To Stop Catastrophic Flooding, the World Needs a Lot More Levees

It’s time to start buildings walls.

According to a new study by researchers at Germany’s Climate Forum, it’s going to be very expensive to build dike systems (or levees, whatever you want to call them) to protect urban coastal areas from flooding associated with climate change. But it’s nothing compared to the alternative.

In a paper published in Proceedings of the National Academies of Sciences, Jochen Hinkel estimates that the annual cost of climate-associated flooding will hit trillions of dollars annually by the end of the century if nothing is done to address it. On the other hand, worldwide levee construction could be done for as little as $12 billion annually by 2100, a figure he says is “much smaller than the global cost of avoided damages.”

This all depends on how much sea levels rise, how rich the world is, and where people are living in 2100. But he estimates that as much as 4.6 percent of the global population will be flooded each year in 2100 if nothing is done. Building and maintaining levees would cost between $12 and $71 billion.

For the record, levees and sea walls are related, but different things. Levees are generally used to regulate water levels and redirect it elsewhere. They are often sloped, whereas sea walls are usually just giant vertical walls that are supposed to keep water out of cities.

Getting a citizenry onboard with building new levees, at least in the United States, is tough. Last summer, New York City mayor Michael Bloomberg proposed spending $20 billion to build a system of flood walls around much of lower Manhattan and a 20 foot levee around Staten Island, a plan he called “incredibly ambitious.” The proposal will need Congressional approval, which is difficult when 58 percent of Republican lawmakers don’t believe climate change is happening.

The United States has roughly 100,000 miles of levees found in all 50 states and Washington DC, many of them built in the 19th century to protect farmland. According to the Federal Emergency Management Agency, 43 percent of the nation’s population lives in a county with at least one levee protecting it. But as you'd expect with a system so old, it's in dire need of repair and expansion.

New Orleans’ levees famously broke during Hurricane Katrina, and much of the United States’ levee infrastructure is failing, according to the American Society of Civil Engineers. The levee system received a D- in the group’s 2013 report card.

“The reliability of these levees is unknown in many cases, and the country has yet to establish a National Levee Safety Program,” the group wrote. “Public safety remains at risk from these aging structures, and the cost to repair or rehabilitate these levees is roughly estimated to be $100 billion.”

Of course, sea level rise is definitely not a distinctly American problem. Hinkel notes that, globally, more people are moving towards the coast, and nearly 5 percent of the world's population would get flooded annually in his model's worst-case scenario. That’s unlikely to happen, he says, simply because we’re going to have to do something about the problem before it gets to that point. And right now, walls are probably the best thing we have.

“If we ignore the problem, then the damages will be significant, but if we adapt, it would be quite simple to protect our most densely populated cities,” he said.

Some cities have experimented with replanting protective mangrove forests or building out dunes, and Hinkel admits that ultimately we'll decide on several different solutions, but that either way, dikes are likely to play a big role.

Humans could simply consider moving further away from the coastline, but according to Hinkel, that probably goes against human nature.

“If you look at places like New York and Florida, people want to live at the beach or live on the waterfront,” he said. “In the short run, you can make a lot of profit building there, but long term, you’re going to have a lot of damage there.”