Rain fell in sheets over parts of New England this week, triggering flash flood warnings in parts of eastern Massachusetts and Rhode Island.
The downpour turned a portion of I-195 West in East Providence into a river for hours on Tuesday, and some streets filled with water, too.
Wait, you might be thinking, aren’t we in a drought? If water levels are unusually low, why are we suddenly experiencing flooding?
Well, drought can actually make both rainfall and flash flooding more severe.
Scientists warn that climate change is increasing weather whiplash — rapid oscillations from one kind of extreme weather to another. That includes quick shifts from dry periods to wet.
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Rain occurs when the air reaches its capacity to hold water. When air gets hotter, its capacity to hold water increases, so it can hold onto it for longer, leading to drought. And when it finally does reach capacity, it has more water to drop, leading to heavier precipitation.
Data indicates that over the past several decades, drought has become more common in the region, even as Massachusetts has experienced more rainfall overall. The precipitation more often arrives in huge downpours instead of consistently over the course of a few weeks, experts say.
“We’re seeing either no rain or very heavy rains,” said Ellen L. Mecray, regional climate services director for the Eastern region at the National Oceanic and Atmospheric Administration. “When it rains, it comes down pretty strongly.”
Over the past few years, Mecray said, scientists have also found that New England has been experiencing weeks-long dry spells.
“We saw in 2016, and again these past few summers, that it seems to stop raining in June, and starts again in the Fall,” she said. “While we expect the region to be net-wet, as I like to say, there are definitely periods of dryness that we have to prepare for.”
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[5:10 pm] Torrential downpours this afternoon resulted in localized #flooding. One of the highest rainfall totals was in Rehoboth, MA where 7.01 inches was measured, all falling in just 3 hours, roughly 2 pm to 5 pm! #MAwx #RIwx #CTwx pic.twitter.com/ma5TcGBalT
— NWS Boston (@NWSBoston) August 23, 2022
Hot, dry periods also leave the ground parched. This can render soil hydrophobic, meaning it repels water instead of soaking it in.
“When heavy rain falls on these dried-out soils, most of the water tends to puddle or run off rather than soak in, leading to flash flooding,” said Jennifer Francis, an atmospheric scientist at the Woodwell Climate Research Center.
Other factors, like abundant pavement and other impervious surfaces, can also exacerbate flash floods, especially in urban areas.
“But in a more rural area, it’s definitely connected to the fact that the drought has essentially hardened the surface,” said Mecray.
A meteorology professor from the University of Reading in England illustrated this phenomenon in a viral video this month.
In this experiment Dr Rob Thompson of @UniRdg_Met shows just how long it takes water to soak into parched ground, illustrating why heavy rainfall after a #drought can be dangerous and might lead to flashfloods. @R0b1et @UniRdg_water pic.twitter.com/zbb3xLTXdK
— Uni of Reading (@UniofReading) August 10, 2022
It’s not just New England that’s experiencing this pattern. Experts say it’s also been at play in recent floods across Europe.
There’s much more of this in store for us in the future, especially if we don’t halt fossil fuel usage and curb planet-warming pollution.
“Whiplash events like these are expected to become more frequent and more disruptive as the Earth continues to warm under a thickening blanket of greenhouse gases,” said Francis.
Dharna Noor can be reached at dharna.noor@globe.com. Follow her on Twitter @dharnanoor.