1. Land surface physics in IBIS
based on ‘LSX’ of Pollard and Thompson
designed to be part of an atmospheric model (~hourly timestep)
purpose of land-surface module: calculate energy balance and water balance at the land surface
sensible
heat flux (H)
Visible
precipitation(P) IR
latent heat flux (LE)
Evapotranspiration (E)
surface runoff (RF)
Soil heat flux (G)
sub-surface drainage

2. Each gridcell in IBIS may contain 12 plant functional types (pft)
Representation in the land-surface physics part of the code :
upper canopy
Lower canopy
Each canopy is characterized by 1 set of parameters. (eg:LAI of upper canopy =
sum of lai’s of each tree pft in the grid cell)
Parameters and fluxes depending on the pft are weighted by the relative abundance of the pft in the canopy (e.g : CO2 flux).

3. the temperature of both canopies, of canopy air, of soil, and snow.
Thermal energy and water vapor: done in subroutine turvap and linsolve in file canopy.f
To solve energy balance and water balance, the model needs to calculate
the temperature of both canopies, of canopy air, of soil, and snow.
e.g energy balance of upper canopy (per unit LAI)
the flow of water trough the canopies and through the soil and the humidity and water content of each components Wu
upper canopy
Snow
lower canopy
Soil

4. Energy balance and water balance:
Ta, qa, ua, raina, snowa, Solar radiation za wu z1
Tu,
T12 q12
z12 ws Ts z2 wl
ta : air temperature
tu: temperature of upper canopy leaves
ts: temperature of upper canopy stems
tl: lower canopy temperature
t12: temperature of air within upper canopy
t34: temperature of air within lower canopy
tg: ‘skin’ temperature of soil (temperature of the soil surface)
tsoi(k): temperature of kth soil layer
qa: air specific humidity (g/kg)
q12: specific humidity of air within upper canopy
q34: specific humidity of air within lower canopy
wu: amount of water on upper canopy leaves (intercepted rain/dew)
ws: amount of water on upper canopy stems
wl: amount of water on lower canopy leaves (intercepted rain/dew)
wsoi:
raina : rainfall (mm/s or kg/m2/s)
snowa : snowfall
Solar radiation z3
Snow Tl
T34 q34
z34 z4 Tg
Z=0
Tsoi, wsoi, wisoi
Soil (6 layers)

5. fira Radiation - Infrared
Calculation done in subroutine irrad in file radiation.f Tu Ts
fira
Each ‘medium’ (upper canopy leaves, stems, lower canopy, snow on ground and ground surface) behaves like a black body and emits and absorbs radiation according to :
emissivity * stefan-ct * T4
Fluxes are weighted by the average fractional covers :fu for the upper canopy, fl for the lower canopy, fi for the snow cover
fu*fira
(1-fu)*fira Ti Tl
snow Tg
Soil (6 layers)

6. Radiation - done in subroutines solset, solsur, solalb, solarf, twostr, twoset in file radiation.f
Soil (6 layers)
snow Tu Ts
diffuse Tl Tg
direct
Calculation done separately for visible ( m) and near-infrared ( m)
‘two-stream’ approximation used in each vegetation layer: direct and diffuse beam
Vegetation characterized by transmittance, reflectance and leaf-angle distribution
Soil and snow characterized by albedo
Fluxes are weighted by the fractional covers (shading effect of trees averaged over entire grid cell)

7. Aerodynamics: done in subroutines canini and turcof in file canopy.f
Calculates:
turbulent heat (sensible and latent heat) and water vapor fluxes from soil and canopies to air
transfer coefficients for fluxes between canopy air and air above (e.g: su, a)
Example : upper canopy heat flux:
heat flux between canopy air and free air (Ha)
sensible heat flux between upper
canopy and canopy air (Hu)
T12 Tu Ts
ta : air temperature
tu: temperature of upper canopy leaves
ts: temperature of upper canopy stems
tl: lower canopy temperature
t12: temperature of air within upper canopy
t34: temperature of air within lower canopy
tg: ‘skin’ temperature of soil (temperature of the soil surface)
tsoi(k): temperature of kth soil layer
qa: air specific humidity (g/kg)
q12: specific humidity of air within upper canopy
q34: specific humidity of air within lower canopy
wu: amount of water on upper canopy leaves (intercepted rain/dew)
ws: amount of water on upper canopy stems
wl: amount of water on lower canopy leaves (intercepted rain/dew)
wsoi:
raina : rainfall (mm/s or kg/m2/s)
snowa : snowfall
Solar radiation
Snow Tl
T34 Tg
Soil
Tsoi

