It doesn’t take a hurricane to cause flooding in Miami anymore. In fact, it doesn’t even take a gust of wind.
“King tides” have been taking a toll on Miami for a number of years, and the phenomenon is only getting worse because of sea-level rise from human-induced climate change. A king tide is a higher -than-normal tide caused by specific alignments of the sun and moon.
Miami set daily high tide records for more than a week straight for the period bridging late July and early August, despite a total lack of storminess in the region.
Sunny day coastal flooding is now routine, submerging some areas on a monthly basis when the sun and moon line up just right. There’s even a “king tide season” in the late fall and early winter, when the flooding is particularly severe.
“Under a full or new moon, the tide becomes so elevated that combined with sea-level rise the water filters through the drains flooding the streets of downtown Miami,” Irene Sans, a meteorologist at WFTV in Central Florida, said in a Twitter message. The worst flooding occurs in September, October and November. Earth makes its closest pass to the sun in early January. That gravitational effect, coupled with the positioning of key weather systems in the fall, exacerbates king tide flooding during the autumn.
“These [king tides] happen several times a year, and they can really cause problems for residents. This is salt water mixed with sewage,” Sans said.
According to Capital Weather Gang contributor Brian McNoldy, recent king tides have rivaled some hurricanes when it comes to peak water levels.
Miami’s flooding has rapidly become routine. Since it happens beneath blue skies, many residents may overlook the dire warning signs mixed in with the waters. But while king tides are a natural phenomenon, the main reason they’re menacing Miami is because of climate change-related sea level rise. And as glaciers in Greenland, Antarctica and elsewhere continue to melt, adding water to already swelling seas, the 85,000 Miami residents who live below three feet above sea level need to start thinking about their futures.
I looked at tidal data from Virginia Key’s Biscayne Bay, on the Rickenbacker Causeway just a mile east of downtown Miami. The station reports water levels every six minutes. I analyzed a year’s worth of data from 1996 and did the same for 2018-19.
The zero mark refers to “mean higher high water,” a datum that denotes when flooding will begin. “That’s when coastal areas will start seeing flooding,” said Arlena Moses, a meteorologist at the National Weather Service in Miami. “We’re talking water above normally dry ground, so it’s a good metric to use.” So any time you see a data point above zero on these plots, it corresponds to flooding. The Weather Service lists “action” flood stage as being at one foot, minor flooding at 1.3 feet, moderate at 1.7, and major coastal flooding at 2.5 feet.
According to this analysis, there was a 5.9-inch sea-level rise in Miami since 1996. For a city that floods at just 16 inches above flood stage, that jump, which is due to both sea-level rise and land subsidence, is highly consequential.
You might think that should correspond to a 38 percent increase in the amount of flooding Miami is seeing now versus 23 years ago, since 5.9 inches is 38 percent of 16 inches. In reality, there has been a 3.2-fold increase in how often Miami sees nuisance flooding. That’s a 320 percent jump.
The reason? Flooding is nonlinear. That means that even if the sea level rose at a constant rate, the impacts and flooding Miami residents would experience skyrocket disproportionately fast.
Check out the graph. The blue shows a distribution of all measured water levels during 1996. The red shows the same thing over the past year. The jump to the right, and therefore higher water levels, is obvious.
But notice this: The yellow dashed line represents the threshold at which ordinarily dry ground becomes inundated. Though the distribution has shifted only six inches, since sea levels have risen six inches, look how much more red there is than blue above the flooding threshold. Even a subtle increase can have enormous effects.
During all of 1996, the gauge exceeded the 1-foot flood stage for only 5.4 hours. From July 2018 through July 2019, Miami spent 64.6 hours above 1 foot flood stage. That’s a roughly 12-fold increase in “action”-tier flooding. And this change happened in barely 23 years. The farther up the scale you go, the more that disparity grows.
A number of Miami neighborhoods are only a few feet above sea level. Grove Isle, an island neighborhood connected to Miami, sits three feet above sea level in spots. Coconut Grove isn’t much more protected.
Climate Central, a nonprofit organization specializing in communicating climate science, paints a grim picture for Miami’s future. They estimate that $5.7 billion in residential property value is at risk of being flooded by 2050 in just Miami Beach alone. Across all of Miami-Dade County, that figure looms closer to $8.7 billion.
In addition, an analysis by the nonprofit First Street Foundation found that from 2005 to 2017, Miami Beach alone has seen a loss of $337 million in real estate value related to sunny day flooding. The organization found that homes that are exposed to flooding increase their value more slowly than nearly identical homes on higher ground.
“The great ‘American Dream’ is definitely somewhere else,” lamented Sans, who says buying a home in South Florida is simply “not worth it.” That view is not shared by all home buyers, though, judging by home values that are still high in many areas.
“Some areas in the Keys no longer offer permits to build,” wrote Sans. “Parts of Miami are no longer offering long-term mortgages. Let’s say I buy along the coast — I have to deal with sunny day flooding. If I buy in the suburbs, then by the time I finish paying my mortgage off, I’ll likely be dealing with a serious flooding situation. Who’s going to buy my house then?”
Andrew Freedman contributed to this report.