impact of deforestation on the regional climate over the congo basin
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Impact of Deforestation on the Regional Climate over the Congo Basin
Wenxian ZhangSchool of Earth and Atmospheric Sciences
Georgia Institute of TechnologyApril 22, 2008
2
Background
• Land and atmosphere interact in many aspects. Their interactions are important to regional climate.
• Regional climate are sensitive to land cover change, such as deforestation. Currently, deforestation is threatening the tropical forest in many countries.
3
Background
• Due to the lack of direct observations and with the development of land models, modeling has become a primary approach to study land-atmosphere interaction.
• Numerous studies simulated the impact of deforestation on the regional climate in the Sahel, Amazon, and East Asia. Most of the results indicated a decrease in precipitation.
4
Motivations
• To simulate a deforestation case in the Congo Basin
• To analyze the response of local climate to deforestation
- Hydrological cycle
- Surface energy balance
5
Model Description
• A coupled run of the Community Land Model Version 3.3 (CLM3.3)
• A time period from 1979 to 1989; First Two years for spinning up
• Tow cases: control and modification
6
Model Description
• Change the PFT from Broadleaf evergreen tropical trees to C3 grass
• Change the leaf area index (LAI) and the stem area index (SAI) according to the modification to the PFT
7
Land States
• Increase
- Soil moisture
- Runoff
- Ground evaporation
- Albedo• Decrease
- Canopy Interception
- Transpiration
- Canopy evaporation
- LAI• Nearly the same
- Precipitation
- Evaporation
8
Land States
• Increase
- Upward SW and LW
- Net SW and LW
- Bowen ratio
- Emissivity• Decrease
- Latent Heat• Slightly decrease
- Sensible heat
9
Land States
• Increase
- Absorbed Infrared
radiation
- Sensible heat flux from
ground
- Ground temperature
- Surface wind• Decrease
- Photosynthesis
- Sensible heat flux from
vegetation• Slightly increase
- Absorbed solar
radiation
10
Atmosphere States
• Slightly Increase
- High cloud cover
- Convective precipitation
- PBLH
- Surface air temperature• Decrease
- Low cloud cover
- Large-scale precipitation• Remain the same
- Precipitable water
- Planetary albedo
11
Surface Water and Energy Budgets
Surface Water Budget Surface Energy Balance
12
Ratios
• The ratios of transpiration
and canopy interception to precipitation are sensitive to deforestation.
• ET is the dominant component to balance precipitation.
• Latent heat flux is dominant in wet seasons.
• The trends of ratios for SH and LH are opposite
13
Conclusions
• Deforestation causes an increase in soil water storage, a decrease in canopy interception and transpiration, and redistribution of evaporation.
• Precipitation and runoff do not show much difference.
• Deforestation leads to an increase in surface albedo, surface long-wave emissivity, and Bowen ratio.
• ET is the dominant term to balance precipitation; Latent heat flux is dominant to balance surface net radiation in wet seasons.
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