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

Heavy rain has deluged elements of southern Florida, forcing the US Nationwide Climate Service to declare a flash flood emergency and triggering the entire shutdown of Fort Lauderdale airport. Street, rail and air connections have been reduce off and emergency providers have been working by the evening to rescue individuals stranded by rising waters.

Meteorologists say the rainfall is prone to have smashed native information and to have been pushed partly by escalating local weather change.

Right here’s what we find out about what has occurred and whether or not such occasions might be predicted.

How a lot rain has fallen in Florida?

Over 50 centimetres of rain fell on Fort Lauderdale in southern Florida within the area of simply 6 hours on 12 April, in keeping with the US Nationwide Climate Service, greater than one-third of town’s annual rainfall and equal to the annual rainfall of London.

The full rainfall over the day could be even larger. A WeatherSTEM station at Fort Lauderdale airport confirmed that nearly 66cm of rain fell on the station within the 24 hours as much as 7am native time on 13 April.

The extraordinary downpours come after days of moist climate in Florida, which continues to be presupposed to be in its eight-month dry season the place common rainfall is about 7.6cm per 30 days.

Niklas Boers on the Potsdam Institute for Local weather Affect Analysis in Germany says the acute rain was a “very, very, extremely uncommon occasion to occur [for Florida], notably within the dry season”.

Which areas have been affected by the rain in Florida?

The heavy rains shortly overwhelmed metropolis drainage techniques within the area, turning roads into rivers and flooding houses. Some 22,000 residents have been with out electrical energy at one level on 12 April.

The worst of the injury has been round Fort Lauderdale, the place transport networks have been successfully shut down. Fort Lauderdale airport has been closed because the afternoon of 12 April and can stay so till a minimum of noon native time on 13 April. In the meantime, South Florida’s high-speed commuter rail service Brightline can be shut down.

Some 330 colleges throughout Broward County, which covers Fort Lauderdale and elements of Miami, have been closed on 13 April because of the hazardous circumstances.

Additional showers and thunderstorms are forecast for 13 April, with a further 5 to 10cm of rain attainable, in keeping with the US Nationwide Climate Service.

There may be little or no metropolis officers can do to minimise disruption when large rainstorms like this deluge a city, says Boers. “When you’ve got very excessive quantities of water coming down in a really brief area of time, then it’s very troublesome for these water quantities to infiltrate the soil,” he says. “It’s the nightmare for local weather impression adaptation planners, as a result of there’s mainly nothing you are able to do.”

How does a lot rain fall in such a concentrated space?

The rain was attributable to a group of slow-moving thunderstorms that gathered over Florida on 12 April. Such excessive rainstorms have gotten more and more frequent because the local weather modifications. In 2021, an intense rainstorm stalled over Germany and Belgium for two days, inflicting catastrophic flooding. China, Italy and New York have additionally skilled comparable floods from excessive rainfall lately.

The rise in rainfall depth is because of climate-induced rising temperatures, says Hayley Fowler at Newcastle College within the UK. Hotter atmospheres maintain extra moisture, increasing the frequency and intensity of storms. “The capability to have these greater downpours is there, when it comes to elevated capacity of the environment to carry moisture,” she says.

There may be additionally some proof to counsel that local weather change is making storms extra prone to “stall”, main them to deposit their rain in concentrated areas, elevating the chance of flash flooding.

Can we forecast these occasions?

The probability of utmost rainfall is likely one of the trickiest climate occasions for local weather scientists and meteorologists to forecast. One drawback is that local weather fashions appear to underestimate the potential elevated severity of rainfall because the local weather warms.

Researchers modelling local weather change’s impression on rainfall depend on the Clausius-Clapeyron equation, which calculates that each diploma of warming within the environment ought to end in a 7 per cent improve within the depth of rainfall.

However latest extreme rainfall events appear to be releasing extra water than that, says Fowler, suggesting that one thing is amiss with climate modelling on this space.

For instance, a examine in 2022 discovered that climate change increased rainfall during the hardest raining North Atlantic hurricane of 2020 by 11 per cent – nearly twice what could be anticipated from the Clausius-Clapeyron equation.

“The kind of downpours that we’re seeing appear to indicate a lot greater modifications than that [the Clausius-Clapeyron equation], probably,” says Fowler. “So there’s one thing else happening that we aren’t capable of seize in our climate forecast fashions or our local weather fashions.”

Fowler is amongst groups of scientists now finding out how one can tweak local weather fashions in order that they don’t underestimate the potential severity of future rainstorms. “I believe we’re lacking one thing essential,” she says.