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Urban Forests for Health and Safety

edmonton trees

By Sean O'Malley

Drought combined with erratic patterns of excessive rain—this seems to be the new normal for North American cities. 2012 was the worst drought on the continent in 50 years. Higher-intensity hurricanes and rainfall—like we saw with Hurricane Sandy—are increasing flooding, costing the US over $2 billion annually and putting increased pressure on our already stressed infrastructure. In addition to wreaking havoc to the landscape, these extreme weather cycles have dire impacts on the safety and health of residents. One of the ways these impacts can be managed is with a relatively simple and low-tech strategy—the urban forest.

Edmonton, Canada, has been in drought for more than 12 years and the city has lost more than 30,000 trees during this time—that's over 4,000 each year. But Edmonton is not alone in its struggle. Most cities in the United States and Canada are seeing a range of moderately to severely abnormal dryness. Yes, tree loss is unsightly. But beyond their aesthetic value, trees improve air quality. They reduce extreme heat. And trees reduce storm water runoff as well as the property-damaging erosion it causes. These qualities disappear along with the trees.

In 2006, the city of Edmonton opted to preempt public health and safety risks posed by these changing climate patterns with an ambitious Urban Forest Management Plan that both replenishes lost tree cover and fortifies the city's forest.

Finding a Solution to Both Drought and Flooding

As opposed to looking to complicated and costly unnatural solutions, cities can look to trees as their most effective natural barrier in protecting urban water supply during times of extreme weather conditions. To take on its chronic flooding during the '50s and '60s, Curitiba, Brazil, a city lauded by urbanists and policymakers alike as a model for sustainability, reorganized its urban landscape by relocating the favela residents in some of the most flood-prone areas and moving in trees instead.

In Curitiba and Edmonton, along with other cities that are pursuing "Million Trees" initiatives, including New York, Los Angeles, and Miami, local governments have caught on to the fact that investing in the urban forest and its role as collector and purifier of storm water is undoubtedly one of their best flood insurance options. Urban trees act as our most functional storm water filtration system, both absorbing and filtering it. In New York, street trees intercept 890.6 million gallons of storm water (an average of 1,525 gallons per tree) each year, providing over $35 million in value to the city.

Protection from Air Pollution and Extreme Heat

Climate change is leading to extreme temperatures on both sides, including frigid winters and scorching summers (those who subscribe to the Farmers' Almanac already anticipate this summer being the hottest one on record. In cities where the urban heat-island effect comes into play, the public health value of trees becomes more important than ever. One of the biggest yet underreported public health concerns in many urban settings are respiratory issues including asthma—which one in twelve Americans now suffers from, to a large degree due to pollutants and debris in the air. Boosting the urban tree canopy is one of the most effective ways cities can address rising temperatures, poor air quality, and the health problems that come with both.

According to the American Society of Landscape Architects:

Research shows significant short-term improvements in air quality in urban areas with 100 percent tree cover. There, trees can reduce hourly ozone by up to 15 percent, sulfur dioxide by 14 percent, and particulate matter by 13 percent. U.S. trees remove some 784,000 tons of pollution annually, providing $3.8 billion in value. Furthermore, a single large healthy tree can remove greater than 300 pounds of carbon dioxide from the atmosphere every year. In fact, New York City's urban forest alone removes 154,000 tons of CO2 annually. Through their leaves, trees also provide evaporative cooling, which increases air humidity. Shaded surfaces may be 20-45 degrees cooler, and evapotranspiration can reduce peak summer temperatures by 2-9 degrees.

How to Build Your City's Urban Forest

By now it should be pretty evident that trees have monetary and human health value above and beyond beautifying our cities. So what does an Urban Forest Management Plan look like in action? In Edmonton, the city is seeking to proactively address its drought and flooding woes by doubling its tree canopy—from 10 to 20 percent—through community involvement and tackling policy constraints. The city is engaging in activities including implementing a naturalization master plan, replacing molding and diseased trees with healthy new ones, and looking at strategies to improve soil quality and tree health in the city's downtown core. The city is also looping in the community to share responsibility for the urban forest through a public education and engagement program, teaching Edmonton residents about both tree maintenance and fire safety. This program addresses the challenge and opportunity of the urban forest in short, medium, and long-term capacities.

I, for one, look forward to seeing Edmonton's forest grow and more cities start to identify the solution to climate adaptation and public health in their trees.

Sean O'Malley is Managing Principal in SWA's Laguna Beach office:

For more information on Edmonton"s Urban Forest Management Plan:

For information on Curituba: