- Flash floods are getting worse, due in large part to real estate development covering natural vegetation and replacing it with impervious surfaces such as concrete and asphalt.
- One historic town in Maryland is struggling to adapt to its wet new reality after two 1,000-year floods in a three-year period.
- "We have flood maps that were drawn based on predictions that are no longer true," one expert says.
On Memorial Day weekend, a catastrophic flash flood ripped through a town founded four years before the Declaration of Independence was signed.
Water crashed through walls, exploded through heavy doors and destroyed businesses up and down the once-kitschy Main Street in Ellicott City, Maryland. It would have been called a 1,000-year flood, had the same destructive deluge not crashed through town just two years earlier.
The first time, in 2016, on the city's nearly 2½-century-old Main Street, shop owners like Donna Sanger worked tirelessly to rebuild. It took months, but the city and the tourists came back.
"There was this enthusiasm. Let's build, let's put on a show, let's bring the town back, we're EC strong!" said Sanger, standing in front of her kitchen sundries store. But in 2018, the feeling is different.
"This is more like a funeral," she said.
Business owners now say they feel like these destructive floods are the new normal. This historic town of more than 65,000 residents, barely a blip on the map, is a blueprint for developing disaster — real estate development in the face of increasingly wet weather.
The overwhelming factor was intense rainstorms. "Climate change, due to warming oceans, changing atmospheric patterns, is increasing the intensity and the frequency of intense storms, making them wetter," said Joe Sexton, a scientist who uses satellite images to map changes in ecosystems.
Not only is more water falling, but more development is covering the natural vegetation and replacing it with impervious surfaces such as concrete and asphalt, along with rooftops through which water does not penetrate.
Ellicott City was built just north of the Patapsco River. Several tributaries above Main Street run through town to the river. Those water currents were the currency, the energy for the town, which was built around a mill in 1772. But since 1991, real estate around the popular main drag exploded. Developers submitted more than 100 plans to build residential and commercial buildings in about 3 square miles around Ellicott City. Most were approved, according to county records.
"We have flood maps that were drawn based on predictions that are no longer true," Sexton said.
In the most recent storm, nearly 8 inches of rain fell in just three hours — intense water with nowhere to go. Sexton's maps show how development increased the intensity of the flooding by up to 30 percent, and Ellicott City is just one example.
He mapped close to 8,000 square miles between Washington and Baltimore, and watched changes since 1984. The amount of land, or permeable dirt, that has been covered with impermeable streets, sidewalks and buildings is about equal to the size of the entire city of Baltimore.
Sexton said cities small and large, but particularly small-town America, where sewer systems are less advanced, are in danger. And it is not just the amount of water, as heavy rains cause tributaries to overflow, it is also the speed of that water, rushing through towns like a bulldozer. The only way to control that speed is to give the river new options of where to go. And that may be the answer in Ellicott City.
There are several proposals for reconstruction, but one leading idea is to level some of the historic buildings that stand by the side of the river and create a new river walk — a green space that could accommodate floodwater.
"We have to discuss whether or not the county should purchase some properties, how we can open up the stream," said Howard County Executive Allan Kittleman, whose jurisdiction includes Ellicott City. "We're not going to lose this town, but we need to realize, instead of imposing ourselves on the river, how can we coexist with the river?"
Kittleman, who led the area through both floods, said he is deeply committed to keeping Main Street standing, even if that means losing some of its beautiful, historic buildings, some of which were built in the late 1700s.
"I think we have to look at what's best for the town as a whole. We have to figure out what is the best way for us to save this town," he added.
One of those buildings houses Tom Shoemaker's family furniture business. He and his son barely escaped as the floodwaters surged through.
"The water kept coming up, and it started seeping through the doors.Then all of a sudden it just 'boom' broke the doors. And we were actually — my son and I — were here. We had got up here on the landing and able to get upstairs," said Shoemaker, who has lived in the area for nearly 50 years and leases space for his Main Street business.
After two dangerous and destructive floods, he will move his business uphill, losing the higher profile of the street, but gaining a sense of peace.
"Well, you got to do what you have to do, you know, because this seems like a reoccurring problem right now and being down here in the flood zone is not fun. ... It's difficult. It's horrible, yeah, it is," he said.
On the other hand, and the other side of the street, the change could benefit other businesses. Sanger owns the building that houses her business. She is invested in the town, and quickly began rebuilding her store.
"If we can get through this period of time, then it's a tremendous opportunity, too," Sanger said.
Because taking down the opposite buildings means her property would overlook a valuable new green space — a river walk, mitigating water and attracting business to her and her neighbors.
"There's a reason why they're over here working on these streets," she said. "They see the long picture, the long-term picture, and they know that if they hold on, they bring the buildings back, and the county does what we think they're going to do, that in the long run they're going to have very valuable real estate."
In the meantime, Howard County unanimously approved a one-year freeze on new development in the areas where stormwater runs into the river underneath Main Street. About 600 housing units in various stages of permitting would be put on hold, according to county estimates.
-- CNBC's Erica Posse and Lisa Rizzolo contributed to this report