The number of people under threat from major flooding will double to two billion within 50 years, the UN warns.
The recent floods in Haiti could be replicated in many places
The world will be warmer and wetter by mid-century with the result that there will be more storms, a report by the Tokyo-based UN University says.
The study warns that small island states and coastal regions are most at risk - particularly in Asia.
The threat comes from rising sea levels, continuing deforestation and population growth.
The report finds that :
- One billion people - a sixth of the world's population - currently live in the path of potential major flood disasters
Most of those at risk are among the world's poorest
Floods already kill as many as 25,000 people a year
There were six major flood disasters in the 1950s, seven in the 1960s, eight in the 1970s, 18 in the 1980s and 26 in the 1990s
One of the report's authors, Janos Bogardi, called for "greater global capacity to monitor and forecast extreme events".
The UN University was established in 1973 to study global threats.