Modeling land-atmosphere interactions:
the impact of deforestation in tropical
Africa on the regional climate.
Akkermans, T., Nouvellon, Y., Lauwaet., D., Van Lipzig, N.P.M.
MeteoClim PhD symposium, 05/11/2010, KMI/RMI, Ukkel (Brussels)
Introduction
• Deforestation: a climate forcing with regionally very different
consequences.
• This research: climatological impact of anthropogenic forest degradation in
tropical Africa.
– Until now, relatively few attention to this study area
– Building on previous studies, using additional and new research methods
• Focus on surface temperature and precipitation.
– How will deforestation affect regional temperatures?
– What is the joint effect of global warming and deforestation?
– Does the spatial pattern of deforestation matter?
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Introduction
• No forest
• Forest
– Less energy necessary for evapotranspiration (lower latent heat flux)
– More energy necessary for evapotranspiration (higher latent heat flux)
– More energy available to heat surface
(higher transmitted or sensible heat
flux)
– Less energy available to heat surface
(lower sensible heat flux)
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Introduction
• In order to answer the research questions, we need to simulate the present
climate and do projections for the future climate. Therefore we use a
regional climate model.
• The complete coupled model consists of two coupled parts:
– The atmospheric climate model: COSMO-CLM v.4.0, v.4.8
– A land-surface scheme: 1) TERRA, 2) Community Land Model or Comm.L.M. v.3.5
COSMO-CLM
Comm.L.M.
TERRA
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Introduction
1. Evaluation of the land-surface scheme separatly, in the
”standalone” mode
– Sensible heat flux (W/m²)
– Latent heat flux (W/m²)
– Soil water content
2. Evaluation of the coupled climate model: atmospheric part +
landsurface scheme
– Cloud cover (%)
– Precipitation (mm/day)
– Temperature
3. Finally, some preliminary experimental results are shown. In the
model, a large part of the tropical rainforest has been replaced with
grassland. However only a theoretical exercise, it will give a first
impression of the climate sensitivity to large-scale deforestation.
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• Conceptual representation of the
complete coupled model:
COSMO-CLM
Comm.L.M.
TERRA
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1. Evaluation of landsurface schemes
• First, we evaluate two possible land-surface schemes (Comm.L.M. and
TERRA) separatly from the atmospheric model: ”stand-alone” evaluation.
• Afterwards, the best performing scheme will be used in the coupled model.
COSMO-CLM
Comm.L.M.
TERRA
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Kissoko” (Rep. Of Congo)
– landcover: eucalyptus plantation
– PFT: 100% evergreen tropical tree
Natural forest
eucalyptus plantation
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Kissoko” (Rep. Of Congo)
– landcover: eucalyptus plantation
– PFT: 100% evergreen tropical tree
LH
SH
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Kissoko” (Rep. Of Congo)
– landcover: eucalyptus plantation
– PFT: 100% evergreen tropical tree
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Tchizalamou” (Rep. Of Congo)
– landcover: grass savannah
– PFT: 100% C4 grassland
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Tchizalamou” (Rep. Of Congo)
– landcover: grass savannah
– PFT: 100% C4 grassland
LH
SH
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Tchizalamou” (Rep. Of Congo)
– landcover: grass savannah
– PFT: 100% C4 grassland
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Mongu” (Zambia)
– landcover: Miombo woodlands
– PFT: 100% deciduous tropical tree
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Mongu” (Zambia)
– landcover: Miombo woodlands
– PFT: 100% deciduous tropical tree
LH
SH
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Mongu” (Zambia)
– landcover: Miombo woodlands
– PFT: 100% deciduous tropical tree
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Demokeya” (Sudan)
– landcover: sparse savannah
– PFT: 80% C4 grass, 20% deciduous
tropical tree
Dry season
Wet season
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1. Evaluation of landsurface schemes
• Measurements: eddy covariance (”flux
tower”) from CARBOAFRICA project:
– Site: ”Demokeya” (Sudan)
– landcover: sparse savannah
– PFT: 80% C4 grass, 20% deciduous
tropical tree
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• Conceptual representation of the
complete coupled model:
COSMO-CLM
Comm.L.M.
