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Land Surface Models for Climate Models: Description and Application
Advanced Study Program Summer ColloquiumNational Center for Atmospheric ResearchBoulder, COJune 2006
Gordon BonanNational Center for Atmospheric ResearchBoulder, Colorado
•
Provides the boundary conditions at the land-atmosphere interface–
e.g. albedo, surface temperature, surface fluxes•
Partitions available energy at the surface into sensible and latent heat flux components•
Partitions rainfall into runoff and evaporation–
Evaporation provides surface-atmosphere moisture flux–
River runoff provides freshwater input to the oceans•
Provides the carbon fluxes at the surface (photosynthesis, respiration)•
Updates state variables which affect surface fluxes–
e.g. snow cover, soil moisture, soil temperature, vegetation cover, leaf area index
•
LSM cost is actually not that high ( ~10% of full coupled model)
Role of land surface models in GCMs
Role of land surface models in GCMsThe land-surface model solves (at each timestep)
–
Surface energy balance
(and other energy balances, e.g. in canopy, snow, soil)•
S↓
+ L↓
= S↑
+ L↑
+ λE + H + G –
S↓, S↑
are down(up)welling solar radiation –
L↓
, L↑
are down(up)welling longwave radiation–
λ
is latent heat of vaporization, E is evaporation–
H is sensible heat flux–
G is ground heat flux
–
Surface water balance
(and other water balances such as snow and soil water)•
P = ES
+ ET
+ EC
+ RSurf
+ RSub-Surf
+ ∆SM / ∆t–
P is rainfall–
ES
is soil evaporation, ET
is transpiration, EC
is canopy evaporation–
RSurf
is surface runoff, RSub-Surf
is sub-surface runoff–
∆SM / ∆t is the change in soil moisture over a timestep
–
Carbon balance
(and plant and soil carbon pools)•
NPP = GPP –
Ra = (∆Cf
+ ∆Cs
+ ∆Cr
) / ∆t•
NEP = NPP –
Rh •
NBP = NEP -
Combustion–
NPP is net primary production, GPP is gross primary production–
Ra is autotrophic (plant) respiration, Rh is heterotrophic (soil) respiration–
∆Cf
, ∆Cs
, ∆Cr
are foliage, stem, and root carbon pools–
NEP is net ecosystem production, NBP is net biome production–
Combustion is carbon loss during fire
Surface energy balance
(S↓-S↑) + εL↓
= L↑[Ts
] + H[Ts
] + λE[Ts
] + G[Ts
]
With atmospheric forcing and surface properties specified, solve
for temperature Ts
that balances the energy budget
Surface energy balance and surface temperature
Atmospheric forcingS↓
-
incoming solar radiationL↓
-
incoming longwave radiationTa
–
air temperatureea
– vapor pressure
Surface propertiesS↑
-
reflected solar radiation (albedo)ε
-
emissivityraH
–
aerodynamic resistance (roughness length)raW
–
aerodynamic resistance (roughness length)Tsoil
–
soil temperaturek –
thermal conductivityΔz –
soil depth
4 (1( 273.15) )sL T Lεσ ε+ −↑= + ↓
( )a sp
aH
T TH Cr
ρ −= −
( )*[ ]a sp
aW
e e TCE
rρ
λγ
−= −
( )s soilT TG k
z−
=Δ
0
2
4
6
8
10
12
14
16
1 2 3 4 5 6 7 8 9 10
Wind speed ( m s-1)
Hei
ght a
bove
gro
und
(m)
Day 14
Day 12
Day 35
Similar logarithmic profiles for temperature and vapor pressure
Logarithmic wind profile in atmosphere near surface
Turbulent fluxes
( )/ / 1/*z u u z k∂ ∂ = ( ) ( )2 1 2 1/ ln /*u u u k z z− = ( ) ( )0( ) / ln /* Mu z u k z z=
( ) ( ) 0( ) / ln /* Mu z u k z d z⎡ ⎤= −⎣ ⎦
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Turbulent fluxes
