NORWAY: August 8, 2008


OSLO - Tropical downpours are becoming more frequent and the trend seems worse than expected, bringing greater risks of flash floods, scientists said on Thursday.


"As the tropics warm are are seeing an increased frequency in the heaviest rainfall," said Richard Allan of the University of Reading in England, who co-authored a study of tropical rains with Brian Soden of the University of Miami.

The satellite review of tropical rainstorms since the 1980s gave the first observational evidence to confirm computer models that predict more intense cloudbursts because of global warming stoked by human activities, they said.

Writing in the journal Science, they also said the trend to extreme soakings was stronger than predicted by computer models "implying that projections of future changes in rainfall extremes ... may be underestimated".

The findings were based on a study of the tropical oceans, where satellites can more easily record rainfall. Allan said the trends were likely to be matched over land.

The UN Climate Panel, drawing on the work of 2,500 scientists, said last year that rainfall was likely to get more intense in many tropical regions, raising risks of flash floods, erosion and mudslides.

The satellite data showed 2-3 times more intense downpours than predicted by the climate models, stoked by rising emissions of greenhouse gases from burning fossil fuels in cars, factories and power plants.

But Allan told Reuters that the finding that the models were too cautious was less certain than the conclusion that tropical rainfall had become more intense. Checks might be made on land by examining rain gauges or river flows, he said.


FARMING THREATENED

The UN Climate Panel says that shifts in rainfall patterns are likely to disrupt farming in many regions, affecting the livelihoods of hundreds of millions of people especially in Asia, Africa and Latin America.

"Flash flooding can cause damage to settlements and societies. It can contaminate ground water, drinking supplies, with potential health effects," Allan said.

"The spread of disease can be impacted by heavy rainfall," he added. "Very intense rainfall can destroy crops. There are also possibilities of enhanced erosion, degradation of soil".

Scientists say it is hard to link climate change to one-off events such as floods in the US Midwest that damaged millions of acres of cropland in June.

The UN Panel predicts more rain overall this century in many parts of the tropics and towards the polar areas with declines in middle latitudes such as the Mediterranean basin, the Western United States and southern Africa.

-- For latest Reuters environment blogs click on: http://blogs.reuters.com/environment/ (Editing by Andrew Roche)


Story by Alister Doyle, Environment Correspondent


REUTERS NEWS SERVICE