Tuesday, March 27, 2012

Climate change could cause frequent flooding

From: Houma Today  By Nikki Buskey

Sea-level rise from global climate change could increase flooding problems for already vulnerable residents of Terrebonne and Lafourche parishes, according to a new report.

Terrebonne and Lafourche ranked as the most-populated parishes in Louisiana facing the highest risk from sea-level rise.

They came in behind Jefferson and Orleans parishes. Houma and Bayou Cane are also ranked among the most-populated and exposed cities.

The report, “Surging Seas,” is the first to analyze how sea-level rise caused by global warming is increasing risk from storm surges for communities throughout the coastal U.S. It is also the first to generate local and national estimates of what land, housing and population is in vulnerable low-lying areas and how sea-level rise will affect these communities over time.

Tidal records show that the sea rose 8 inches over the last century, and projections point to a steep acceleration.

Coastal Louisiana residents are already accustomed to dealing with regular floods. Lower Terrebonne residents have faced a flood every few years over the past decade.

But could we flood even more often? Even small amounts of sea-level rise make floods more common by adding to tides and storm surge, scientists say.

By 2030, many communities will see storm surges combine with sea-level rise to raise waters at least 4 feet above the local high-tide line.

About 35 percent of Terrebonne residents and 53 percent of Lafourche residents live below this level. About 15,000 homes in Terrebonne and 20,000 homes in Lafourche would be threatened by flooding with 4 feet of sea-level rise.

Louisiana is projected to face 19 inches of sea-level rise by 2050, according to the report. That would put a population of 1.4 million people at risk, including 634,000 people and 4.7 million acres of land.

About 113 cities along the coast will have at least half their populations at risk of serious flooding problems, the report says.

Currently, Louisiana residents face a 17 percent chance of suffering a flood so severe it might happen once in a century. With sea-level rise, that goes up to 20 percent.

“Sea-level rise is not some distant problem that we can just let our children deal with. The risks are imminent and serious,” lead author Ben Strauss said. “Just a small amount of sea-level rise, including what we may well see within the next 20 years, can turn yesterday’s manageable flood into tomorrow’s potential disaster. Global warming is already making coastal floods more common and damaging,” he said.

Nationwide, nearly 5 million U.S. residents live in 2.6 million homes on land below this level. More than 6 million people live on land below 5 feet; by 2050, the study projects that widespread areas will experience coastal floods exceeding this higher level.

In Terrebonne and Lafourche parishes, it’s not just major floods from storm surge that might become more frequent, said Denise Reed, a researcher with the University of New Orleans and a Montegut resident. But smaller floods, too.

“This really underscores the need to provide some kind of protection, for our area in particular,” Reed said. “It’s not just because we’re low-lying. There’s literally nothing between us and the Gulf of Mexico.”

Low-lying roads and yards in bayou communities go underwater once or twice a year now during tropical storms or during strong southeasterly winds.

If the school bus can’t get down to those homes for a couple of days a year, it’s OK, Reed said. But if those roads start going under more frequently and for longer stretches, “it’s something that really starts to impact your day-to-day life. What’s now a minor inconvenience will become a much, much more frequent event.”

Locals, who have been dealing with flooding for years, have already begun to respond to the increasing flood threat by elevating homes and building levees. But Terrebonne’s current levee project, Morganza-to-the-Gulf, will only be built up to about 10 feet high. Levees will have to be taller and stronger if residents want to keep living in low-lying areas, because sea-level rise, combined with coastal erosion, will make flooding higher and more frequent.

“Right now, we know that’s not even going to protect us from extreme events,” Reed said. “And in the future, that might not even protect us from lesser floods.”

Visit the report’s website, surgingseas.org (http://sealevel.climatecentral.org/ ), to check out a searchable, interactive online map that can zoom down to neighborhood level to see your flood risk. The site features statistics for how 3,000 coastal towns, cities, counties and states will be affected by a sea-level rise of up to 10 feet.

Nikki Buskey can be reached at 857-2205 or nicole.buskey@houmatoday.com.

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