* World's fastest growing populations increasingly at risk
* Africa and Asia most vulnerable to more extreme weather
* Survey can help city planners, investors adapt to wilder weather
By David Fogarty
SINGAPORE, Oct 26 (Reuters) - Rapidly growing megacities in Africa and Asia face the highest risks from rising sea levels, floods and other climate change impacts, says a global survey aimed at guiding city planners and investors.
The study by risk analysis and mapping firm Maplecroft, released on Wednesday, comes as the United Nations says the world's population will hit seven billion next week and as huge floods inundate areas of Thailand and the capital Bangkok.
The survey ranks nearly 200 nations in terms of vulnerability to climate change over the medium term.
It also ranks the top-20 fastest-growing cities by 2020 in terms of risk, with the study based on a series of indices. The survey maps the world in 25-square-km segments according to vulnerability, making regional assessments easier.
Haiti is the country most at risk from climate change, while Iceland is the least vulnerable. Thailand is ranked 37th.
Dhaka, capital of Bangladesh, is the megacity most at risk with an "extreme" ranking. Other megacities at extreme or high risk include Manila, Kolkata, Jakarta, Kinshasa, Lagos, Delhi and Guangzhou.
"Population growth in these cities combines with poor government effectiveness, corruption, poverty and other socio-economic factors to increase the risks to residents and business," said Maplecroft.
This meant infrastructure, already stretched in many cities, would struggle to cope as populations increase, making disaster responses less effective at a time when disasters might become more frequent.
CONSEQUENCES
"The impacts of this could have far reaching consequences, not only for local populations, but on business, national economies and on the balance sheets of investors around the world, particularly as the economic importance of these nations is set to dramatically increase," Charlie Beldon, Maplecroft's principal environmental analyst, said in a statement.
Maplecroft analyses the exposure of populations to climate related natural hazards and sensitivity of countries in terms of population concentration, development, natural resources, agricultural dependency and conflict. They also rank in terms of a country's, city's or region's ability to adapt.
The maps highlight areas within countries that might be more vulnerable, allowing risks to towns, cities, economic zones and individual company assets to be identified.
For instance, Manila, as the Philippines' commercial centre, is extremely vulnerable because of its huge population, rapid growth -- estimated to add another 2.2 million people between 2010 and 2020 -- risk from flooding and storms and the likely increase in these disasters. Rainfall intensity is likely to increase in tropical Asia, climate scientists say.
Highlighting the areas of great risk also offered investment opportunities.
"Changing demands for goods and services can present opportunities for new products or innovative modifications to existing ones," Maplecroft says.
Globally, many other cities were also vulnerable to climate change, Maplecroft said, but better governance, greater wealth and better policies meant they were more able to adapt.
"It is not only cities in the developing world that are at risk from the potential effects of climate change," Beldon told Reuters in an email. "For example, the floods that struck Brisbane (Australia) in early 2011 illustrate the potential of hazards to cause devastation even in a developed country."
Miami still ranked at a high risk as does Singapore, while New York and Sydney were medium and London was a low risk.
Bangkok ranked extreme, and the Thai government has created a $10.6 billion budget to rebuild after the current floods subside.
(Editing by Nick Macfie)
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