Torrential storms, even catastrophic deluges like the one that hit this week, may be nothing new for South Florida.
But climate change has made their impact worse.
Sea level rise has brought the water table closer to the surface, leaving less room for the ground to absorb rainwater. It rendered less effective the culverts that drain water from eastern neighborhoods into the ocean. It has threatened the operations of the broad canals that rely on gravity to drain water from western communities to the ocean.
Despite grandiose labels such as “100-year storm,” these deluges are likely to become more frequent, scientists say, for the simple reason that warmer temperatures cause more water to evaporate and form storm clouds.
“We have low-lying areas with inadequate drainage, designed well before today’s conditions, with higher groundwater tables and with higher rainfall intensity,” said Jennifer Jurado, chief resilience officer for Broward County. “And they’re taking a long time to drain.”
The South Florida water table has risen by about a foot in the last century, driven by rising sea level, she said.
With less storage space available, the rainwater went wherever it could, which this week meant streets, parking lots and a lot of other places where it was not welcome, including lawns and even houses. For miserable weeks like this one, with day after day of torrential rain, the ground ends up saturated, as useless for absorbing water as the surface of a parking lot.
“Now there’s no storage in the system, there’s nothing left,” Jurado said. “We just used it up with this event. And so you’ll see flooding occur much more quickly when the system is already supersaturated.”
Michael Sukop, professor in the Department of Earth and Environment of Florida International University, said the South Florida water table has risen at about the same rates as sea level.
The water table varies in its depth, he said, lying closer to the surface near the ocean in cities such as Hallandale Beach and Fort Lauderdale, and deeper underground in inland cities such as Pembroke Pines.
Over the past two days, he said, as South Florida residents have complained about their drains backing up, he suspects the underlying cause is a saturated water table.
“The water table under this type of rainfall event comes to the surface in certain areas,” he said. “And at that point, many of our drains just cannot be expected to work anymore. If the water table comes to the surface, it just cannot accept anything else. And I believe that’s what’s happening in a lot of these areas.”
“People worry about impermeable surfaces,” he said. “But the truth is when the water table comes to the surface, the entire surface becomes impermeable and no more can get in.”
In addition to all these issues of infrastructure and sea level rise, we’re just seeing more rain than in the past.
Annual rainfall has increased by about a fifth of an inch a year for the past century, according to the Environmental Protection Agency. NASA, which uses satellites to study global rain and snowfall, says rising temperatures will generally cause increased precipitation, although dry areas could see less and wet areas are likely to see more.
Wesley Brooks, a scientist who serves as chief resilience officer for Gov. Ron DeSantis, on Thursday dismissed any link of climate change to increased current rainfall. In a tweet, he wrote:
“To all the self-appointed Jr. Climatologists out there, the @IPCC_CH AR6 (a report by the Intergovernmental Panel on Climate Change) assessed that there is low confidence in the emergence of a climate change signal in heavy rainfall & pluvial flooding.”
The panel’s most recent report, posted online, lists among the prime hazards of climate change, “More intense and frequent extreme rainfall and associated flooding in many regions including coastal and other low-lying cities (medium to high confidence).”
Brooks pointed to charts on the report that said that while climate change was expected to increase rainfall in the future, scientists don’t expect to be able to see strong enough evidence to prove the connection until the next century.
The South Florida Water Management District, the region’s major flood-control agency, is working with the Army Corps of Engineers to assess and revamp a water-control system designed more than 70 years ago, the district said in a written statement.
A key point of vulnerability for Broward and Miami-Dade counties is the system of large canals that drain western communities. Relying on gravity to carry water to the ocean, they can’t function as designed when tides and sea-level rise raise the ocean to the point that water can’t flow east into the ocean.
“The study assesses which infrastructure is at the highest risk of impact from a changing climate and addresses flood vulnerabilities, by enhancing the capacity of the most vulnerable coastal water control structures and adjacent primary canals,” said a statement from the district, which is run by a board appointed by the governor.
Anticipating worse rainfall in the future, Broward County has begun toughening standards for infrastructure such as roads and parking lots, said Jurado, the Broward resilience officer. New standards will anticipate 20% more rainfall in the worst events, with these risks built into the design standards, she said.
“Unfortunately, the groundwater table will continue to rise,” she said. “And we will continue to see rainfall intensification like we are seeing now.”
This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.
