By William S. Becker

With large swaths of the central U.S. spending Memorial Day weekend under water, it seems like a good time to write again about floods, folly and America’s love of bulldozers. It’s an old topic, but something is different this spring. Flood victims are not just flood victims anymore. Now, many of them are climate refugees.

A brilliant idea appears to be taking hold in the United States to protect lives and property from historic floods and rising seas. It’s called “get out of the way”. In other words, let’s move human development out of the paths of raging rivers and surging seas.

It may not be as far-fetched an idea as it seems. We are seeing signs of what will become much more disruptive trends in the United States: large numbers of domestic climate refugees retreating from floods as rivers and seas become increasingly dangerous because of climate change.

The evacuation of coastal and riverine disaster zones is not new, but it has not been common. Since the 1930s, official government policy has been to build structures in an effort to control inland and coastal flooding. We have spent billions of dollars on these structures. They have saved many lives, but they have cost some, too. Feeling a false sense of security, people moved into natural floodplains, assuming that structures made it safe. It turned out the assumption was wrong.

In the United States today, the average dam is more than a half-century old, beyond the age it was designed to last. Structures need to be maintained, but their owners have too often deferred maintenance because of other priorities. Most dams and levees were designed to hold back 100-year floods – those statistically likely to occur once in a century. But because of climate change, it is not uncommon for cities to experience 500- and even 1,000-year floods, so intense that they can overtop dams and levees, or cause structural failures.

Despite the emphasis on controlling rivers and waves, floods remain the nation’s most common weather-related disaster, and they are getting worse. Because science cannot tell us with precision how much rain will fall and where it will fall in the future, we can’t be sure how large urban floodplains are and will be.

This is not a small problem. A recent peer-reviewed study by the Nature Conservancy found that the federal government has vastly underestimated the number of Americans at risk of floods. In the lower 48 states, more than 40 million people, 13% of the population, are at risk along rivers – three times more than the official count by the Federal Emergency Management Administration.  Federal data predict that more than 60 million people will live in 100-year flood zones by mid-century.

The federal government says that 126 million people, 40% of the country’s total population, live in coastal counties. Forty percent of those Americans are in an “elevated coastal hazard risk category”. California, New York, Florida, New Jersey, and Texas have the largest number of coastal residents.

Some communities are taking things into their own hands, for example by setting building standards that exceed outdated federal guidelines based on past rather than projected floods.

The greater challenge, however, is the number of Americans who are becoming domestic climate refugees. From 2000 to 2010, for example, some parts of weather-damaged Louisiana saw their populations decline as much as 46%. It’s not just weather threats that motivate people to move; it’s also higher insurance rates and declining property values. Low-income families that cannot afford to move are left behind, creating pockets of poverty and risk.

How can communities avoid these risks? Job No. 1 is to reduce the intensity of floods, storm surges, and high-tide flooding by restoring beneficial ecosystems.  In watersheds, these range from upriver wetlands, reforestation, and conservation tillage, to more green spaces and permeable surfaces in cities so that rain is absorbed where it falls.

On the coasts, “non-structural” ecosystems include marshlands and wetlands, shoreline re-vegetation, beach restoration and the stabilization and conservation of dunes.

In parts of the United States, regions are actually restoring the natural features of rivers that were channelized in the past by the U.S. Army Corps of Engineers. They are putting the meander back, rehabilitating wetlands and creating space for floodwaters to spread out and slow down.

Job No. 2 is to create disaster avoidance and recovery plans based on the higher storm surges and greater river volumes expected as a result of climate change. The best way to manage these risks is to plan for worst-case scenarios. Much of climate science has focused so far on impacts at global, national and regional scales, but federal scientists are working to identify the impacts that localities can expect.

Getting out of the way is Job. No. 3. Louisiana may be the most recent example of a retreat from seashores and river banks. It has the unfortunate distinction of being America’s most flood-prone state. It has developed a 50-year, $50 billion strategy to manage its coastline, and a plan titled LA SAFE that describes options for the residents of six disaster-prone parishes.

As more communities consider similar plans, as they should, some tips might be helpful.

First, to cultivate the greatest public support for a very disruptive disaster prevention strategy, the entire community should be involved in creating the plan. The job should not be left to the local “planning elite”.

Some U.S. communities have held design charettes – town meetings in which architects, flood-mitigation specialists and other experts are brought in to work with residents in defining a plan the community stands behind. The plan should include new building requirements, revised zoning and designated “receiver areas” where flood victims can rebuild locally, but out of reach of floods. It should show where vital infrastructure and services will be located. It should include an evacuation plan.

This planning should be done in advance of the next disaster and designed to take effect automatically when it occurs. It cannot be done well in the chaos after a major flood.

The plan should be based on the best available projections of local vulnerability, in other words, the worst-case floods, winds, sea levels and storm surges. And the plan should identify how evacuated flood zones will be used to retain value as parks or wildlife sanctuaries.

Next, the community should decide how recovery will be done. Again, one option is evacuation where people scatter to other places. A second option is relocation, which rebuilds neighborhoods in safe places within the community. This allows the community to retain its tax base and people to preserve social relationships.

Flood zone evacuation can be horizontal or vertical. After Hurricane Sandy, some coastal homeowners decided to raise their houses on stilts to avoid future storm surges. Another option is to elevate buildings on mounds of dirt, so they are well above anticipated future flood levels. The downside of that option is that families are cut off from the rest of the community during large floods.

What we may be witnessing today is the beginning of a nationwide retreat from riverbanks and beaches. Flood-free places will gain population, flood-prone places will lose, and others will figure out how to mitigate or adapt to flood risks in place.

It is unlikely we will completely abandon the use of dams, levees, and coastal structures. But these engineered works should no longer be the nation’s principal strategy for avoiding flood disasters. Climate change should encourage a paradigm shift in the United States: When people are in conflict with the environment, it often is best for people to change their behaviors. It will work out a lot better than trying to domesticate Mother Nature.