Predictions off for global warming flood risk-study

LONDON, Aug 29 (Reuters) Current predictions for global warming underestimate the risk of floods and overestimate the impact of droughts by not taking into account the role plants play in absorbing carbon dioxide, researchers today said.

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 per cent 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.

Reuters SY GC2356