Changing Planet

Five Years After Katrina, An Important Lesson Goes Unlearned

It’s getting harder and harder to blame Mother Nature for the disasters that befall humanity. While hurricanes, floods, droughts and storm surges are natural events, to be sure, the degree of disaster that unfolds when such events strike is often now heavily influenced by human activities.

When Hurricane Katrina smacked the Gulf Coast in August 2005, the protection from powerful storm surges provided by coastal wetlands and barrier islands had gradually been whittled away. Since the 1930s, Louisiana had lost 1.2 million acres of coastal wetlands. More than two dozen dams and thousands of miles of levees on the Mississippi River had trapped sediment that otherwise would have replenished them. At the same time, wetlands were drained and filled to enable oil and commercial development in the Gulf region. Even as the Army Corps of Engineers failed to adequately maintain levees to keep the floodwaters at bay, this loss of natural protection worsened the catastrophe.

The disintegration of the Chandeleur Islands, Louisiana


Similarly, there is a human hand in the devastating floods now ravaging villages and farmlands in Pakistan’s Indus River valley. Torrential monsoon rains are of course the proximate cause of this disaster, but river engineering plays into its severity and extent. The Indus emerges from the Himalayas carrying millions of tons of sediment from the young, eroding mountain chain. Under natural conditions, the river would carry most of that nutrient-rich load across a gently sloping sandy plain to its delta adjoining the Arabian Sea, helping sustain mangrove forests and fisheries there.

(See pictures of the floods in Pakistan.)

But today the vast majority of the river’s water is diverted into irrigation canals, leaving too little flow in the main channel to transport the sediment. As the silt settles out, the capacity of the channel to contain flood flows decreases. With little active floodplain left to absorb flows overtopping the banks, the result is catastrophic flooding – in this case covering one-fifth of the country and forcing 20 million people from their homes.

And on December 26, 2004, the tsunami that struck coastal Asian nations and claimed some 273,000 lives cast a spotlight on another valuable service performed by intact ecosystems–the storm and wave protection provided by mangroves and coral reefs. The tangled roots and dense vegetation of mangroves, which thrive where salt water meets fresh water, act like a shock absorber against storm and wave energy. Vast areas of these natural protective barriers had been cleared for hotels, shrimp farms, and other commercial developments, including half the coastal mangroves in Thailand.

These are extreme, but hardly isolated cases. Floods, droughts, storms and other weather-related natural disasters displaced 20 million people worldwide in 2008. According to Munich Re, the large German re-insurance company, some 850 weather-related disasters occurred in 2009, compared with an annual average of 770 over the previous decade. Economic losses from natural catastrophes in the ten years prior to Katrina exceeded the combined losses from 1950 through 1989.

With climate scientists warning of more extreme floods and droughts in the decades to come, the human and economic losses are bound to increase.

Certainly more people now live in harm’s way-along coastlines, on floodplains, and in deltas. But the hidden factor in many “natural” disasters is the loss or degradation of “ecological infrastructure.” Healthy rivers, floodplains, wetlands and forested watersheds provide services of enormous value to society just as roads, bridges and treatment plants do. They help mitigate floods and droughts, buffer storms, transport sediment, filter pollutants, purify drinking water, and deliver nutrients to coastal zones. In 2005 scientists participating in the Millennium Ecosystem Assessment estimated that wetlands alone provide services worth $200-940 billion per year.

Around the world, however, these services are rapidly disappearing. Some 25-55 percent of the world’s wetlands have been drained, 35 percent of global river flows are now intercepted by large dams and reservoirs, and more than 100 billion tons of nutrient-rich sediment that would otherwise have replenished floodplains, deltas, and coastal zones instead accumulates in reservoirs. Post-Katrina, the Gulf coast continues to lose a football field’s worth of wetlands every 38 minutes.

Just as we buy home insurance and life insurance to protect ourselves and our families from catastrophic losses, so society now needs to “buy” disaster insurance to reduce the damage caused by floods and other weather-related events. By strategically investing in the protection and restoration of ecological infrastructure, we can begin to re-gain the benefits of nature’s services.

Some nascent efforts in this direction have at least been floated. Within a month of the Asian tsunami, officials in Indonesia–where more than 126,000 of the tsunami deaths had occurred and where some 1.6 million acres of coastal mangroves had been lost in the preceding few decades–announced a large-scale effort to restore the nation’s mangrove defenses. In the aftermath of Katrina, U.S. scientists have been studying the idea of diverting Mississippi River water back toward Louisiana’s disappearing coastal swamps, to supply the nutrients and sediments needed to rebuild them.

Overall, however, the story is one of inertia, neglect and missed opportunity. After the Great Midwest Flood of 1993, U.S. researchers estimated that restoration of 13 million acres of wetlands in the upper portion of the Mississippi-Missouri watershed, at a cost of $2-3 billion, would have absorbed enough floodwater to have substantially reduced the $16 billion in flood damages from that event. But instead of calling floodplains and wetlands back into active duty, officials in the region permitted even more floodplain development. Nicholas Pinter of Southern Illinois University estimates that 28,000 new homes and 6,630 acres of commercial and industrial development have since sprung up on land that was under water in 1993.

Climatic change and its anticipated effects on the hydrological cycle will make the protective resilience of ecological infrastructure all that more critical and valuable. With the pace of “natural” disasters picking up, an international effort to shore up the planet’s natural defenses cannot begin too soon.



Sandra Postel is director of the Global Water Policy Project and lead water expert for National Geographic’s Freshwater Initiative.  She is the author of several acclaimed books, including the award-winning Last Oasis, a Pew Scholar in Conservation and the Environment, and one of the “Scientific American 50.”


[This post has been reformatted for Water Currents.]

Sandra Postel directs the independent Global Water Policy Project and lectures, writes, and consults on international water issues. She is also Freshwater Fellow of the National Geographic Society, and serves as lead water expert for the Society's freshwater initiative. Sandra is the author of several acclaimed books, including the award-winning Last Oasis, the basis for a PBS documentary. Her essay "Troubled Waters" was selected for Best American Science and Nature Writing. Sandra is a Pew Scholar in Conservation and the Environment, and has been named one of the "Scientific American 50" for her contributions to water policy.
  • Goswami Kumar Alok

    To keep up with the natural balance in the eco-system, it is only the human beings;who is responsible. But, felling of a large numbers of trees & clearing up of forests for large projects is an great negative factor for natural disbalance in the environment of the globe.

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