Quantifying Tropical Deforestation and Assessing Consequences for Climate

Ruth DeFries, Matthew Hansen, Doug Morton, Ellen Jasinski, Lahouari Bounoua (GSFC), 

Yosio Shimabukuro (INPE)

Clearing tropical forests for agriculture, logging, and settlements has major implications for climate, biodiversity, and other ecosystem services.  In this research, we are developing approaches to monitor deforestation through repeatable and automated analysis of satellite data.  Combining this information with ecosystem models allows us to assess the feedbacks from tropical deforestation to climate.

One aspect of this research, funded through the NASA LBA program in collaboration with the Brazilian government, aims to improve operational monitoring of deforestation in the Amazon basin through the use of coarse resolution data from MODIS. Complete coverage of the entire basin with MODIS data enables identification of locations undergoing deforestation for subsequent analysis with higher resolution data.  Tropical deforestation alters climate through several processes.  Burning and decaying vegetation accompanying deforestation emits carbon dioxide, a greenhouse gas, to the atmosphere.  The contribution of deforestation to the observed increase in atmospheric carbon dioxide is a major uncertainty in the global carbon budget, mainly due to uncertain rates of tropical deforestation.  Our research is combining the satellite-derived estimates of deforestation with terrestrial carbon models to improve estimates of carbon fluxes from deforestation and re-growth in tropical forests.

In addition to the effects on atmospheric carbon dioxide concentrations, tropical deforestation affects climate through altering exchanges of water, energy, and momentum between the land surface and the atmosphere.  Our research with climate models is quantifying the sensitivity of surface climate to these altered exchanges.

Example publications:  DeFries, R., Houghton, R.A., Hansen, M., Field, C., Skole, D.L. and Townshend, J.: 2002, Carbon emissions from tropical deforestation and regrowth based on satellite observations for the 1980s and 90s. Proceedings of the National Academy of Sciences, 99(22): 14256-14261; DeFries, R., Bounoua, L. and Collatz, G.J., 2002, Human Modification of the Landscape and Surface Climate in the Next Fifty Years. Global Change Biology 8: 438-458.