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Climate change is likely to worsen floods on rivers such as the Ganges, the Nile and the Amazon this century while a few, including the now-inundated Danube, may become less prone, a Japanese-led scientific study said on Sunday.
The findings will go some way to help countries prepare for deluges that have killed thousands of people worldwide and caused tens of billions of dollars in damage every year in the past decade, experts wrote in the journal Nature Climate Change.
Given enough warning, governments can bring in flood barriers, building bans on flood plains, more flood-resistant crops and other measures to limit damage.
Overall, a "large increase" in flood frequency is expected in south-east Asia, central Africa and much of South America this century, the experts in Japan and Britain wrote.
Severe floods would happen more often on most of the 29 rivers reviewed in detail, including the Yangtze, Mekong and Ganges in Asia, the Niger, the Congo and the Nile in Africa, the Amazon and the Parana in Latin America and the Rhine in Europe.
Flooding would become less frequent in a handful of river basins including the Mississippi in the United States, the Euphrates in the Middle East and the Danube in Europe.
The experts predicted that northwestern Europe, where the Rhine flows, would be damper while a band from the Mediterranean Sea through eastern Europe - including the Danube region - into Russia would be drier.
The scientists said there were wide bands of uncertainty.
EUROPEAN FLOODS
On Sunday, the Danube was set to peak at record high levels in Budapest amid severe floods in the region. Tens of thousands have been forced to leave their homes and at least a dozen people have died in floods that have hit Germany, Austria, Slovakia, Poland and the Czech Republic over the last week.
Climate scientists say that, overall, rising temperatures increase the risk of floods because warmer air can absorb more moisture and so cause more rain. Changes in winds and other factors mean some areas are likely to get wetter, others drier.
Experts have struggled to predict how individual rivers will react because that requires an understanding of flows in each catchment area, lead author Yukiko Hirabayashi of Tokyo University told Reuters in a telephone interview.
"Small rivers in Japan can be affected by heavy precipitation over hours or days," she said. "But for the large river basins, floods are triggered by monthly trends."
A 2012 report about extreme events by a U.N. panel of scientists said there was only "low confidence" in projections of changes in river flooding because of many uncertainties.
Professor Mojib Latif, a meteorologist at the Helmholtz Center for Ocean Research in Germany, who was not involved in the study, said another problem is that there are few reliable rainfall records on which to build forecasts.
Still, he predicted that floods like those now in Europe would become more likely as temperature rise. "We're seeing an increase in flooding events ... Research shows that the probability of heavy precipitation will increase," he said.
Worldwide, average surface temperatures have risen by 0.8 degree Celsius (1.4 F) since the Industrial Revolution, a trend the U.N. panel of experts blames mainly on human emissions of greenhouse gases from cars, factories and power plants.