z0M
z0H
z
raM raM
r*b
Wind speed Temperature
Hei
ght
raH = raM + r*b
θsθzuzus = 0
2
2 0
2 0 0
2 0 0
1 ln ( )
1 ln ( ) ln ( )
1 ln ( ) ln ( )
maM M
m haH M H
m waW M W
z dr zk u
z d z dr z zk u
z d z dr z zk u
ψ ζ
ψ ζ ψ ζ
ψ ζ ψ ζ
⎡ ⎤⎛ ⎞⎢ ⎥⎜ ⎟⎢ ⎥⎜ ⎟⎝ ⎠⎣ ⎦
⎡ ⎤ ⎡ ⎤⎛ ⎞ ⎛ ⎞⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦
⎡ ⎤ ⎡ ⎤⎛ ⎞ ⎛ ⎞⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦
−= −
− −= − −
− −= − −
( )a sp
aH
TH Cr
θρ −= −
( ) / /s aM aMu u r u rτ ρ ρ= − =
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Canopy Water
Snow
Hydrology
Drainage
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface RunoffEvaporation
Transpiration
Precipitation
Soil Water
Redistribution
Direct Solar
Radiation
Absorbed SolarRadiation
Diff
use
Sol
ar
Rad
iatio
n
Long
wav
e R
adia
tion
Reflected Solar Radiation
Em
itted
Lon
g-w
ave
Rad
iatio
n
Sen
sibl
e H
eat F
lux
Late
nt H
eat F
lux
ua0
Momentum FluxWind Speed
Soil Heat Flux
Heat Transfer
Pho
tosy
nthe
sis
Biogeophysics
Community Land Model
Community Land Model
• Land model for Community Climate System Model•
Developed by the CCSM Land Model Working Group in partnership with university and government laboratory collaborators
Energy fluxes: radiative transfer; turbulent fluxes (sensible, latent heat); heat storage in soil; snow melt
Hydrologic cycle: interception of water by leaves; infiltration and runoff; snow accumulation and melt; multi-layer soil water; partitioning of latent heat into evaporation of intercepted water, soil evaporation, and transpiration
Hydrometeorology
Bonan et al. (2002) J Climate 15:3123-3149Oleson
et al. (2004) NCAR/TN-461+STRDickinson et al. (2006) J Climate 19:2302-2324
Community Land Model
Vegetation dynamics
0
0.3
-10 25 60Temperature (°C)
μgC
O2⋅
g-1⋅s
-1 Root
HeterotrophicRespiration
Ecosystem carbon balance
Growth Respiration
μgC
O2⋅
g-1⋅s
-1
0 1 2Foliage
Nitrogen (%)
0 15 30Temperature
(°C)
μgC
O2⋅
g-1⋅s
-1
0 500 1000Ambient
CO2 (ppm)
Photosynthesis
0 -1 -2
Foliage Water Potential (MPa)
μgC
O2⋅
g-1⋅s
-1
0 15003000Vapor Pressure
Deficit (Pa)
46
20
0 500 1000PPFD
(μmol⋅m-2⋅s-1)
46
20
46
20
Sapwood
0
0.01
-10 25 60Temperature (°C)
μgC
O2⋅
g-1⋅s
-1Foliage
0
0.5
-10 25 60Temperature (°C)
μgC
O2⋅
g-1⋅s
-1
0 15 30Temperature
(°C)
Rel
ativ
e R
ate
1
8
Soil Water (% saturation)
Rel
ativ
e R
ate
0 1000
1
AutotrophicRespiration
Litterfall
NutrientUptake
Dynamic vegetation
Leaf phenology
Needleleaf evergreen treeBroadleaf deciduous tree
1
2
3
4
5
6
0
Leaf
Are
a In
dex
Jan
Feb
Mar Ap
rM
ay Jun
Jul
Aug
Sep
Oct Nov
Dec
Bonan et al. (2003) Global Change Biology 9:1543-1566Levis et al. (2004) NCAR/TN-459+IABonan
& Levis (2006) J Climate 19:2290-2301
Water depth, w
Critical depth, w0
Runoff
Precipitation Evaporation
Sensible heat
Ta
Ts
Latent heat
ra
ea
e* (Ts )
ra /β
E = β
Epβ
= 1 for w≥w0β
= w/w0 for w<w0
First-generation models
Simple energy balance model: (1-r)S↓
+ εL↓
= L↑[Ts
] + H[Ts
] + λE[Ts
]Prescribed surface albedoBulk parameterizations of sensible and latent heat fluxNo influence of vegetation on surface fluxesPrescribed soil wetness factor β
or calculated wetness from bucket modelNo soil heat storage
Manabe
(1969) Monthly Weather Review 97:739-774Williamson et al. (1987) NCAR/TN-285+STR
( )a sp
a
T TH C
rρ
−= −
