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Predictions Off for Global Warming Flood Risk - Study

Date: 30-Aug-07
Country: UK
Author: Michael Kahn

They found higher levels of the greenhouse gas predicted for
the end of the century will lead to an increase in the amount of
water that plants hold in the soil, said Richard Betts, a
meteorologist at Britain's Met Office who led the study.

This means areas expected to see increased rainfall might
have more severe flooding while droughts in other regions may
not be as bad, he said in a telephone interview.

"People may be underestimating flood risks because they do
not expect the soil to be as saturated as it might be," Betts
said. "We also suggest the conservation of water by plants would
partly offset the scarcity during a drought."

The findings underscore the need to take a wider view of
climate change to better understand and predict the impact of
rising temperatures, he added.

Using global climate models linked to data on vegetation and
soil content, the team of British researchers measured the
effect of carbon dioxide levels expected to rise dramatically by
the end of the century.

During photosynthesis -- the process through which plants
absorb energy and produce oxygen -- carbon dioxide enters plants
through tiny pores called stomata. Water eventually evaporates
back into the atmosphere through these stomata.

But higher levels of carbon dioxide in the air cause these
tiny holes to not open as widely, leading to reduced water loss
from the plant and leaving more water in the soil, Betts said.

Greenhouse gases such as carbon dioxide are widely blamed
for global warming. Scientists say average temperatures will
rise by between 2-6 degrees Celsius by the end of the century,
causing droughts, floods and violent storms.

"Climate change is more than just a change in the
meteorological conditions. It is also a change in the whole
ecology" Betts said. "We need to study this to get the whole
picture because this hasn't been looked at before."

With plants extracting less water from the soil, the surplus
water will drain into rivers and increase global flows another 6
percent on top of the 11 percent rise already predicted due to
global warming, Betts said.

The study did not indicate which areas might experience the
greatest change but Betts said this was the next step for his
team.

"We will need to quantify things and look at things like
water availability and the details of how intense rainfalls may
turn into flash floods," he said.

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