Rain came down fast and hard Wednesday night in Chicago, creating some hazardous situations not only for drivers, but for first responders who were busy rescuing people who were stuck in high waters.

The National Weather Service issued a flash flood warning at 9:46 p.m. Tuesday night for Chicago and Cicero and the situation quickly escalated.

More than a month's worth of rain fell on Chicago in 90 minutes on Tuesday evening, according to the National Weather Service (NWS). "There were numerous reports of flooded viaducts, several reports of water rescues, and a few reports of flooded basements," the NWS said.

Chicago flash flooding caused sudden road washouts, and water rescues had to be made at more than one location on the West Side.

In parts of Chicago, flash flood alerts rang Tuesday, warning of dangerous conditions as cars were stranded and submerged on highways and water rescues were conducted, but how much rain actually fell across the region and how fast did it all happen?

Texas. North Carolina. Illinois. New Mexico. Flash flooding has surged into the spotlight in the last week with record-breaking flood events occurring nearly back-to-back across the country. Here’s why they happened now and why floods are becoming more intense.

Straighter, smoother streams flow more violently than those that meander due to a reduction in friction. Areas with steeper terrain can see water accelerate downhill at a much faster rate causing a more destructive flash flood than flatter, open areas.

Heavy rainfall fell on Chicago's West Side during a short amount of time Tuesday night, leaving some drivers flooded out in underpasses and several homeowners in ankle-deep water in their basements. A Flash Flood Warning was in effect for several hours before the water receded by early Wednesday morning.