( )*[ ]/
p a s
a
C e e TE
rρ
λγ β
−= −
Shukla
& Mintz
(1982) Science 215:1498-1501
Green world vs
desert worldTwo climate model experimentsWet –
evapotranspiration not limited by soil water; vegetated planetDry –
no evapotranspiration; desert planet
July surface temperature (°C)
Wet soil
Dry soil
July precipitation (mm/day)
Wet soil
Dry soil
Dry soil warmer than wet soil Dry soil has less precipitation
Second-generation models
Vegetation and hydrologic cycle
Dickinson et al. (1986) NCAR/TN-275+STR Sellers et al. (1986) J Atmos
Sci
43:505-531
Biosphere-Atmosphere Transfer Scheme (BATS) Simple Biosphere Model (SiB)
Radiative transfer
0.00.10.20.30.40.50.60.70.80.91.0
0 1 2 3 4 5 6Leaf Area Index (m2 m-2)
Frac
tiona
l Can
opy
Abso
rptio
n
Visible
Near-infrared
0.00.10.20.30.40.50.60.70.80.91.0
0 1 2 3 4 5 6Leaf Area Index (m2⋅m-2)
Can
opy
Albe
do
Near-infrared
Visible
Snow-Covered Ground
Random leaf orientationZenith angle = 45°
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5 6 7 8Leaf Area Index
Sun
lit L
eaf A
rea
Inde
x
Zenith Angle = 30°
randomhorizontalvertical
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Sensible Heat
Bare SurfaceNo Vegetation
Bulk SurfaceWith Vegetation
One VegetationLayer
Two VegetationLayers
Ta Ta Ta
Ts Tg
Tv
Tg
Tvu
Tvl
ea ea ea
es eg eg
ev
evu
evl
Latent Heat
Bulk SurfaceNo Vegetation
Bulk SurfaceWith Vegetation
One VegetationLayer
Two VegetationLayers
raH
raW
raH
Ta
Ts
raH
rs
rac
raH
racu
racl
rcu
rcl
raW
rac
rc
rc
rcu
rcl
raW
racu
racl
Tac
Tacu
Tacl
eac
eacu
eacl
ea
es
raW
rs
rs
Plant canopy
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
PhotosyntheticallyActive Radiation
Guard CellGuard Cell
CO2 H2 O
Moist Air
Dry Air
CO2 + 2 H2 O → CH2 O + O2 + H2 Olight
ChloroplastLow CO2
High CO2
Stomatal Gas Exchange
Stomata Open: • High Light Levels• Moist Leaf• Warm Temperature• Moist Air• Moderate CO2• High Leaf Nitrogen
Leaf Cuticle
Stomata Close (Smaller Pore Opening): • Low Light Levels• Dry Leaf• Cold Temperature• Dry Air• High CO2• Low Leaf Nitrogen
Leaf stomatal resistance
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
PhotosyntheticallyActive Radiation
Guard CellGuard Cell
CO2 H2 O
Moist Air
Dry Air
CO2 + 2 H2 O → CH2 O + O2 + H2 Olight
ChloroplastLow CO2
High CO2
Leaf Cuticle
Boundary Layer Thickness: 1 to 10 mm H
eigh
t
TemperatureLow High
Wind SpeedHigh0
rs
rbrb
Sensible Heat
Leaf boundary layer
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Plant canopy
Ts
Ta
rb /2
rb /2
ei =e*(Ts )rbrs
eaes (rs +rb )
ci
1.37rb1.65rs
cacs
Latent Heat
Photosynthesis
Sensible Heat
StomataLeaf
BoundaryLayer
(1.65rs +1.37rb )
Total Resistance
Ts
Tac Ta
rb /(2L) ra
rb /(2L)+ra
ei =e*(Ts )rb /L rars /L
eac eaes (rs +rb )/L+ra
ci
1.37rb /L1.65rs /L
cacs
Latent Heat
Photosynthesis
Sensible Heat
Canopy Atmosphere
Surface Layer
(1.65rs +1.37rb )/L
Total Resistance
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Soil temperature
Δy
Δz
Δx
F k Tz
k Tz
= − FHIK = −
∂∂FHIK
ΔΔ
Fin
Fout
change in storage = flux in - flux out
ρ⋅ FHGIKJ ⋅ ⋅ ⋅ = − − ⋅ ⋅c T
tx y z F F x yΔ
ΔΔ Δ Δ Δ Δ( )in out
ρ ⋅ FHGIKJ = −FHGIKJc T
tFz
ΔΔ
ΔΔ
ρ ⋅ ∂∂FHGIKJ =
∂∂
⋅∂∂
FHGIKJ =
∂
∂
FHGIKJ
c Tt z
k Tz
k T
z
2
2
Vertical Heat Transfer
5 mmA 41°C
15 mmB 37°C
F
F
= −⋅
⋅−F
HGIKJ
= −
1 5 41 370 01
600
..
