Global warming will put millions more people at the risk of severe river flooding in the next 20 years, particularly in the US and parts of India, Africa and central Europe, a study has warned.
Already today, fluvial floods are among the most common and devastating natural disasters, researchers said.
Now, scientists from the Potsdam Institute for Climate Impact Research (PIK) in Germany have calculated the required increase in flood protection until the 2040s worldwide, breaking it down to single regions and cities.
They found that the need for adaptation is greatest in the US, parts of India and Africa, Indonesia, and in central Europe.
Inaction would expose many millions of people to severe flooding, the researchers said.
"More than half of the US must at least double their protection level within the next two decades if they want to avoid a dramatic increase in river flood risks," said Sven Willner from PIK, lead author of the study published in the journal Science Advances.
Without additional adaptation measures - such as enhancing dykes, improved river management, increasing building standards, or relocating settlements - the number of people affected by the worst 10 per cent of all river flooding events will increase in many places.
In Northern America, the number of affected people will increase from 0.1 to 1 million. While this seems not like a large number, it is a tenfold increase, researchers said.
Absolute values are even bigger elsewhere: in South America the number of people affected by flooding risks will likely increase from 6 to 12 million, in Africa from 25 to 34 million, and in Asia from 70 to 156 million, they said.
The real numbers might be even higher in the future as population growth and further urbanisation is not taken into account, researchers said.
The study is based on comprehensive computer simulations using existing data on rivers from a great number of sources.
"While this data is not perfect for each and every river in the remotest corners of our planet, it certainly is sufficient for places where a lot of people live, a lot of financial values are accumulated, and where flood risks are substantial, said Willner.
An increase in river flood risks over the next 2-3 decades will be driven by a number of greenhouse gases already emitted into the atmosphere, hence it does not depend on whether or not we limit global warming, researchers said.
"However, it is clear that without limiting human-caused warming to well below 2 degrees Celsius, river flood risks in our century will increase in many regions to a level that we cannot adapt to," said Anders Levermann, head of global adaptation research at PIK.