Impact of Deforestation on the Regional Climate over the Congo Basin

Wenxian ZhangSchool of Earth and Atmospheric Sciences

Georgia Institute of TechnologyApril 22, 2008

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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.

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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.

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Motivations

• To simulate a deforestation case in the Congo Basin

• To analyze the response of local climate to deforestation

- Hydrological cycle

- Surface energy balance

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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

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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

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Land States

• Increase

- Soil moisture

- Runoff

- Ground evaporation

- Albedo• Decrease

- Canopy Interception

- Transpiration

- Canopy evaporation

- LAI• Nearly the same

- Precipitation

- Evaporation

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Land States

• Increase

- Upward SW and LW

- Net SW and LW

- Bowen ratio

- Emissivity• Decrease

- Latent Heat• Slightly decrease

- Sensible heat

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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

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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

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Surface Water and Energy Budgets

Surface Water Budget Surface Energy Balance

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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

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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.