZG is the surface wetness)
coefficient of molecular diffusivity of vapor
into air
6
Atmospheric vertical diffusion
Updated specific humidity at first atmospheric
level
Updated drag coefficient of humidity and
temperature (over land only)
Turbulent flux of specific humidity (kg/m2/s)
positive upward
Turbulent flux of heat (Watt/m2) positive upward
7
Humidity flux disaggregation using the updated
value of q1
Flux over snow in kg/m2/s
Flux over the fraction of wet leaf
Evapotranspiration from the fraction of dry leaf
and from the k-th soil layer (kg/m2/s)
Humidity flux over the fraction of bare soil and
pools (it conserves water exactly).
8
Residual precipitation and WVEG update
Precipitation intercepted by leaves (it can be
negative)
WVEG update
Computation of residual precipitation at the
ground - When the intercepted precipitation is
negative, the (negative) specific humidity flux
increases the residual precipitation (in parole
povere, rugiada che cade a terra)
9
TSKIN soil temperature at the upper interface
from flux balance
Surface heat exchange coefficient ?1
Numerical limitation
thermal diffusivity of ground
(heat flux from the ground)
Newton step
10
Snow height update
1-Fall-Sublimation
(melting parameter)
2-Melting
(Kg/m2/s)
3-Snow fraction update
11
Water flux and content update of the first soil
layer (m3/m3)
Kg/m2/s
Flux correction
12
Water flux and content update of the second soil
layer (m3/m3)
Flux correction
13
Internal heat exchange coefficients
If both ?1 and ?2 are equal to their upper
bounds, T1G at new time step becomes the
arithmetic average between TSKIN and T2G (due to
diffusive terms alone).
14
T1G tendency irreversible mixing and heat
diffusion
heating due to heat exchange with snow at air
temp. T1
heating due to mixing with rain at air temp. T1
Cooling due to melting snow
heat capacity at new time level
heating due to mixing with water diffused from
below (including root pumping)
diffusion of heat
heating due to mixing with melted snow at
freezing temp.
cooling (heating) due to the increase (decrease)
of evaporating water/ice to temperature TSKIN
15
T2G tendency
Final temperature update
Runoff