W
m o C
o C o C m
W / m 2
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Hydrologic cycle
Canopy Water
Snow
Hydrology
Drainage
Evaporation
Interception
Melt
Sublimation
ThroughfallStemflow
Infiltration Surface RunoffEvaporation
Transpiration
Precipitation
Soil Water
Redistribution
Direct Solar
Radiation
Absorbed SolarRadiation
Diff
use
Sol
ar
Rad
iatio
n
Long
wav
e R
adia
tion
Reflected Solar Radiation
Em
itted
Lon
g-w
ave
Rad
iatio
n
Sen
sibl
e H
eat F
lux
Late
nt H
eat F
lux
ua0
Momentum FluxWind Speed
Soil Heat Flux
Heat Transfer
Pho
tosy
nthe
sis
Biogeophysics
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Soil water –
Richards equation
Δy
Δz
Δx
F k zz
kz
F k zz
kz
kz
= −+L
NMOQP = − +FH
IK
= −∂ +
∂LNM
OQP = −
∂∂
+FHIK = −
∂∂
⋅∂∂
+FH
IK
ΔΔ
ΔΔ
( )
( )
ψ ψ
ψ ψ θ ψθ
1
1 1Fin
Fout
change in storage = flux in - flux out
ΔΔ
Δ Δ Δ Δ Δθt
x y z F F x yFHGIKJ ⋅ ⋅ ⋅ = − − ⋅ ⋅( )in out
∂∂
=∂∂
∂∂
⋅∂∂
FHG
IKJ +
LNM
OQP
θ θ ψθt z
kz
1
Δ Δ Δ Δθ / /t F z= −
Vertical Water Flow
50 mmA
550 mmB
F
F
= − ⋅− + − − +LNM
OQP
= −
2 478 500 843 mm 0500
3 46
mmhr
mm mm mm mm
mm / hr
( ) ( )
.
ψ=-478 mmz=500 mm
ψ=-843 mmz=0 mm
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Charney
(1975) QJRMS 101:193-202Charney
et al. (1975) Science 187:434-435
Land degradation
Dead vegetation in drought-stricken area, Sol-Dior area, Senegal (FAO, Ch. Errath)
Goat seeks food in the sparsely vegetated Sahel of Africa (US AID)
Climate feedbackOvergrazing
Less Rainfall
Decreased CloudsAnd Convection
Subsidence
Decreased Net Radiation
Surface Cooling
Increased Albedo
Drought
Reduced Vegetation
Cover
Degradation scenario -
the vegetation type within the shaded area was changed to type 9 to represent
degradation: less vegetation, lower LAI, smaller surface roughness length, higher albedo, sandy soil
Broadleaf evergreen tree
Broadleaf tree/ground cover
Broadleaf shrub/ground cover
Broadleaf shrub/bare soil
Climate model experiments
Clark et al. (2001) J Climate 14:1809-1822
Land degradation
July-August-September precipitation differences
(mm/day) due to degradation. Differences that are significant at the 95% confidence level are shaded and the degraded area is enclosed by a solid line.
Clark et al. (2001) J Climate 14:1809-1822
Climate impacts
July-August-September mean differences due to degradation. Values are means over the degraded area. D–C is the difference between degraded and control values.
Land degradation
(NASA/GSFC/LaRC/JPL)
Settlement and deforestation surrounding Rio Branco, Brazil (10°S, 68°W) in the Brazilian state of Acre, near the border with Bolivia. The large image covers an area of 333 km x 333 km.