8. : wind stress (constant between canopies) : air density
constant-flux layers with logarithmic profile of wind modified by ‘stratification’:
Aerodynamics
elevation ua za
In canopies:
diffusive model
constant flux z1
z12
diffusive
u12
Hyp: Continuity of wind speed and wind stress at canopy boundaries. z2
ta : air temperature
tu: temperature of upper canopy leaves
ts: temperature of upper canopy stems
tl: lower canopy temperature
t12: temperature of air within upper canopy
t34: temperature of air within lower canopy
tg: ‘skin’ temperature of soil (temperature of the soil surface)
tsoi(k): temperature of kth soil layer
qa: air specific humidity (g/kg)
q12: specific humidity of air within upper canopy
q34: specific humidity of air within lower canopy
wu: amount of water on upper canopy leaves (intercepted rain/dew)
ws: amount of water on upper canopy stems
wl: amount of water on lower canopy leaves (intercepted rain/dew)
wsoi:
raina : rainfall (mm/s or kg/m2/s)
snowa : snowfall
Solar radiation
constant flux
: wind stress (constant between canopies)
: air density
Z0: roughness length (height, LAI)
d: displacement height (~height of canopy) z3
z34
u34
diffusive z4
constant flux
Z=0 u4 u3 u2 u1 ua
Wind speed

9. + source : density of soil : thermal conductivity of soil
Soil heat: calculation done in subroutines soilheat, wadjust in file soil.
Each layer characterized by specific heat (csoi), and thermal conductivity (). Both depend on soil texture, and water and ice content.
Solution of :
Heat flux from atmosphere (G)
Ice
water
6 layers
10cm
15cm
50cm
25cm
200cm
100cm
+ source
: density of soil
: thermal conductivity of soil
Source:heat flux from atmosphere (1st layer only), ice freezing in soil
Sinks: ice melt in soil
Averaged for use in
soil biogeochemistry
Tsoi, csoi

10. + source - sinks : volumetric water content : matric potential
Soil water: calculation done in subroutines soilset, soilctl, soilh2o in file soil.f
Water influx (precipitation,
drips from upper and lower canopies,
snowmelt)
Diffusion of water in soil follows Darcy’s law combined with conservation of mass:
Bare soil
evaporation
puddles:
wipud wpud
+ source - sinks
: volumetric water content
: matric potential
: hydraulic conductivity
Source: water flux from puddle (1st layer only)
Sinks: evaporation (1st layer only), water absorbed by roots, drainage (6th layer only)
 and  depend on the volumetric water content and the texture through Clapp and Hornberger’s equations.
In the model the variables are :
wsoi = fraction of soil pore space filled with liquid.
wisoi = fraction of soil pore space filled with ice.
Ice
water
Water pumped
by roots
wisoi, wsoi
drainage

11. Surface of soil: puddles
Water influx (precipitation,
drips from upper and lower canopies,
snowmelt)
evaporation
runoff
Runoff if wpud > wpudmax

12. + source - sinks : density of snow : thermal conductivity of snow
Snow: calculation done in subroutines inisnow (initial.f) , snow, showheat in file snow. F
(person to contact: John Lenters)
Snow characterized by albedo, emissivity, thermal conductivity and density (fixed).
Variables: tsno (temperature for each layer)
hsno (height of each layer)
fi = snow cover fraction in gridcell
(depends on hsno)
Solution of heat equation:
Snowfall + blowing snow from canopies
Heat flux
from air above + rain
sublimation
+ source - sinks
3 layers
: density of snow
: thermal conductivity of snow
Source:heat flux from atmosphere (1st layer only), freezing in soil
Sinks: snow melt
5cm
hsno2 =
hsno3
snowmelt

13. Energy balance: Rn = H + LE + G
Rn = (1-albedo) Visible + IRdown - IRup
Water balance: Precipitation = Evapotranspiration - Runoff - Drainage + W / t
Visible IR
sensible
heat flux (H)
precipitation(P)
latent heat flux (LE)
Evapotranspiration (E)
surface runoff (RF)
Soil heat flux (G)
sub-surface drainage

14. e.g energy balance of upper canopy (per unit LAI)
To solve energy balance and water balance, the model needs to calculate
the temperature of both canopies (Tu, Tl), of canopy air (T12,T34), of soil (Tsoi), and snow(Tsno).
e.g energy balance of upper canopy (per unit LAI) wu Tu
T12 q12 ws Ts
the flow of water trough the canopies and through the soil and the humidity (q12, q34, qg) water (and ice) content of each components (wu, wl, ws, wsoi, wisoi) wl Ti
Snow
Tsno Tl
T34 q34
Tg, qg
Tsoi, wsoi, wisoi
Soil (6 layers)