World Bank Frets Over Urban Flooding in Asia

In October of last year, flood waters covered much of this area outside of Bangkok.

Image Courtesy of J. Villalovos/U.S. Navy Visual News Service

TOKYO—"Flooding is the most common of natural disasters [and] it is increasingly an Asian phenomenon," Abhas Jha, a World Bank disaster management expert, said today at a briefing here, while unveiling a "tool kit" for policy makers eager to counter the problem.

Flooding strikes worldwide, of course, but Jha presented eye-opening statistics indicating the developing countries of Asia are particularly vulnerable: The seven most destructive floods of the past 30 years all occurred in Asia. Over the same period, 90% of those killed or affected by floods lived in Asia. The region also got hit with about half of the total worldwide economic loss due to flooding. The future doesn't look much better: currently 80% of the population of Bangladesh is at risk of flooding and 70% of Vietnamese.

The main reason for Asia's vulnerability to floods is the phenomenal movement of populations from rural areas to cities built on coasts and along rivers. "This puts a lot of people in harm's way," said Jha, who is the lead author of Cities and Flooding: A Guide to Integrated Urban Flood Risk Management for the 21st Century. The new report was released in Tokyo to highlight its importance for Asia, said Pamela Cox, World Bank vice president for the East Asia and Pacific region.

Despite the focus on Asia, the report pulls together lessons on both flood causes and mitigation options from around the world. For example, deforestation upriver from cities and loss of wetlands can exacerbate the effects of heavy rains. Jha said that if more of coastal Louisiana's wetlands had been preserved, the Hurricane Katrina storm surge might have been 5 to 10 feet lower. He added that deforestation in northern Thailand was a major factor in last year's flooding in Bangkok.

Some urban areas are worsening their predicament by overusing groundwater, which often causes subsidence. Meanwhile, paving and development associated with urban growth increases rain runoff and hinders groundwater replenishment. And rapid urbanization often results in shantytowns near riverbanks and marshes. When flooding occurs, "it's often the poor, especially women and children, who are most directly affected," Cox said. The dark cloud over all of this is global warming, which could produce more extreme weather events, the report notes.

Just as there is typically no one single cause to an individual flood, there is no one-size-fits-all solution to preventing or limiting their damage. "Each flood is different," Jha said. Mitigation requires integrating the efforts of a wide range of scientists, engineers, and social scientists to create flooding hazard maps to guide urban planning, develop watershed management strategies, deploy early warning systems, and plan for evacuations. The World Bank report concludes it makes sense to concentrate mitigation efforts on Asia because many countries are still at an early stage of urbanization. "There is an opportunity to build this sort of risk planning into urbanization, it's harder to do after the fact," Cox said. Jha added that the report's findings will guide World Bank support for development programs.