The Louisiana coast in the year 2100, according to scientists' projections of rising seas and reduced sedimentation. Note that New Orleans is far off the coast. Photo courtesy of Science News, 7/18/09.
The residents of New Orleans have had it rough the last few years, following the devastation wrought by Hurricane Katrina. Much of the city has been restored and rebuilt, while other damaged areas still remain as they were after the storm. Unfortunately, due to the particular location of New Orleans, the situation may get worse instead of better in the coming decades. A recent study published in the journal Nature Geoscience predicts that ten percent of Louisiana will be submerged by the year 2100.
Scientist Harry Roberts of Louisiana State University and his colleague Michael D. Blum used computer modeling, based on scientific measurements, to estimate the effect of various factors on the gradual submersion of Louisiana. One factor is the sinking of land as sediments from the Mississippi River are compacted under their own weight. This compaction is a normal phenomenon. Historically, new sediments have been deposited at a rate that has replaced the sinking sediments, keeping delta land levels constant. But in the fairly recent past, the amount of sediment deposited by the river has been cut in half by dams upriver. Now, with the reduced flow of new sediments, the land is sinking at a net rate of about 8 millimeters per year. Near Baton Rouge, 150 km upstream, sediments are also sinking and not being replaced. The submersion process is just a bit slower upstream.
The lack of new sediment is not the only problem causing southern Louisiana to sink. The other issue is rising sea levels due to climate change. Scientists on the Intergovernmental Panel on Climate Change have reported that sea levels are currently rising at a rate of 3 millimeters per year, and that rate will accelerate as the climate continues to warm. Seas are expected to rise one meter between now and 2100, putting one in ten people across the globe at risk from coastal flooding.
By the year 2100, the combination of these two influences will submerge about 13,500 square kilometers in Louisiana, or 10% of the state's total area.
Even if more sediment-laden water could somehow be diverted to the sinking areas, scientists estimate that 12,600 square kilometers would still be submerged by 2100.
If the computer modeling is correct, New Orleans will be well away from Louisiana's mainland in just 90 years, and largely underwater.
New Orleans and southern Louisiana are not the only delta areas in trouble. Many of the world's largest and most densely populated and heavily farmed deltas are on their way to becoming open ocean. The causes are the same as those in Louisiana - reduction in the flow of sediment that restores and maintains deltas, and rising sea levels. Scientists James Syvitski and colleagues writing for Nature Geoscience estimate that the amount of delta surface area vulnerable to flooding and inundation will increase at least 50% this century, and more if the capture of sediments upstream continues.