City Heat: Growing Our Way to a Sustainable Solution

Across the nation, gardeners are starting seeds for their spring and summer gardens. In cities, city gardeners are looking anywhere for space to grow: in containers, vertical spaces, alley ways and balconies. How can we turn the planting season into an opportunity to save energy, reduce our impact on city heat and create community?

Cities displace agricultural and forested lands as they grow. Washington D.C., for example, was surrounded by farms way back before 1900, but now those farms are buried beneath neighborhoods like Dupont Circle and Capitol Hill. That land use change impacts the amount of heat that moves into the atmosphere and contributes to what is known as the "urban heat island effect." The two charts below, borrowed from the First Assessment Report on Climate Change in Cities (ARC3), show a "before and after" look at what the city's impact is on local climate.

Heat can be emitted from the earth in two ways: evaporation, which doesn't increase temperature, and "sensible heat," which does increase temperature (think hot asphalt or a tin roof). That kind of heat causes urban heat islands (as you can see above, the sensible heat from a roof, in the right chart, is three times that of the daily mean). Globally, evaporation makes up the bulk of heat that is emitted into the atmosphere, but on an asphalt rooftop that changes, not only increasing sensible heat but also reducing evaporation. These changes have a large impact on precipitation and contributes to the urban heat island effect.

Natural landscapes can help mitigate the impact of a city's heat production through increased evaporation. Trees and plants help cool the city, which reduces the need for energy-hogging air conditioners while also providing valuable ecosystem services like reduced water runoff, filtration, and habitats for city critters. The American Society of Landscape Architects show how small parks can revitalize cities with a simple idea: retrofitting a parking lot. WATCH:

But others might argue they also provide delight. Take this St. Paul fire station that not only got LEED-certified in their last redesign, they got a garden on their roof. "They make great chili in the firehouse," says St. Paul's fire marshal, Steve Zaccard. This garden not only provides a valuable climate service by reducing the impervious, hot surface of their roof, they are growing food and building a community around the firehouse.

Sometimes delight is digging in the dirt. That's what these kids are learning about through an organization called Casey Trees. The trees they plant will help Casey Trees reach their goal of restoring the tree canopy of Washington, D.C. -- and they've been planting a lot. Over 8,000 new trees hit the city streets last year and the organization plans on adding the same amount for the next 20 years.

City planners like those in D.C. and Minneapolis are starting the mitigate the impacts of the asphalt and cement in our cities. Some people, like Gashaw Tahir, are making an impact in global ways. Tahir's Greenland Development Foundation is trying to plant 1 million trees in Ethiopia to combat desertification, making him "a real life Lorax."

Weigh in on these ideas and share your own on Planet Forward.