“A Twenty-First-Century Catastrophe” - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 180

Hurricane Katrina, which devastated the coastal regions of Louisiana, Alabama, and
Mississippi in August 2005, killed 1,836 people and caused at least $150 billion worth of
damage —a figure that is still being tabulated and does not include the billions of dollars
in insurance payouts and court-awarded damages still being litigated.
Nearly half the world's population—some 3 billion people—live in coastal regions
vulnerable to the rising oceans, intensifying storm surges, and less obvious problems
such as saltwater pollution of aquifers. Rising waters are already a problem for low-lying
nations such as the Maldives, the Seychelles, Bangladesh, and Holland. The World Bank
estimates it will take $75 billion to $100 billion to build adequate flood defenses in de-
veloping countries. Rich countries—the ones largely responsible for pumping climate-
warming gases into the atmosphere—have been reluctant to fund flood protection in
poorer nations.
By 2025 , when the world's population will be around 8.5 billion, some 6 billion
people are expected to live in coastal zones. Predicting future sea-level rise is a murky
and inaccurate science, but the National Academy of Sciences (NAS) estimates seas will
rise by five to twenty-one inches by 2025, and by 2100, the NAS expects seas to rise from
two to eleven feet above current levels. At that point, rising waters will become a far
greater danger to humans than they are now.
The United States has a flawed flood-protection system. It relies on a mishmash of
federal, state, and local bureaucracies—a dysfunctional system notorious for political
turf wars, chronic underfinancing, and a lack of leadership. Moreover, certain
policies—such as the federal government's “hundred-year levee” design and its lood in-
surance program—have unintentionally provided a false sense of security and encour-
aged people to build on risky sites.
In erecting floodwalls, federal agencies, such as the US Army Corps of Engineers,
use a “hundred-year” design criterion to determine how big a levee should be. This does
not mean a flood will occur once every hundred years; it means there is a 1 percent
chance of the levee's being overtopped each year. (A levee is overtopped when high
waves wash over it and swamp the “protected” area behind the levee.) The risk of over-
topping increases with time, as levees weaken and subside. Yet, people who build be-
hind a hundred-year levee are not required to elevate their buildings, floodproof their
structures, or purchase flood insurance—and as a result, their property is susceptible to
flooding.
The levees ringing New Orleans were supposedly built to withstand a hundred-year
flood, but the wind and waves of Hurricane Katrina plowed right over, under, and
through them. Climate change will exacerbate the problem: a one-foot rise in ocean wa-