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Get ready: Climate change to boost river flooding

Projected return period (in years) in the 21st century for river discharges matching what in the 20th century were 100-year floods.
Projected return period (in years) in the 21st century for river discharges matching what in the 20th century were 100-year floods.Dr Sujan Koirala

By Larry O'Hanlon

Discovery News

Climate change is going to bring more river flooding, says a team of scientists who have employed no fewer than 11 separate climate models to study the decades ahead.

“Floods are among the most major climate-related disasters,” writes Yukiko Hirabayashi of The University of Tokyo and lead author of a paper in Sunday's issue of the journal Nature Climate Change. “In the past decade, reported annual losses from floods have reached tens of billions of U.S. dollars and thousands of people were killed each year.”

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This, and the fact that the primary worldwide organization that studies such things –the Intergovernmental Panel on Climate Change (IPCC) – has pointed out the need for better projections of river flooding, served as motivation for the new study.

What the researchers found was an increase in the frequency of flooding rivers in Southeast Asia, Peninsular India, eastern Africa and the northern half of the Andes. At the same time, river flood frequencies will drop in parts of northern and Eastern Europe, Anatolia, Central Asia, central North America and southern South America.

In terms of the number of people exposed to flood risks, they found that depends on the temperatures to which things heat up. With a 2-degree Celsius rise in temperature, about 27 million people will be exposed to more floods. With a 4 degrees C warming the exposure rises to 62 million and at 6 degrees C it is up to 93 million people.

The climate models were also used to study the outlets of some river basins. There they saw the frequency of floods increasing during the 21st century in just about every selected rivers in South Asia, Southeast Asia, Oceania, Africa and Northeast Eurasia. They also predict that what were considered 100-year floods in the 20th century will occur every 10 to 50 years in the 21st century.

“This is very important and useful information, and shows that policymakers should take climate change into account when developing adaptation strategies,” said flood researcher Brenden Jongman of VU University of Amsterdam. “Also, the analysis of changes in flood frequency on a global scale is very important – this shows that in many developing countries the frequency of extreme events might be increasing.”

While the latest IPCC report still states that ‘global warming might lead to higher flood frequencies and intensities, Jongman explained, this work finally puts real numbers on the flooding.

“It shows that flood frequencies, flood extents and population exposure will increase under all climate (change) scenarios,” said Jongman.