Urban Forests Make Cities More Resilient to a Changing Climate

By Mary Catherine O’Connor, Outside Magazine

New York (October 31, 2012) – Hurricane Sandy has again put the spotlight on the need for cities to adapt to more frequent and severe weather events. While it may seem counter intuitive, one way to make cities more resilient is to foster large, healthy urban forests. Without trees, flooding can be worse as has been shown in cities lacking sufficient vegetation. Houston, Nashville, New Orleans, and Philadelphia are among U.S. cities that are reforesting to become more storm resistant.

The loss of life and property damage from Superstorm Sandy is still being tallied, but the catastrophe is pointing a spotlight on the need for cities to adapt to more frequent, severe storms (also referred to, in many scientific circles, as “climate change”).

Fortunately for all of us who like being outside, one way to make cities more resilient to these storms is to foster large, healthy urban forests.

Have you ever grabbed a low-lying branch of a large tree after a rainstorm and shook it in order to soak your friend or sister or whomever is standing under its canopy? Then you’re a jerk. But you’re also good at demonstrating the power of a single tree to retain rainwater. Over the course of a year, a single mature tree can intercept several thousands of gallons of stormwater that, in developed areas, could contribute to flooding or at least fall directly into often-overwhelmed sewage systems.

Yes, most post-storm images feature downed trees that snap power lines, but without trees flooding events would worsen, as cities that have become denuded over many decades have learned. Houston, Nashville, New Orleans, and Philadelphia are among the U.S. cities that are reforesting some of their most environmentally sensitive areas in an effort to become more resilient to storms.

“I’m seeing cities beginning to recognize that parks and green infrastructure play a dual role,” said Catherine Nagel, executive director of the City Parks Alliance.”They can serve to mitigate against storm events and also provide recreational opportunities.”

In 2010, Nashville was hit by 13 inches of rain over 36 hours—the biggest rainfall in its recorded history—that claimed 11 lives and cost $2 billion. In reaction, the city launched a flood control plan that includes a buy-out program to relocate homes in the most vulnerable areas and replace them with parkland.Houston is also cultivating its urban forest as a tool for easing the chronic flooding that plagues the city. Philadelphia is planting its way into compliance with storm-water regulations. Tree-planting is often paired with a transition to porous asphalt, which also absorbs stormwater.

The issue is not just the volume of water that storms bring, but also what that water carries: salt, oil, gasoline, hydraulic fluids, and a witches brew of other contaminants that could otherwise move directly into sewers (and, in overwhelmed combined sewage/wastewater systems, directly into streams, lakes or oceans).

This does not account for the other benefits of an urban tree canopy. Buildings shaded by trees require less energy to cool, and one tree can remove up to 26 pounds of carbon a year, the equivalent of 11,000 miles of car emissions.

Original article source: Outside Magazine, Urban Forests Make Cities More Resilient to a Changing Climate

Related Resources
The Importance of Trees in Hurricane Sandy
Don’t Blame Trees for Storm Damage, Manage Them Better
Was NStar’s tree-cutting plan proven right by Sandy?