From green rooftops to rain gardens: Use urban space wisely

Thousands of acres of precious urban space remain unused or misused, when they could be enlisted in the struggle for climate health and biodiversity. It took a pandemic, but many Americans planting their first garden this year discovered a valuable resource sitting in their backyards: unused land. But old-fashioned lawns are not the only thing preventing productive land use. Look at satellite imagery of your city and you might see buildings with concrete roofs, parking lots, shingled houses, and wide roads covering most of the land. This land was once covered by trees, prairies, and wetlands. The displacement of nature without efficiently using the land has resulted in an unnecessary loss of habitat, more severe flooding, polluted waters, and the Urban Heat Island Effect. We can do better.

Minnesota is expected to have wetter weather as the climate changes. In natural settings, rainwater goes right into the ground, filtering its way into bodies of water above or below ground. In cities, the ground is often shielded by impermeable surfaces like concrete. This leads to flooding and a strain on municipal water management systems. The water flowing across these impermeable surfaces often picks up trash and pollutants along the way, depositing them in sewers, lakes, and waterways.

By replacing naturally draining land with concrete and buildings, we also limit the space available for plants and animals to live and find food. This includes humans. Despite the rich land available for growing food on the average single-family lot in the Twin Cities, we burn fuel by trucking most of our food in from outside the city, the state, or the country. We halt natural growth with chemicals and instead grow grass, which we keep short, polluting the air with petroleum-fueled mowers. The short, monoculture grass gives little food or shelter to animals and the whole system inhibits biodiversity.

As we leave fertile soil on valuable land unused, we also end up taking more land to house people. In turn, this leads to urban sprawl. Our rooftops collect sun and heat, but that sunlight goes unused for energy or plant life. Instead we place solar power installations on rural and undeveloped land that could be (un)used for other purposes.

Fortunately, just a few changes to our modern habits can help address all these problems simultaneously. Among them are green rooftops, green paving, rain gardens, fruit and vegetable gardens, and solar roofing. It is time for the bare roof and the well-manicured lawn of the 20th century to give way to a nature-friendly garden of the 21st century.

Green rooftops can be employed on sloped or flat roofs. As you may have seen on old Norwegian cottages, a sloped roof can support grass and other groundcover. This groundcover provides habitat and food sources for wildlife – such as birds and bees, who have seen rapid population drops. The plants absorb heat and cool the building better than shingle roofing, meaning better energy efficiency and cooler cities. Green roofs also filter and slow the flow of water, making floods less likely after a heavy rain. One more bonus: the plants on your roof convert CO₂ to oxygen.

On flat roofed buildings, there is also an opportunity for gardening, groundcover, or recreational areas such as the R.C. Knox Memorial Garden on the St. Paul Fire Department Headquarters. Flat roofs provide more opportunity for urban agriculture than the sloped roof of a house. As much as green roofs benefit flora and fauna, they can be good for humans too – even financially. Green roofs tend to cost more upfront than standard roofing, but they pay off long-term, extending the life of roofs and HVAC systems by insulating buildings from temperature changes. The space to grow flowers and foods right next to the people who would purchase them also makes it prime real estate for urban farmers.

A little more down to earth, drainage can be improved by installing rain gardens and replacing your driveway or patio with permeable pavers, green pavers (or grass pavers), or a ribbon driveway. These options can look more attractive than a traditional slab driveway, patio, or parking lot.

Individuals and property owners can choose to adopt these solutions, but cities should encourage good stewardship of the land by incentivizing them. Metropolitan Council recently launched the Surface with a Purpose project, similar to Google’s Project Sunroof, to demonstrate the resources over our heads. Still, upfront costs of green upgrades can be daunting for homeowners lacking resources to remodel. If your city does not incentivize green roofs, green pavement, or front-yard gardening and stormwater management, advocate for change. Ask your landlord about starting green projects at your building. Plant a rain garden. Make smart decisions about how we use this dear land. Threats to climate and biodiversity do not rest while we sit on these solutions.

Jack Stinogel is a dual-degree law and planning student (JD/MURP) at the University of Minnesota Law School and Humphrey School of Public Affairs. He holds a MSc. in applied linguistics from the University of Edinburgh, and wants to help cities mitigate and prepare for climate change.

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