TERRA
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2. Coupled model evaluation (2005)
• Secondly, we evaluate the complete coupled model. The model should be
able to represent spatial variability of cloudiness, precipitation,
temperature, etc.
COSMO-CLM
Comm.L.M.
TERRA
• The lateral boundary conditions: ERA-interim reanalysis (75km res.)
• COSMO-CLM: 25km res., 210x180 grid points
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2. Coupled model evaluation (2005)
• Average cloud cover (0-1):
– Observations: MODIS satellite
• Average precipitation (mm/day):
– Observations: TRMM satellite
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2. Coupled model evaluation (2005)
• Cloud cover: difference between models and observations
COSMO-CLM 4.0 +
Comm.L.M.
COSMO-CLM 4.0 +
TERRA
COSMO-CLM 4.8 +
TERRA
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2. Coupled model evaluation (2005)
• Precipitation: difference between models and observations
COSMO-CLM 4.0 +
Comm.L.M.
COSMO-CLM 4.0 +
TERRA
COSMO-CLM 4.8 +
TERRA
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3. Deforestation experiment
• Now we run the coupled model (COSMOCLM + Comm.L.M.) twice..
– once with the original vegetation
– once with a modified vegetation
COSMO-CLM
Comm.L.M.
TERRA
.. and compare the surface climate of the two model runs.
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3. Deforestation experiment
• Now we run the coupled model (COSMOCLM + Comm.L.M.) twice..
– once with the original vegetation
– once with a modified vegetation, replacing forest with e.g. grass
COSMO-CLM
Comm.L.M.
TERRA
.. and compare the surface climate of the two model runs.
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3. Deforestation experiment
• Now we run the coupled model (COSMOCLM + Comm.L.M.) twice..
– once with the original vegetation
– once with a modified vegetation
COSMO-CLM
Comm.L.M.
TERRA
.. and compare the surface climate of the two model runs.
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3. Deforestation experiment
• Original PFT's (% of pixel
area):
– 1. Bare ground
– 5. Evergreen tropical tree
1
– 7. Deciduous tropical tree
– 14. non-arctic grass C3
– 15. grass C4C
5
7
14
15
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3. Deforestation experiment
• Modified PFT's (% of pixel
area):
– 1. Bare ground
– 5. Evergreen tropical tree:
-40%
1
– 7. Deciduous tropical tree
– 14. non-arctic grass C3
– 15. grass C4: +40%
5
7
14
15
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3. Deforestation experiment
• Modified PFT's (% of pixel area):
– 5. Evergreen tropical tree: -40%
– 14. non-arctic grass C3
– 15. grass C4: +40%
1
14
15
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3. Deforestation experiment
• Result on average latent heat flux:
– Local decrease from 8 - 12 W/m²
– Mean of 2005
Latent heat flux difference: deforested minus
reference model run (W/m²)
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3. Deforestation experiment
• Result on average latent heat flux:
– Local decrease from 8 - 12 W/m²
• Result on average sensible heat flux:
– Local increase from 1.5 - 3.5 W/m²
Sensible heat flux difference: deforested
minus reference model run (W/m²)
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3. Deforestation experiment
• Result on average latent heat flux:
– Local decrease from 8 - 12 W/m²
• Result on average sensible heat flux:
– Local increase from 1.5 - 3.5 W/m²
• Result on average 2m temperature:
– Local increase from 0.8 - 1.1 °C
Temperature difference: deforested minus
reference model run (W/m²)
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4. Conclusions and outlook
• Conclusions
– From the two land-surface schemes, the Community Land Model is doing a better job
than the standard TERRA scheme. Therefore, it will be preferred in the coupled climate
model to perform the long-term simulations.
– The performance of the atmospheric climate model over Africa should be better,
especially with respect to cloudiness, which is important for the surface energy
balance. However, the problems are mostly situated in ocean areas, whereas this
research focuses on continental areas.
– Preliminary deforestation experiments confirm existing literature.
• Outlook
– Development of a range of possible deforestation scenarios. Hereby, the goal is not
to establish a future state of the forest ”as realistic as possible” (the uncertainty over a
timespan of 50 years is anyway too high), but to get a good understanding of the
sensitivity of vegetation-climate feedbacks
– Performing the long-term runs (1989-2008, 2040-2060)
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Thanks for your attention!
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