June 9, 2004

Gretchen Cook-Anderson 
Headquarters, Washington
(Phone: 202/358-0836)

Rob Gutro/Mike Bettwy
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-4044) 

RELEASE: 04-183

NASA DATA SHOWS DEFORESTATION AFFECTS CLIMATE IN THE AMAZON

NASA satellite data are giving scientists insight into how large-scale 
deforestation in the Amazon Basin in South America is affecting 
regional climate. Researchers found during the Amazon dry season last 
August, there was a distinct pattern of higher rainfall and warmer 
temperatures over deforested regions. 

Researchers analyzed multiple years of data from NASA's Tropical 
Rainfall Measuring Mission (TRMM). They also used data from the 
Department of Defense Special Sensor Microwave Imager and the 
National Oceanic and Atmospheric Administration's Geostationary 
Operational Environmental Satellites. 

The study is in a recent American Meteorological Society Journal of 
Climate. Lead authors, Andrew Negri and Robert Adler, are research 
meteorologists at NASA's Goddard Space Flight Center (GSFC), 
Greenbelt, Md. Other authors include Liming Xu, formerly with the 
University of Arizona, Tucson, and Jason Surratt, North Carolina 
State University, Raleigh.

"In deforested areas, the land heats up faster and reaches a higher 
temperature, leading to localized upward motions that enhance the 
formation of clouds and ultimately produce more rainfall," Negri 
said. 

The researchers caution the rainfall increases were most pronounced in 
August, during the transition from dry to wet seasons. In this 
transition period, the effects of land cover, such as evaporation, 
are not overwhelmed by large-scale weather disturbances that are 
common during the rest of the year. While the study, based on 
satellite data analysis, focused on climate changes in the deforested 
areas, large increases in cloud cover and rainfall were also observed 
in the naturally un-forested savanna region and surrounding the urban 
area of Port Velho, Brazil, particularly in August and September. 

Recent studies by Dr. Marshall Shepherd cited similar findings, 
including an average rain-rate increase of 28 percent downwind of 
urban areas and associated changes in the daily timing of cloud 
formation and precipitation. He is also a research meteorologist at 
GSFC.

This research confirmed the Amazon savanna region experienced a shift 
in the onset of cloudiness and rainfall toward the morning hours. The 
shift was likely initiated by the contrast in surface heating across 
the deforested and savanna region. 

The varied heights of plants and trees in the region change the 
aerodynamics of the atmosphere, creating more circulation and rising 
air. When the rising air reaches the dew point in the cooler, upper 
atmosphere, it condenses into water droplets and forms clouds.

Negri acknowledged other factors are involved. The savanna in this 
study is approximately 100 kilometers (62 miles) wide, the perfect 
size to influence precipitation, such as rain showers and 
thunderstorms. Earlier studies hypothesized certain land surfaces, 
such as bands of vegetation 50 to 100 kilometers (31-62 miles) wide 
in semiarid regions, could result in enhanced precipitation.

This research is in agreement with the recent and sophisticated 
computer models developed by the Massachusetts Institute of 
Technology. The models concluded small-scale circulations, including 
the mixing and rising of air induced by local land surfaces, could 
enhance cloudiness and rainfall. Many earlier studies that relied on 
models developed in the 1990s or earlier concluded widespread 
deforestation of the Amazon Basin would lead to decreased rainfall.

"The effects here are rather subtle and appear to be limited to the 
dry season. The overall effect of this deforestation on annual and 
daily rainfall cycles is probably small and requires more study," 
Negri said. Future research will use numerical models for 
investigating the linkage between deforested land surface and the 
cloud-precipitation components of the water cycle.

NASA's Earth Science Enterprise is dedicated to understanding the 
Earth as an integrated system and applying Earth System Science to 
improve prediction of climate, weather, and natural hazards using the 
unique vantage point of space.

For more information and images about this research on the Internet, 
visit: 

hthttp://www.gsfc.nasa.gov/topstory/2004/0603amazondry.html 

For information about NASA and agency programs on the Internet, visit: 

http://www.nasa.gov 

	
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