Climate Change

Updated Feb 19, 2013

From plants to pavement, Chicago officials are considering how to adapt. You should, too.
Climate shifts may well have long-term implications for landscape contractors as regions that used to be cooler overall slowly become warmer and more prone to droughts in between heavy-but-sporadic rains.

By Ken Wysocky

With apologies to Bob Dylan, the climate it is a-changin.’ And those shifts may well have long-term implications for landscape contractors as regions that used to be cooler overall slowly become warmer and more prone to droughts in between heavy-but-sporadic rains.

What should future-looking, big-picture-minded landscapers be thinking about? For answers, it’s instructive to look at Chicago, where city officials are proactively staking out new paradigms for landscaping and hardscaping projects in anticipation of dramatic climate shifts.

“At the end of the century, winters here could be more like those in Pittsburgh, Pennsylvania,” says Sean Wiedel, assistant commissioner, Chicago Department of Transportation (DOT). “Or, in the highest-emission scenario, winters here might be more like those in Baton Rouge, Louisiana.

By the end of this decade, the city of Chicago hopes to reduce the impact of “thermal islands” by boosting its total shade-producing tree cover over hard surfaces to 23 percent, up from an estimated 17 percent.

“We could experience 45 to 85 days a year with temperatures above 95 degrees (compared to less than 15 now), as well as 25 to 30 percent more snow and rain in winter and spring and drier summers and falls.”

Worst-case scenarios also include more extreme weather and longer periods of drought-like conditions in between heavy, intense rainfalls; these dry periods will, in turn, make many trees, shrubs and plants more susceptible to diseases. Moreover, water will be scarcer as evaporation rates increase and water from heavier, more severe rains run off before they can be absorbed and recharge water tables.

USDA hardiness zones have already shifted between half to one full zone in the past 30 years, according to Wiedel. The upshot: Chicago could be in Zone 6 by the year 2090, he says, noting it used to be on the border between Zones 4 and 5.

“While we don’t know all of the answers, we want to think about the questions when we make decisions about infrastructure and plantings for projects,” Wiedel says. “Our goal is to view everything through a climate-change lens.”

Some of the weapons city officials envision using in their global-warming-adaptation arsenal include:

• More use of permeable pavement in the city’s 13,000 alleys and other areas where they’re a viable alternative.

• Creating more vegetative rooftops to better absorb heavy precipitation and reduce energy use for air conditioning and heating.

• Replacing common trees like white oaks and ash with warm-weather lovers, such as swamp oaks and sweet gums.

• Reducing the effects of urban heat islands — created to a large degree by large areas of pavement — by planting more shade trees in these spots, which are identified through thermal satellite imaging.

• Planting drought-resistant vegetation in parkway bio-swales that absorb rainwater and filter out pollutants.

The strategies are part of the Chicago Climate Action Plan (, inspired by former Mayor Richard M. Daley, who strongly believed in raising Chicago’s profile as an eco-friendly big city. It was created after climatologists first developed climate forecasts by interpreting 100 years of temperatures and precipitation data gathered by Chicago weather stations.

Rainwater runoff from Chicago’s 1,900 miles — or 3,500 acres — of concrete public alleys could dramatically decrease with increased use of permeable

Also under development is a climate-ready checklist, a joint venture between the city, the Field Museum, Nature Conservancy and the University of Notre Dame, says Abigail Derby Lewis, a conservation ecologist at the Field Museum.

“The goal of the checklist is to help project managers take into account forecasted climate impacts and ensure the projects will be sustainable and cost-effective in the long term,” Derby Lewis says.

City officials are already implementing some of the plan’s strategies because they make sense regardless of how quickly climate change occurs. A good example is rebuilding public alleys with permeable pavers, which can immediately help decrease flooding and reduce the load on wastewater-treatment facilities. The city already has used permeable pavers to rebuild about 150 alleys; alleys and streets cover roughly 25 percent of the city.

The city also encourages rooftop vegetation, which reduces rainwater runoff and provides additional insulation that keeps buildings cooler in summer and warmer in winter, Wiedel says.

“We have to look at the long-term costs of each strategy and use the right technology in the right place,” Wiedel explains. “For example, in some alleys with heavy truck traffic, permeable pavers are not a good choice.”

Other strategies, such as eliminating certain tree species from city tree-planting lists, continue to undergo scrutiny.

“We haven’t yet added more Southern species to the list at this point because we’re still expecting harsh winters and other urban stressors,” Wiedel says.

In any case, the city cannot succeed on its own, he points out. Residents — and like-minded landscapers— will have to pitch in, too.

“We encourage residents to use green-infrastructure techniques on their properties, such as rain barrels,” Wiedel explains. “We offer rebates on rain barrels, native plants, select trees and compost bins. We can’t possibly do all of this just on city property. We need residents to do it on their properties, too.”

So far, the city’s action plan has been well received and non-controversial, Wiedel says. Most people seem to think that being proactive trumps a head-in-the-sand mentality.

“If we did nothing, and some of the worst-case scenarios occur … the impacts would be even more severe,” he notes.

And that’s something to consider when, as Dylan noted, that hard rain’s a-gonna fall.

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