Tropical deforestation
(National Geographic Society)
Surface Change Climate Change
Study Δalbedo Δz0 ΔT
(°C)
ΔP
(mm)
ΔET
(mm)
Dickinson and Henderson-Sellers (1988) + - +3.0 0 -200
Lean and Warrilow (1989) + - +2.4 -490 -310
Nobre et al. (1991) + - +2.5 -643 -496
Dickinson and Kennedy (1992) + - +0.6 -511 -256
Mylne and Rowntree (1992) + unchanged -0.1 -335 -176
Henderson-Sellers et al. (1993) + - +0.6 -588 -232
Lean and Rowntree (1993) + - +2.1 -296 -201
Pitman et al. (1993) + - +0.7 -603 -207
Polcher and Laval (1994a) + unchanged +3.8 +394 -985
Polcher and Laval (1994b) + - -0.1 -186 -128
Sud et al. (1996) + - +2.0 -540 -445
McGuffie et al. (1995) + - +0.3 -437 -231
Lean and Rowntree (1997) + - +2.3 -157 -296
Hahmann and Dickinson (1997) + - +1.0 -363 -149
Costa and Foley (2000) + - +1.4 -266 -223
Annual response to Amazonian deforestation in various climate model studies. Δalbedo and Δz0
indicate the change in surface albedo and roughness due to deforestation (+, increase; -, decrease). ΔT, ΔP, and ΔET are the simulated changes in temperature, precipitation, and evapotranspiration. Shading denotes warmer, drier climate.
Warmer, drier tropical climate
Tropical deforestation
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Bonan (1995) JGR 100:2817-2831Denning et al. (1995) Nature 376:240-242Denning et al. (1996) Tellus
48B:521-542, 543-567
Stomatal Gas Exchange
Third-generation models
PhotosyntheticallyActive Radiation
Guard CellGuard Cell
CO2 H2 O
Moist Air
CO2 + 2 H2 O → CH2 O + O2 + H2 Olight
ChloroplastLow CO2
Stomata Open: • High Light Levels• Moist Leaf• Warm Temperature• Moist Air• Moderate CO2• High Leaf Nitrogen
Leaf Cuticle
-1012345678
0 200 400 600 800 1000 1200 1400Photosynthetic Photon Flux Density (μmol⋅m-2⋅s-1)
Net
Pho
tosy
nthe
sis
(μm
ol⋅m
-2⋅s
-1)
05
101520253035404550
0 200 400 600 800 1000 1200 1400Photosynthetic Photon Flux Density (μmol⋅m-2⋅s-1)
Stom
atal
Con
duct
ance
(m
mol
CO
2⋅m
-2⋅s
-1)
-1012345678
0 5 10 15 20 25 30 35 40 45 50Stomatal Conductance (mmol CO2 ⋅m-2⋅s-1)
Net
Pho
tosy
nthe
sis
(μm
ol C
O2⋅
m-2⋅s
-1)
0.00.10.20.30.40.50.60.70.80.9
Tran
spira
tion
(mm
olH
2O⋅m
-2⋅s
-1)Photosynthetic Photon Flux Density
PhotosynthesisTranspiration
( /100)1 n sss s
A h Pg m br c= = +
min( , )n c j dA w w R= −
max *( )(1 / )
ic i c i o
V cw c K O K−Γ= + +
**
( )4( 2 )
ij i
J cw c−Γ= + Γ
RuBP
regeneration-limited rate is
rubisco-limited rate is
wc
is the rubisco-limited rate of photosynthesis, wj
is light-limited rate allowed by RuBP
regeneration
Light Response Curve
02468
101214161820
0 100 200 300 400 500 600 700 800 900 1000
Photosynthetic Photon Flux Density (μmol photons⋅m-2⋅s-1)
Phot
osyn
thes
is (μ
mol
CO
2⋅m
-2⋅s
-1)
Wj
Wj
Wc
Leaf stomatal resistance
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
0
1
2
3
4
5
6
7
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75Leaf Area Index
Hei
ght (
met
ers)
0
1
2
3
4
5
6
7
0 1 2 3 4 5Cumulative Leaf Area Index
Hei
ght (
met
ers)
0 20 40 60 80 100Percent Of Full Solar Radiation
LAIRadiation
Oak Forest
Canopy resistance
Bonan
(2008) Ecological Climatology. 2nd edition (Cambridge Univ. Press)
Leaf photosynthesis and conductance response toatmospheric CO2
concentration, light-saturated
(a)
Dependence of leaf-scale photosynthesis for C3
and C4
vegetation on external CO2
concentration(b)
The C3
photosynthesis curves for unadjusted (C and P) and down-regulated (PV) physiology
(c
)
Dependence of
stomatal
conductance on CO2
concentration for the unadjusted and down-
regulated cases.
