The amount of rain that fell in six hours Tuesday surpassed the average amount of rain the region usually gets in July and August combined, meteorologists from the National Weather Service in St. Louis say.
Some parts of the region received more than a foot of rain in less than a day. The heavy rains caused flash flooding and stranded hundreds.
Scientists say there’s evidence those types of downpours could become more common as a result of climate change.
The storm was a severe singular event but also could be part of a trend, said Claire Masteller, an Earth and planetary sciences professor at Washington University in St. Louis.
“It was a big event, but that’s connected to climate, and that’s the integration of all of our weather events,” Masteller said. “In theory, as our climate warms, as we start getting more hot days, that warmer atmosphere can actually hold more water vapor.”
As the planet gets hotter, warmer air holds more water, which is released as heavier downpours.
“We are essentially supplying more fuel,” Masterller said. “When these rainstorms happen, there’s more water in the atmosphere, which falls as rain.”
The intensity of the rain was just as noteworthy as the amount that fell, National Weather Service meteorologist Lydia Jaja said.
“It’s definitely unusual to see this amount of rain in this short amount of time,” she said.
Tuesday’s storms kept sucking up moisture from surrounding air, Jaja said. Weather experts call such storms “training thunderstorms” because they keep moving over and dumping water on the same area for a long time, like train cars going over a track.
“We had so much moisture to draw from, it just kept on raining and raining and raining,” Jaja said. “Storms and showers kept developing along it and just moving over the same place all night long.”
Jaja says it’s difficult to tie a single rainstorm to climate change, which is shown through long-term trends.
But heavy rains like Tuesday morning's are becoming more common as the atmosphere gets warmer.
Data from the Environmental Protection Agency shows that in recent years, a larger percentage of rain has come from single-day storms.
On Tuesday, the St. Louis region received about 25% of the region’s total yearly rainfall in just 12 hours, according to the weather service.
Cities will need to pay more attention to improving and securing infrastructure including sewage pipes, roads and bridges that aren’t used to withstanding such heavy rains, Masteller said. Cities also need to make sure rivers and streams can handle increased volumes of water.
“It's just in the landscape itself, too,” Masteller said. “The rivers around here are organized to deal with the water, or to do the job of moving the water that they see on the regular. So even the natural systems that we have around here aren’t used to seeing an event that big, so they're not optimized to deal with an event that epic.”
That means people will likely see more apartments flooded as water overtakes streams during large-scale storms, she said.
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