Throughout Asia, as well as the world as a whole, ever-growing numbers of people are moving to the cities in search of work and a better way of life.

Urban environments can provide enormous social opportunities and economic efficiencies, but the rapid growth of sprawling megacities in Asia and elsewhere is also producing a wide range of new challenges in such areas as housing, public health, transportation, infrastructure and governance.

By 2030, Asian cities will account for more than half of the world’s projected urban population of 4.9 billion, according to U.N. estimates. Two of the world’s largest emerging “mega-regions,” for example, are Hong Kong-Shenzhen-Guangzhou, with 120 million people, and Tokyo-Nagoya-Osaka-Kyoto-Kobe, with 60 million.

Dr. Eduardo Lopez Moreno, principal author of the U.N.’s State of the World’s Cities 2010/2011 report, told metropolitan leaders at an East-West Center seminar that cities are engines of growth and progress. However, he said, the U.N. report also confirms that impoverished urban slums continue to breed hunger, poor health and lagging education, along with a host of other social, environmental, cultural and political challenges. According to the report, 61 percent of the world’s slum population is in Asia, topping half a billion people.

While some of the best progress in helping to alleviate slum conditions has been in China, India, Indonesia and Vietnam, on a global basis the numbers of slum dwellers and the inequalities within cities continue to grow, Moreno said, particularly when it comes to education. Studies across the world’s biggest urban areas found that just 20 percent of slum children go to school, while 70 percent of children in other parts of the same cities are enrolled.

Moreno said that four factors determine success in improving the lives of slum dwellers: recognition of the problem, help from national governments and institutions, the location, and monitoring of clear goals and resource allocation.

"For me, a fundamental challenge in the coming years will be what kind of paradigm shift will be necessary in order to deal with regional governance, but linked to city development," he said.

Meanwhile, many of Asia’s largest cities are located in coastal and low-lying areas that are particularly vulnerable to natural disasters and climate change effects such as sea-level rise and intensified storms.

But in many of these cities, appropriate risk-reduction measures have not been implemented or even seriously considered, according to a recent policy brief by East-West Center researcher Roland Fuchs.

Among the barriers, Fuchs writes, are a lack of awareness, the immediacy of other problems such as housing, transportation and poverty, budgetary constraints, and a lack of appropriate governance structures and technical skills.

According to Fuchs, reducing the risk of large disasters will require the thorough incorporation of climate risk management into urban planning and governance.

"This will depend in part on the scientific community providing improved urban-scale predictions of risks," he writes, "but also, more importantly, on political leadership recognizing the growing threats of climate change, developing a coherent strategy … and mobilizing the necessary resources."

Finally, the density of mega-city environments can make them fertile breeding grounds for emerging infectious diseases. Many diseases — such as H5N1 "bird" flu and SARS — have emerged in Asia, where landscapes are in transition and domestic animals are often found in close proximity to human population centers.

In the early 1990s, EWC researchers began exploring risk-assessment methods for what they termed the "dark middle" of development, where the risks of poverty and rural lifestyles persist alongside new risks created by modernization.

Building on that idea, researcher Jeff Fox is leading a project to investigate the interaction of urbanization, agricultural change and habitat alteration with outbreaks of bird flu in Vietnam.

"Studying the role of societal development in disease transmission is urgent and critical for designing policies to prevent and manage outbreaks," Fox says.