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Models Calculate Deforestation's Impact on Kilimanjaro

04.03.2011
The impact that local deforestation might have on the snowcap and glaciers atop Mount Kilimanjaro are being calculated at The University of Alabama in Huntsville using regional climate models and data from NASA satellites.

The first piece of that research, which looked only at the month of July, found that deforestation is changing weather patterns around the mountain but not (at least in July) at the peak, according to Dr. Udaysankar Nair, a research scientist in UAHuntsville's Earth System Science Center.

Early results from this work, which is funded through NASA's Earth Science Directorate, were published Feb. 15 in the "Journal of Geophysical Research."

The current glaciers of Kilimanjaro, made famous by an Ernest Hemingway short story in 1936 and a movie released in 1952, are almost 12,000 years old. At their maximum, the mountain's glaciers and ice cap covered about 400 square kilometers and reached from the summit (19,298 feet above sea level) to the surrounding plain more than 9,000 feet below. About 16,000 years ago, during the most recent ice age, Kilimanjaro's glaciers covered up to 150 square kilometers.

A tiny fraction of that ice cap still exists. Surveys in the 1880s estimated that glaciers covered about 20 square kilometers on the mountain. From 1912 to now, the glacier area on Kilimanjaro has decreased from 12 square kilometers to less than two.

Nair and doctoral student Jonathan Fairman, a NASA Earth system science fellow, are studying the effects of deforestation on weather patterns in a 2,000-square-mile area around the mountain.

In collaboration with UAHuntsville's Dr. Sundar Christopher and Dr. Thomas Mölg at the University of Innsbruck, Austria, they use data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard two NASA satellites to determine the surface characteristics of both forested and deforested land in the area around the mountain.

That data is used to digitally add or remove tracts of indigenous land cover within computer models of the regional weather. That lets them compare existing weather patterns to patterns that might exist if no trees had been cut down or if all of the surrounding forests were razed. The UAHuntsville team also uses MODIS data to evaluate how well the model simulates cloud formation and weather patterns over Kilimanjaro under current conditions.

They decided to start by looking at July, during the summer "dry" season. That is when weather around the mountain is influenced least by large-scale regional weather systems from the Indian Ocean.

"We figured that the impact of local systems -- such as deforestation -- would be greater when large scale weather events aren't there," Nair explained.

In July the prevailing wind across the high plains of northern Tanzania is from the south. The models show that during that month deforestation around the mountain is shifting cloud cover and precipitation up the south side of the mountain. Modeling of weather patterns on the windward side of Kilimanjaro shows a decrease in rain and cloudiness at levels up to 6,500 feet above sea level, but an increase in rainfall and cloud cover from 6,500 to about 13,000 high.

July rainfall on the north side of the mountain has decreased at higher elevations (5,850 to 13,000 feet) in response to deforestation. There is little precipitation at the peak during July and the models indicate that hasn't changed in response to deforestation.

"Kilimanjaro is an isolated mountain, so under normal circumstances most of the local air flow goes around the mountain," Nair said. "When you cut down forests you reduce surface roughness, which increases wind speed at higher elevations on the windward slopes. That faster wind over steep upper slopes causes more intense cloud formation and precipitation up the side of the mountain."

Nair and Fairman are extending their model runs to include the fall and spring rainy seasons, when the dominant weather rolls in from the Indian Ocean.

"We need to look at the complete annual cycle before we understand the impacts that deforestation is having on the mountain peak," Fairman said.

Early results suggest that deforestation around Kilimanjaro might be having a noticeable impact on how quickly glaciers and ice are melting on the mountain, although it isn't clear from preliminary data modeling whether that impact is positive or negative.

"When we look beyond the summer dry season, our results suggest that regional deforestation has the potential to either mitigate or enhance large scale climate change," said Nair. "In some places, like Costa Rica, deforestation clearly adds to the effects of climate change. For Kilimanjaro, we expect our extended model simulations to reveal whether deforestation will worsen or mitigate large scale changes."

Earlier research by Nair and other scientists at UAHuntsville found that deforestation in Costa Rica is increasing some impacts of large-scale climate change in the mountain range that is home to that country's cloud forests. Unlike Kilimanjaro, however, the Costa Rican mountains are a range that the prevailing wind cannot blow around.

Dr. Udaysankar Nair
(256) 961-7841
nair@nsstc.uah.edu

Dr. Udaysankar Nair | Newswise Science News
Further information:
http://www.uah.edu

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