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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


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


• 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


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


μgC

O2⋅

g-1⋅s

-1Foliage

0

0.5


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


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


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




CO2 H2 O

Moist Air

Dry Air


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


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


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


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


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


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


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



CO2 H2 O

Moist Air


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


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


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


CO2

fertilization and stomatal conductanceCO2

fertilization (RP, RPV) reduces canopy conductance and increases temperature compared with radiative CO2

(R)

CO2

fertilization and stomatal conductance


Global climate:Reduced conductanceReduced evaporationReduced precipitationWarmer temperature

Fourth-generation of models

Vegetation dynamics

0

0.3


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


μgC

O2⋅

g-1⋅s

-1Foliage

0

0.5


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


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)


Model validation –

global net primary production

Vegetation dynamics

Boreal forest succession Global biogeography


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


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]


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

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