South Florida’s Achilles’ heel

In the next 48 hours, one of the fiercest hurricanes ever recorded is expected to slam into South Florida. Hurricane Irma, which tore through the Caribbean as a Category 5, has slowed a bit as it heads toward Florida. It is now expected to make landfall as a Category 4 storm, bringing at least 130 mph winds and flooding the coast with up to 12 feet of storm surge from the ocean.

In some ways, South Florida is better prepared to handle a Category 4 hurricane than any other area in Irma’s path so far. Revamped building codes required all high-rise condos and structures built in the past decade in Miami-Dade and Broward counties to withstand at least 130 mph winds (or 156 mph winds for critical infrastructure). The US Virgin Islands and Puerto Rico, for example, only require new buildings to withstand 110 mph winds. Florida’s state and local governments also have efficient evacuation and sheltering systems in place. And most gas stations and hospitals are required to run generators in case of widespread power outages.

But South Florida has one vulnerability that city planners and government leaders haven’t come close to fixing: flooding. It doesn’t take a hurricane, or even a tropical storm, to leave a neighborhood submerged in water for days. All it takes is a summer storm, or a seasonal king tide. In June, for example, heavy rains flooded inland Broward County, closing a popular mall for three days.

There are several reasons why water keeps pooling in the southern tip of Florida. Sea levels are rising, South Florida was built on a marsh, and rapid development keeps shrinking the wetlands that can absorb and drain excessive rainwater. So there are few places for water to go when Miami and Fort Lauderdale are deluged. Because South Florida’s economy — and tax revenue — is so reliant on real estate development, politicians have done little to put the brakes on urban sprawl.

If this sounds familiar, it’s because these are some of the very same issues Houston faced when Hurricane Harvey dropped 50 inches of rain on it in late August. The coastal Texas city is also built on swampland and has undergone rapid urban development in the last 50 years.

Now South Floridians are bracing for a storm that’s much larger, has more destructive power, and will bring a higher storm surge than any hurricane they’ve seen before. In 1992, Hurricane Andrew leveled 65,000 homes and killed 65 people in Miami-Dade. But it’s Irma’s storm surge and rain, not wind, that’s expected to bring severe flooding and could take people’s lives and inflict the most damage to property.

Why South Florida is so vulnerable to Irma’s rain and storm surge

The Miami metro area is one of the densest in the country, and the vast majority of people live along the coast. It’s the most desirable, expensive real estate here that’s also the most at risk of flooding and hurricane damage. Everyone wants a condo on the beach, and property taxes are a major source of revenue for local governments. But local leaders have done little to restrict development on the coast, other than requiring builders to install windows and roofs that can withstand 130 mph winds.

“You basically have 6 million people sandwiched between the Atlantic and the Everglades. Flooding is a big issue,” said Steve Adams, director of urban resilience at the Institute for Sustainable Communities.

With this monster storm, a storm surge of up to 12 feet — caused by rising water pushed onshore by the force of the wind — could crash onto the South Florida coast in the coming days, according to Friday estimates from the National Hurricane Center. (Hurricane Katrina produced a record 27.8-foot storm surge in Mississippi.)

The city’s poorest neighborhoods, such as Liberty City, are on higher ground, so they may be better off after the storm. They are, however, potential targets of what has been dubbed “climate change gentrification.” As sea levels continue rising, investors will put a higher premium on real estate in Miami neighborhoods at higher elevations.

Based on what we know about Hurricane Irma’s size and intensity, the destruction is likely to be more expensive than Hurricane Andrew in 1992. The reinsurance firm Swiss Re released a report estimating that damage from a similar-sized storm could cost up to $100 billion. That’s more than double the cost of damage inflicted by Andrew, in today’s dollars.

The jump in cost is mostly from the coastal development boom in South Florida, so there are many more luxury waterfront condos in harm’s way. Miami-Dade’s population has grown 35 percent since Hurricane Andrew.

In the four counties under evacuation order from Irma (Miami-Dade, Monroe, Broward, and Palm Beach), 1.3 million homes are estimated to be in flood hazard zones, but only about 34 percent of them have flood insurance, according to an analysis by the Associated Press.

“That’s the hard dance,” says Tisha Holmes, a professor of urban planning at Florida State University. “We make a contract by the choices that we make. If we choose to live in hazardous areas, we are choosing the risk that goes along with that.”

South Florida is supposed to flood on a regular basis

The other most obvious reason South Florida can’t stay dry is because it was never meant to. More than a century ago, Miami-Dade and Broward counties were flat marshlands. Developers and the federal government, sensing the area’s tourism potential, drained thousands of square miles of wetlands to create Miami and Fort Lauderdale. Farmers, enticed by the longer, warmer growing season, drained the marsh too.

To put that in perspective: The Everglades once covered 4 million acres of South Florida. Now it covers less than half of that — about 1.5 million acres. So it’s no wonder that Miami and Fort Lauderdale are always flooding, because there is not enough marshland to absorb the subtropical rains. And engineers — despite enormous efforts — can’t seem to devise a system that eliminates the problem, especially after hurricanes as powerful as Irma.

Two moderate hurricanes that hit South Florida in 1947 led to severe flooding in the region — dumping nearly 100 inches of rain (Harvey, on the other hand, flooded Texas with 50 inches in some areas). The catastrophe became known as the Great South Florida Flood. This is how the Sun-Sentinel newspaper described it:

The impact of the deluge spurred the federal government into action. The US Army Corp. of Engineers dug more than 2,000 miles of canals and levees, and a regional flood-control agency was formed: the South Florida Water Management District. Now, when parts of South Florida are underwater, the agency can move the water from one canal to another, dumping the excess into the ocean or into Lake Okeechobee.

Coastal cities in South Florida are prone to flooding even on sunny days. It happens during the king tides, which are natural events when the Earth’s gravitational forces push tides higher than normal, and ocean water often spills onto the streets. These types of floods have increased sharply in recent years along the East Coast.

How sea-level rise has heightened the risk of flooding

Despite South Florida’s complex flood-control strategy, this system is still overwhelmed. That has a lot to do with rising sea levels, says Adams. In the past 25 years, the ocean has risen 3 inches in South Florida, and the higher tides are eating into the shoreline (most scientists believe the sea level is rising because of climate change). South Florida water managers sometimes can’t discharge rainwater into the ocean because the tide is so high that seawater is pushing into the water system.

“They have to shut the [ocean water] gates, and that means the streets stay flooded,” says Adams, who has been working with the four southeastern counties in Florida to come up with a plan to deal with the realities of climate change.

The flood-control system can barely handle regular thunderstorms. And it’s no match for a storm like Irma, which is expected to bring a storm surge of up to 12 feet on the South Florida coast. Urban planners in Florida have accepted the fact that they might never find a perfect solution to the flooding problem. The best they can do is try to mitigate the impact and bounce back more quickly, says Holmes.

“Engaging with this kind of storm surge flooding is part of the nature of living in the coast and a lot of coastal cities,” she said. “We are trying to find ways to be more resilient.”

Sourse: vox.com