SCOTT DETROW, HOST:
When it comes to climate change, it's often cities at the leading edge of preparing for the future. So we're going to take a look now at Copenhagen, Denmark, a city where a single storm 14 years ago prompted it to make big changes. NPR's Central Europe correspondent Rob Schmitz joins us now to tell the rest of the story. Hey, Rob.
ROB SCHMITZ, BYLINE: Hey, Scott.
DETROW: So let's start with that storm. Five inches of rain sounds like a lot, but when you compare that to hurricanes, you know, here in the U.S., it does kind of pale in comparison.
SCHMITZ: Right.
DETROW: How did that amount of rain cause so much problems?
SCHMITZ: Yeah, there are a couple reasons for that. First off, for those who've been to Copenhagen, you know that, A, it is flat, and B, it is built along the Baltic Sea. It's an ancient port. So when it rains there, water doesn't really have anywhere to go because it's at sea level. Secondly, the rainstorm that hit the city on July 2, 2011, was not your normal storm.
DETROW: Yeah, the scientists you talked to called it a cloudburst. What exactly...
SCHMITZ: Right.
DETROW: ...Does that mean?
SCHMITZ: So in a normal thunderstorm, you've got strong winds moving up, and this circulation of air inside the clouds leads to sort of a towering peak at the top. And in a cloudburst, you have similar mechanics, but one key difference meteorologists told me is the temperature. It's warmer in the clouds that make up a cloudburst, and that, says Danish Meteorological Institutes' Mark Payne, is a result of a warming climate.
MARK PAYNE: As the Earth's climate warms, the air obviously becomes warmer, and warmer air can hold more water. And at the same time, this more water evaporates from the oceans and comes up into the atmosphere.
SCHMITZ: And Scott, Payne says for every degree Celsius of warming, the atmosphere holds 7% more water. And in a cloudburst event, you've got a big storm cloud heavy with water, and at some point, it just dumps that water over a tight space in a short period of time. So those 5 inches of rain that fell on Copenhagen in that 2011 storm fell within a few hours. And it flooded the city, causing sewer lines to rupture, filling the streets with raw sewage. It was a total mess.
DETROW: That does not sound good.
SCHMITZ: No.
DETROW: So going forward, Copenhagen cleans itself up, and it goes straight to work to make sure it would be better prepared. Tell us what they did.
SCHMITZ: Yeah, so a year later, Copenhagen approved a $1.3 billion public works project to complete 300 flood mitigation projects throughout the city over the next two decades.
DETROW: What are some of those projects?
SCHMITZ: So the first project is a series of seven tunnels that were dug under the city. I went down inside one of them as a crew was putting the finishing touches on it. This particular tunnel is nearly a mile long and 10 feet in diameter. It's designed to hold four Olympic swimming pools' worth of water. And in the event of a big storm, rainwater would be funneled into it, and then it would be pumped out of the tunnel into the sea.
DETROW: I'm picturing this - it's just kind of like a large storm drain with a pump.
SCHMITZ: That's right. And in addition to these tunnels, Copenhagen has also transformed 20 parks and green spaces in the city so that each of them can turn into big reservoirs in the event of a flood. The city did this by digging into these parks, creating soccer fields and play spaces that are sunken into the parks. In one of these parks I visited, they also built a 3-foot-high concrete wall around it, and the gates that allow people into the park automatically rise out of the ground, sealing the wall shut so that the park becomes, like, this massive lake when it floods. So these types of parks - they're called sponge parks - are now found throughout Copenhagen. And the largest project the city is building is a man-made island just off the coast to protect the city from an increasing number of storm surges that can also cause flooding.
DETROW: That is NPR's Rob Schmitz, with a view of what one city is doing as it prepares for a change in climate. Thank you so much.
SCHMITZ: Thank you.
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