No matter who they are and where they're from, people worldwide are drawn to water. One of every four of us lives on an ocean coast; millions more live along rivers. There are economic, aesthetic, and even psychological benefits from living next to water, but there is also a constant risk that the water will turn destructive.

The risk is growing rapidly because four converging factors are creating the proverbial perfect storm. One is that our response to floods in the past has made them much more dangerous in the present. There is growing interest in the United States, and perhaps in other countries, too, in pulling back from shorelines and riversides, returning them to nature, and rebuilding in safer places. More about this later.

Our situation

According to the World Meteorological Organization (WMO), weather, climate, or water-related disaster has taken place every day on average over the last 50 years. The number of these disasters has grown fivefold over that period, the WMO says, and economic damages have averaged more than $200 million a day.

Nevertheless, people keep moving into the paths of raging and rising water. Researchers report that river and coastal flooding is the most frequent and damaging climate-related hazard. It causes billions of dollars in damages each year. Other research shows more than 255 million people were victims of floods between 2000 and 2015. Yet the number of people living in flood-prone places grew more than 34 percent from 2000 to 2018. It's happening on all continents except Antarctica, and it's likely to continue, rising faster than the general population with the expansion of coastal cities, especially in Asia and Africa. As a result, governments and at-risk cities will have to choose more effective ways to protect people and property from escalating flood disasters. The safest option is retreat—wherever possible, the deliberate relocation of people and infrastructure to safer places. Scientists in the United States have concluded the relocation of entire flood-prone communities is unavoidable. Global climate change is one reason. The others are aging flood-control structures, population shifts, and unaffordable costs.

Global climate change

Floods can occur anywhere it rains, but they are inevitable for people living near oceans and rivers. They are growing more frequent and destructive because of rising seas, stronger coastal storm surges, snowmelt, and heavy precipitation, all exacerbated by climate change. Many places are more vulnerable to floods because their land is subsiding under the weight of cities or because of freshwater withdrawals.

Flood-prone populations worldwide should understand that the weather disasters we see today are merely a prelude to what's coming as civilization keeps dumping greenhouse gases into the atmosphere. So, our responses must be long-term but begin now.

Fresh research shows coastal populations are subject to sea-level rise as much as four times faster than the global average expected by the Intergovernmental Panel on Climate Change (IPCC). A conservative estimate is sea levels will rise as much as 32 feet by 2100, even in the increasingly unlikely event the world limits global warming to 1.5 °C above preindustrial times, the aspirational goal of the Paris climate agreement. If global warming approaches 2 °C, at least 570 cities and 800 million people and will be in danger of rising seas and storm surges, along with more than $720 billion in property. Damages to ports and harbors alone may be as high as $112 billion annually, according to the United Nations. In addition, sea-level rise and bigger storm surges will profoundly impact the multi-trillion-dollar ocean economy.

Aging structures

During the last century, the world tried to reduce floods risks by controlling rivers and waves with dams, levees, seawalls, artificial channels, and other engineering projects. Besides flood control, governments and private interests built dams to generate electricity, store water, irrigate crops, and provide recreation. There reportedly are 60,000 large dams around the world today. Another 3,700 are planned or under construction.

In the United States, and undoubtedly in the rest of the world, too, people built below dams assuming they were safe, even when structures were not designed to save lives. Most flood-control dams were built to be reliable for about 50 years. The World Bank estimates 19,000 large dams are older than that today. The United Nations University (UNU) reports that by 2050, [most of humanity] (19,000%20large%20%5bdams%5d%20(https:/ will live below large dams (those higher than 49 feet) built in the 20th century and well beyond their design life.

Also, the typical flood-control dam was designed to handle 100-year floods, those with a chance of occurring in any given year. But much larger floods are becoming common.

Even discounting climate change, dams are inherently risky structures, experts say. They can fail because of poor design, inadequate maintenance, operator error, age, record rains, siltation in their impoundments, and even burrowing tree roots and rodents. For all these reasons, there has been a steep increase in the rate of dam failures over the last 15 years, UNU reports.

Repairing aging dams is expensive, not to mention the cost of upgrading them to handle today's weather. Researchers at Portland State University found it would cost $64 billion to rehabilitate all U.S. dams that need repair but much less expensive to remove them.

Population shifts

Experts predict there will be hundreds of millions of climate migrants in years to come, with 216 million moving to safer places in their own countries. Many are already moving because of heat, fires, drought, floods, and rising seas. However, today's biggest population shift is into, rather than out of, those places.

We would prevent a great deal of damage and suffering if the migration away from floodplains began now in a planned and orderly process. A new report from the World Bank concludes, "While internal climate migration may be a reality we cannot avoid, with the right action now it doesn't have to become a crisis…Depending on the world's collective actions taken today, the trajectory of internal climate migration in the next half-century could be reduced by as much as 80 percent—to 44 million people—by 2050."

In the United States, the idea of moving people out of floodplains was unthinkable in the past. Government policy was to control rivers and waves so people could live next to them if they wanted. But now, the relocation of property from floodplains and restrictions on real estate development in them is getting serious consideration by the federal government and many at-risk communities. One U.S. government study found that every dollar spent to move at-risk homes would save $6.50 in disaster costs.

Rising costs

The conflict between growing populations and extreme weather will greatly strain government spending. The World Resources Institute (WRI) estimates 147 million people annually will suffer from substantial coastal and river floods worldwide by 2030, double the number in 2010. Economic damages along coasts and rivers will grow to $700 billion annually by 2030, WRI says.

That spending will take resources away from other critical objectives, like meeting the UN's sustainable development goals or funding the world's transition to clean energy.

"Managed retreat" as it's called in the U.S., won't be practical or possible everywhere, but it should become the first-choice option in flood-prone places. It is the safest, most permanent, and least expensive strategy for disaster avoidance.

Where it can't be done, cities should focus on restoring ecosystems like mangroves, barrier islands, marshes, wetlands, and reefs and replacing impermeable with permeable surfaces (China calls this "sponge cities"). Urban forestry, revegetation, watershed restoration, and "do no harm" agreements with neighboring cities can help, too.

It should go without saying that adapting to floods cannot replace efforts to stop polluting the atmosphere with greenhouse gases. Climate change can make more areas of the planet literally uninhabitable for all species, including ours.

However, the message here is this: The structures we built in the past to control rivers and waves are increasingly likely to fail, causing much worse death and destruction than if they never existed. The best way to avoid flood catastrophes is to move people out of harm's way while preventing more from moving in.