A Trifecta of Hazards for New Orleans

News Jun 27, 2013 No Comments
From just east of New Orleans in St. Bernard parish you can see some of the rapidly disappearing wetlands that exist just beyond the city. (Photo/Chris Johnston)

From just east of New Orleans in St. Bernard parish you can see some of the rapidly disappearing wetlands that exist just beyond the city. (Photo/Chris Johnston)

Sea-level rise, increasing temperatures, and stronger hurricanes

Since Jean-Baptiste Le Moyne de Bienville founded the City of New Orleans in 1718, the water that surrounds the city has defined its very existence. With changes brought on by global warming that water also has the very real possibility of destroying it over the next 100 years.

Climate change is a reality and one of the most damaging effects of it in the United States for coastal cities like New Orleans, is sea-level rise. NASA data indicates that since 1993 global sea levels have risen at a rate of 3.16mm/yr., or about 2.4 inches in the last 20 years. According to a new report Louisiana should anticipate a 3.3-foot increase in the next 100 years.

 

 Sea level rise is not the only problem

New Orleans has another problem in addition to sea-level rise issue, a process called subsidence; it’s sinking into the ground. USGS data shows that in the next 100 years New Orleans will sink approximately 50 centimeters, or 19 inches. Areas of New Orleans that are presently 1.5 to 3 meters below sea level will be 2.5 to 4 meters below sea level by 2100.

Dr. Mark Kulp, professor of geology at the University of New Orleans, said, “[Subsidence] is something that affects deltas on a global basis. The Nile delta has subsidence problems, the Mekong delta, Yangtze delta, the list goes on and on and on.” Kulp continued, “We are unique somewhat, in the sense that, because of the clustering of a major metropolitan city right in the middle of the high subsidence.”

Planning for the eventual rise in the waters is further complicated by the fact that the increase isn’t uniform. For instance, at Grand Isle, La., about 50 miles south of New Orleans, NOAA data shows sea levels will rise at a rate of 9.24-mm/yr. and not the 3.16mm/yr. global rate.

 

The temperature is rising

The temperature of the planet is increasing and these increases are more in some area and less in others. As the earth warms, water expands. The warmer the water, the more sea-level rise there is local to that area.

From 1880 to 2010 the mean global surface temperature relative to the average temperature has been trending upward. By 2010 both the annual mean and the 5-year average were at a +0.6 Celsius, meaning the earth, as a whole, is a half a degree warmer. In 2012, global surface temperatures were the ninth warmest on record.

 

More and stronger hurricanes

Warmer waters mean more frequent and more destructive hurricanes. Dr. Kulp said, “Some of the predictions that are associated with climatic change are that there will be an increase in the, essentially the destructive intensity of hurricanes, and possibly even frequency of hurricanes.“

The major hurricane protection tool in the New Orleans area is a very large and complex levee protection system. Levee heights are often determined using historical storm surge data and then trying to factor in the probability that one storm in maybe 100 years would be able to top that levee.

When the levees break or get overtopped you end up with scenes like this one after Hurricane Katrina. (Photo/Chris Johnston)

When the levees break or get overtopped you end up with scenes like this one after Hurricane Katrina. (Photo/Chris Johnston)

Are levees enough

New Orleans is attempting to create a levee system that will protect it from a 500 year storm. According to Denise Reed, Ph.D., Chief Scientist for the Water Institute of the Gulf, the subsidence issue may complicate that. Reed said, “The city is surrounded by levees. Over time, because of subsidence, the elevation of those levees gets lower relative to the water level.” She continued, “If we want to keep the same level of protection associated with those levee systems, we have to keep putting dirt on them.” Dr. Reed makes clear that with sea-level rise this will be a continual process for the city.

Hurricane protection levee along the New Orleans lakefront (Photo/Chris Johnston)

Hurricane protection levee along the New Orleans lakefront (Photo/Chris Johnston)

According to the State of Louisiana damages from flooding due to storm surge and rain events average 2.4 billion dollars annually. If major improvements are not made to reverse coastal erosion and improve hurricane protection systems, by 2061 damages could be as high as 23.4 billion dollars annually.

 

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Christopher Johnston

Insatiably curious guy who finally found a career that appreciates that curiousness

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