When you hear the word "infrastructure," you probably think about roads, bridges, and tunnels. But not all infrastructure is built by humans and machinery. The most critical types come from nature. Forests, for example, can prevent pollution from flowing into streams that supply communities with freshwater. Wetlands similarly filter runoff from storms, reducing pollution that would otherwise reach rivers, lakes, and oceans.
Instead of building costly water-treatment plants and dams to protect their citizens from water pollution, cities across the country are investing in green infrastructure. It's especially important to help defend against the droughts and floods made worse by our changing climate. From rain gardens to absorbent pavement, urban communities are proving that nature's toolkit can often provide the most innovative solutions.
1. Rainwater harvesting
Trillions of gallons of polluted stormwater can flow directly from dirty streets and parking lots into our waterways, which presents major health hazards for humans and wildlife. So instead of letting the water drip off a roof or down a drain, cities are collecting and storing it. Cisterns for large commercial buildings can hold hundreds of thousands of gallons of rainwater that can be used for irrigation, toilets, cleaning—even firefighting.
According to an NRDC analysis of eight U.S. cities, if a city could capture all the rain that falls each year, that bounty would meet 21 percent to 75 percent of its annual water needs. Even capturing a portion for reuse could make a huge difference.
2. Permeable pavement
Also known as porous pavement, this drainage system allows water to move through a sidewalk or parking lot's surface instead of running over it and down drains. Rain seeps into layers of rock and soil beneath the surface, where the water is then naturally filtered. Because this material comes in the form of concrete, asphalt, and pavers, it's a great solution for parking lots, driveways, and sidewalks.
Another boon: NRDC’s report “The Green Edge” found that parking lots constructed of permeable pavement can be cheaper to maintain than asphalt. For example, West Union, a town the state of Iowa that's designated a Green Pilot Community, is on track to save $2.5 million after converting its downtown streets and sidewalks to permeable pavement.
3. Green roofs
Aside from just looking cool, roofs covered in plants can absorb up to 80 percent of the rain that falls onto them. During the summer, city buildings with green roofs can also help keep the air cooler. Typical heat-trapping dark roofs create an urban heat island effect, making most cities two to ten degrees warmer than rural or suburban areas. Plants on top of a building mean more comfortable temperatures inside, too. A 2013 NRDC study showed that during the summer, a green roof in Southern California can reduce daily energy demand for cooling in a one-story building by more than 75 percent.
4. More trees
Planting trees is one of the simplest green infrastructure techniques. Their canopies reduce stormwater runoff by soaking up rainfall and improving how stormwater filters through the ground. When rain falls onto a tree canopy, the leaves and bark hold onto the water until it does one of two things: evaporates or drips down to the soil below, slowing the flow of water and reducing runoff. Rain that falls directly to the soil is absorbed by tree roots and later exits as water vapor through the leaves. The roots also help reload groundwater supplies and maintain flow in streams during droughts.
5. Rain gardens
Shallow, flat, and slightly lower than the ground, these gardens trap rainwater and allow its vegetation and soil to naturally filter out pollutants. Some studies have shown that rain gardens can absorb 30 percent more water than more conventional landscapes. These structures can be particularly useful right under a roof downspout or on a lawn prone to flooding. Urban planners love them because they're relatively cheap to build, easy to maintain, don't take up much space, and can still be beautiful. More and more cities—from Philadelphia to Madison, Wisconsin— are installing them in public spaces. Some places like Seattle even offers generous rebates to homeowners if they plant one of their own.