Bounoua et al. (1999) J Climate 12:309-324
CO2
fertilization and stomatal conductance
Photosynthesis increases and stomatal
conductance decreases with higher atmospheric CO2
Amazonian evergreen forest, diurnal cycle January
Canadian evergreen forest, diurnal cycle July
Bounoua et al. (1999) J Climate 12:309-324
CO2
fertilization and stomatal conductanceCO2
fertilization (RP, RPV) reduces canopy conductance and increases temperature compared with radiative CO2
(R)
CO2
fertilization and stomatal conductance
Bounoua et al. (1999) J Climate 12:309-324
Global climate:Reduced conductanceReduced evaporationReduced precipitationWarmer temperature
Fourth-generation of models
Vegetation dynamics
0
0.3
-10 25 60Temperature (°C)
μgC
O2⋅
g-1⋅s
-1 Root
HeterotrophicRespiration
Ecosystem carbon balance
Growth Respiration
μgC
O2⋅
g-1⋅s
-1
0 1 2Foliage
Nitrogen (%)
0 15 30Temperature
(°C)
μgC
O2⋅
g-1⋅s
-1
0 500 1000Ambient
CO2 (ppm)
Photosynthesis
0 -1 -2
Foliage Water Potential (MPa)
μgC
O2⋅
g-1⋅s
-1
0 15003000Vapor Pressure
Deficit (Pa)
46
20
0 500 1000PPFD
(μmol⋅m-2⋅s-1)
46
20
46
20
Sapwood
0
0.01
-10 25 60Temperature (°C)
μgC
O2⋅
g-1⋅s
-1Foliage
0
0.5
-10 25 60Temperature (°C)
μgC
O2⋅
g-1⋅s
-1
0 15 30Temperature
(°C)
Rel
ativ
e R
ate
1
8
Soil Water (% saturation)
Rel
ativ
e R
ate
0 1000
1
AutotrophicRespiration
Litterfall
NutrientUptake
Dynamic vegetation
Leaf phenology
Needleleaf evergreen treeBroadleaf deciduous tree
1
2
3
4
5
6
0
Leaf
Are
a In
dex
Jan
Feb
Mar Ap
rM
ay Jun
Jul
Aug
Sep
Oct Nov
Dec
Foley et al. (1996) GBC 10:603-628Levis et al. (1999) JGR 104D:31191-31198Levis et al. (2000) J Climate 13:1313-1325Cox et al. (2000) Nature 408:184-187
BIOGEOPHYSICS
20-minutes YearlyDaily
VEGETATION DYNAMICS
summergreen rain green
PHENOLOGYdaily leaf area index
canopy physiologyphotosynthesis
(GPP)stomatal
conductancemaximum leaf area
index
plant functional type (presence, extent)heightplant carbonlitter and soil carbon
canopy physicsenergy balance
temperaturewater
balanceaero-
dynamicsradiativetransfer
T, u,v, q, P S↓, L↓, (CO2 )
λ⋅E, H, τx ,τy , S↑, L↑, (CO2 )
ATMOSPHERE
soil/snow/ice physicsenergybalance
waterbalance
temperature
BIOGEOCHEMISTRY
heterotrophic respiration (RH )litter carbon soil carbon
autotrophic respiration (RA )maintenance•foliage,stem,root
growthnet primary production
GPP-RA
DAILY STATISTICS•10-day mean temperature •10-day mean photosynthesis•growing degree-day accumulation
ANNUAL STATISTICS
•minimum monthly temperature (20-year mean)•growing degree-days above 5°C (20-year mean)•precipitation•growing degree-days above heat stress
GPP soil waterleaf temperaturesoil temperature
•leaves•stems•roots•seeds
allocation turnover•leaf litter•sapwood toheartwood•root litter
mortality•growth efficiencybioclimatology•frost tolerance•heat stress
ecophysiology
•fire season length•net primary production•GPP and potential GPP
bioclimatology
phenology
fire probability
•potential rate•canopy gapbioclimatology•frost tolerance•heat stress•winter chilling•growing season warmth•low precipitation
establishment
soil organic matter
soil
litteraboveground space
competition
•moisture•fuel load
occurrence
fire resistancemortality
plant, littercombustion
fire
Net CO2
GPP-RA -RH
Bonan et al. (2003) Global Change Biology 9:1543-1566
Greening of a land surface model
Bonan et al. (1997) J Geophys
Res
102D:29065-29075
Model validation –
tower fluxes
Model
TowerObservations
Boreal Ecosystem Atmosphere Study (BOREAS)
Simulated Leaf Area Index
Three types of phenology• Evergreen• Raingreen• Summergreen
Bonan et al. (2003) Global Change Biology 9:1543-1566
Vegetation Type Simulated Observed
Tropical broadleaf evergreen forest 1278 1250±900
