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Developing countries are facing a "double whammy" of growing population and an increase in climate change impacts, says an article in Nature Climate Change.

But local-level information about who the most vulnerable are and where they live is either lacking or lying unanalysed.

Now, some researchers are combining demographic data — which includes information on population size, birth and death rates, migration and age structures — with geographic and spatial data to identify where climate change might hit the hardest.

In China, for example, coastal city populations have been growing twice as fast as elsewhere, even though climate change is likely to increase the risk of extreme flooding and cyclones in these areas. West Africa is facing a similar situation, in the fast-growing cities of Burkina Faso and Niger.

Overall, some 13 per cent of people live in high-risk coastal areas, which make up only two per cent of the world's land — and 75 per cent of them are in Asia, according to UN figures.

"Overlapping poverty data with satellite data yields a map that could help governments and organisations to respond appropriately to disaster by targeting the poorest communities with their interventions," says the article.

Deborah Balk, a population and climate researcher at the City University of New York, United States, has put together the GRUMP (Global Rural–Urban Mapping Project) dataset, by collecting population data from regional censuses and land elevation information from satellites, and by looking for regions that are most illuminated at night to identify urban areas.

Her results reveal that cities in low-lying coastal areas are growing the fastest. Five times more people are living in poverty in the Mekong Delta, Vietnam, for example, than outside such zones. The situation is similar in Medan, Indonesia.

In Asia, "one in ten people, and one out of every eight urban dwellers, lives on the coast no more than ten metres above sea level, and that number is increasing," says Gordon McGranahan, Balk's colleague. "People are running towards risk, particularly in China, but also in other parts of the world such as Bangladesh, where more than 40 per cent of the land area is within ten metres of sea level."

Meanwhile, many areas in Africa are facing water shortage, and climate change may stir conflicts and mass migration.

Having reliable data on where people are at risk may help populations adapt and speed up disaster relief efforts, says Mark Montgomery, an economics professor at the State University of New York, United States. Social scientists may be able to tell relief agencies where to go, who lives there and what makes them vulnerable, he says.

Link to full article in Nature Climate Change