Florida floods: How much rain has fallen and could it happen again?

Heavy rain has deluged parts of southern Florida, forcing the US National Weather Service to declare a flash flood emergency and triggering the total shutdown of Fort Lauderdale airport. Road, rail and air connections have been cut off and emergency services were working through the night to rescue people stranded by rising waters.

Meteorologists say the rainfall is likely to have smashed local records and to have been driven in part by escalating climate change.

Here’s what we know about what has happened and whether such events can be predicted.

How much rain has fallen in Florida?

Over 50 centimetres of rain fell on Fort Lauderdale in southern Florida in the space of just 6 hours on 12 April, according to the US National Weather Service, more than one-third of the city’s annual rainfall and equivalent to the annual rainfall of London.

The total rainfall over the day may well be even higher. A WeatherSTEM station at Fort Lauderdale airport showed that almost 66cm of rain fell at the station in the 24 hours up to 7am local time on 13 April.

The intense downpours come after days of wet weather in Florida, which is still supposed to be in its eight-month dry season where average rainfall is about 7.6cm per month.

Niklas Boers at the Potsdam Institute for Climate Impact Research in Germany says the extreme rain was a “very, very, highly unusual event to happen [for Florida], particularly in the dry season”.

Which areas have been affected by the rain in Florida?

The heavy rains quickly overwhelmed city drainage systems in the region, turning roads into rivers and flooding homes. Some 22,000 residents were without electricity at one point on 12 April.

The worst of the damage has been around Fort Lauderdale, where transport networks were effectively shut down. Fort Lauderdale airport has been closed since the afternoon of 12 April and will remain so until at least midday local time on 13 April. Meanwhile, South Florida’s high-speed commuter rail service Brightline is also shut down.

Some 330 schools across Broward County, which covers Fort Lauderdale and parts of Miami, were closed on 13 April due to the hazardous conditions.

Further showers and thunderstorms are forecast for 13 April, with an additional 5 to 10cm of rain possible, according to the US National Weather Service.

There is very little city officials can do to minimise disruption when huge rainstorms like this deluge a city, says Boers. “If you have very high amounts of water coming down in a very short space of time, then it’s very difficult for those water amounts to infiltrate the soil,” he says. “It’s the nightmare for climate impact adaptation planners, because there’s basically nothing you can do.”

How does so much rain fall in such a concentrated area?

The rain was caused by a collection of slow-moving thunderstorms that gathered over Florida on 12 April. Such extreme rainstorms are becoming increasingly common as the climate changes. In 2021, an intense rainstorm stalled over Germany and Belgium for two days, causing catastrophic flooding. China, Italy and New York have also experienced similar floods from extreme rainfall in recent years.

The increase in rainfall intensity is due to climate-induced rising temperatures, says Hayley Fowler at Newcastle University in the UK. Warmer atmospheres hold more moisture, increasing the frequency and intensity of storms. “The capacity to have those bigger downpours is there, in terms of increased ability of the atmosphere to hold moisture,” she says.

There is also some evidence to suggest that climate change is making storms more likely to “stall”, leading them to deposit their rain in concentrated areas, raising the risk of flash flooding.

Can we forecast these events?

The likelihood of extreme rainfall is one of the trickiest weather events for climate scientists and meteorologists to forecast. One problem is that climate models seem to underestimate the potential increased severity of rainfall as the climate warms.

Researchers modelling climate change’s impact on rainfall rely on the Clausius-Clapeyron equation, which calculates that every degree of warming in the atmosphere should result in a 7 per cent increase in the intensity of rainfall.

But recent extreme rainfall events seem to be releasing more water than that, says Fowler, suggesting that something is amiss with climate modelling in this area.

For example, a study in 2022 found that climate change increased rainfall during the hardest raining North Atlantic hurricane of 2020 by 11 per cent – almost twice what would be expected from the Clausius-Clapeyron equation.

“The sort of downpours that we are seeing seem to show much bigger changes than that [the Clausius-Clapeyron equation], potentially,” says Fowler. “So there’s something else going on that we are not able to capture in our weather forecast models or our climate models.”

Fowler is among teams of scientists now studying how to tweak climate models so they don’t underestimate the potential severity of future rainstorms. “I think we are missing something important,” she says.