Disaster-prone deltas next climate risk: ecologist

WASHINGTON (Reuters) - Some of the world's most productive and populous places -- river deltas from the Mekong to the Mississippi -- are ripe for disasters made worse by climate change, an ecological catastrophe expert said.

In fact, said marine biologist Deborah Brosnan, these disasters are already occurring.

Brosnan pointed to Myanmar's Irrawaddy Delta, ravaged by Cyclone Nargis in May. A couple centuries of human-generated transformation -- dams, rice paddies, the withdrawal of water -- combined with a dense, poor population and the effects of global warming created a triple threat, she said.

"We think something that's so vast, like the Irrawaddy Delta ... can't be vulnerable, when actually it's the other way around: something so vast is the most vulnerable," Brosnan said in a telephone interview from Oregon on Wednesday.

The Irrawaddy Delta stretches across 8.6 million acres with a pre-Nargis population of about 6 million. That kind of population density is bound to make disasters more deadly when they hit, said Brosnan, president of Sustainable Ecosystems Institute, an organization of scientists and others aimed at solving ecological problems.

Citing U.N. figures, she said 200 million people were affected by natural disasters in 2007, up 48 percent from 2006, and that "2007 was not necessarily considered a bad year."

Brosnan puts the Sacramento River Delta, including the San Francisco Bay Area, at the top of a short list of areas at high risk from long-term human transformation of the landscape, which could be accentuated by climate change.

Once a saltwater tidal marsh, the Sacramento Delta has been transformed into an agricultural plain and an essential source of California's fresh water supply. Farm fields, roads and some delta islands that lie below sea level are protected by 1,100 miles of levees.

She cited a recent study estimating a 66 percent chance of catastrophic failure of these levees in the next 50 years, which could result in floods and saltwater intrusion. Recovery costs could exceed $40 billion in this one delta, Brosnan said.

SEAS RISE, LAND SUBSIDES

Other delta regions at high risk from sea level rise and subsidence include the Mekong in Vietnam, the Chao Phraya in Thailand, and the Ganges-Brahmaputra in Bangladesh, the Yangtze in China, the Nile in Egypt and the Mississippi, along the U.S. Gulf Coast.

Historically, people have tended to settle in river deltas, for good reason: they're fertile and protected by wetlands from ocean storms. Wetlands also serve as spawning grounds and habitat for fish and other wildlife.

Over the last 200 years or so, humans have transformed these useful landscapes by draining the swamps and cutting down the mangrove trees and other plants that serve as "speed bumps" to slow down storm surges.

When humans drain water from wetlands, it can cause the land to subside, sometimes to below sea level, Brosnan said. At the same time, climate scientists predict global warming will cause sea levels to rise. Some researchers also believe climate change may cause more intense storms, though there is scientific disagreement on this point.

If the seas rise by about 3 feet (1 meter), the vast majority of the people who would be affected are those living on Asian river deltas, she said.

"The combination of ecologically weakened deltas and regular storms (whether more intense or not) means that millions are already vulnerable and unprepared," Brosnan said.

Even less intense storms could have severe effects because of the number of people now living in delta regions and the degradation of delta landscape, Brosnan said.

Because the risk is immediate, she said, policymakers need to factor in environmental repair in disaster-response plans.

Mitigating the effects on the environment would make it easier to protect people who live in the deltas, Brosnan said.

(For more information on the environment, see blogs.reuters.com/environment/)