Tropical broadleaf deciduous forest 886 825±475
Temperate broadleaf deciduous forest 579 600±325
Boreal deciduous forest 346 425±200
Boreal needleleaf evergreen forest 385 325±200
Temperate/boreal mixed forest 576 525±275
Grassland 175 575±475
Tundra 159 150±200
Annual net primary production (g C m-2
yr-1)
Bonan et al. (2003) Global Change Biology 9:1543-1566
Model validation –
global net primary production
Vegetation dynamics
Boreal forest succession Global biogeography
Bonan et al. (2003) Global Change Biology 9:1543-1566
Climate 6000 years BPIncreased Northern Hemisphere summer solar radiation Strengthened African monsoonWetter North African climate allowed vegetation to expand
Greening of North Africa
Kutzbach
et al. (1996) Nature 384:623-626
Climate model experiments show:• Strengthened monsoon due to radiative forcing•
Vegetation forcing similar in magnitude to radiative forcing
Two climate model experimentsDesert North AfricaGreen North Africa
6kaBP DynVeg Soil Texture –
0 kaBP
Precipitation Change From Present Day
Dominant forcingIncrease in evaporationDecrease in soil albedo
Greening of North AfricaPresent Day Biogeography
(percent of grid cell)
Orbital geometry
Vegetation and soilAlbedo
Levis et al. (2004) Climate Dynamics 23:791-802
Vegetation masking of snow albedoMaximum satellite-derived surface albedo
during winter
Robinson & Kukla (1985) J Climate Appl
Meteor 24:402-411
Tree-covered land has a lower albedo
during winter than snow-covered land
Effect of boreal forests on climate
Colorado Rocky Mountains
Effect of boreal forests on climate
Climate Model Simulations: Forested - Deforested
-2
0
2
4
6
8
10
12
14
010203040506070Latitude (degrees N)
Tem
pera
ture
Diff
eren
ce (°
C) January
AprilJulyOctober
Bonan et al. (1992) Nature 359:716-718
Climate model simulations show boreal forest warms climate
Forest warms climate by decreasing surface albedoWarming is greatest in spring but is year-roundWarming extends south of boreal forest (about 45°N)
Boreal forest expansion with 2×CO2
warms climate
Bonan & Levis, unpublished
Mean annual temperature (2×CO2
)
Additional temperature change with vegetation
Dominant forcingDecrease in albedo[Carbon storage could mitigate warming]
Effect of boreal forests on climate
Land cover change as a climate forcing
Future IPCC SRES Land Cover Scenarios for NCAR LSM/PCM
Land cover change as a climate forcing
Feddema et al. (2005) Science 310:1674-1678
Forcing arises from changes in
Community compositionLeaf areaHeight [surface roughness]
↓Surface albedoTurbulent fluxesHydrologic cycle
Also alters carbon pools and fluxes, but most studies of land cover change have considered only biogeophysical processes
SRES B1 SRES A2
2100
2050
PCM/NCAR LSM transient climate simulations with changing land cover. Figures show the effect of land cover on temperature
(SRES land cover + SRES atmospheric forcing) -
SRES atmospheric forcing
Land use climate forcing
Dominant forcingBrazil –
albedo, ETU.S. –
albedoAsia -
albedo
Feddema et al. (2005) Science 310:1674-1678
Carbon cycle feedbackThree climate model simulations to isolate the climate/carbon-cycle feedbacks• Prescribed CO2
and fixed vegetation (a 'standard' GCM climate change simulation)• Interactive CO2
and dynamic vegetation but no effect of CO2
on climate (no climate/carbon cycle feedback)• Fully coupled climate/carbon-cycle simulation (climate/carbon cycle feedback)
Prescribed CO2
and fixed vegetationInteractive CO2
and vegetation, no climate changeFully coupled
Carbon budgets for the fully coupled simulation
Effect of climate/carbon-cycle feedbacks on CO2
increase and global warming
Cox et al. (2000) Nature 408:184-187