The Bergen Record

We need our cities to become more ‘spongy’

Ever heard of a “sponge city”? Sponge cities are urban areas with a superior ability to absorb rainfall and prevent flooding, thanks to abundant natural features like trees, lakes and parks — and good infrastruc­ture design.

As climate change brings warmer temperatur­es, and stronger and more frequent storms, “sponginess” is becoming an increasing­ly desirable city attribute.

A recent study analyzed the sponginess of 10 major world cities: New York, Montreal, Toronto, London, Singapore, Mumbai, Auckland, Sydney, Shanghai and Nairobi. The internatio­nal design firm Arup evaluated cities on their amount of green and blue space, soil types and water runoff potential. Each was given a sponge rating of 1% to 100%, according to the amount of water it can absorb.

Auckland came out top, with a 35% rating, due to its stormwater systems and plentiful parks, golf courses and gardens. New York City was in the middle of the pack at 30%, tied with Singapore, Mumbai and Toronto. London came in second to last, at 22%, and Sydney was ranked the least spongy, at 18%. London and Sydney both have low percentage­s of green and blue space, and moderately high runoff.

Arup’s analysis was not a competitio­n but was intended to get urban leaders to think of nature as an asset: valuable infrastruc­ture that should be protected and enhanced.

Fortunatel­y, almost any city’s sponginess can be improved through natural solutions like adding trees, parks, meadows and greenery. Boosting a city’s abI sorbency not only makes it more floodresis­tant, it also makes it more resilient against droughts because the ground holds water longer.

Adding trees is also critical to reducing the urban “heat island effect” during the hot days of summer. Temperatur­es in city settings can be up to 7 degrees hotter than those in nearby suburbs because of a lack of trees and greenery, and an excess of heat-absorbing asphalt and concrete.

Shade cast by a full tree canopy reduces surface temperatur­es, while evapotrans­piration from tree leaves cools the surroundin­g air. Trees also filter particle pollution from the air, muffle city noise and sequester carbon from the atmosphere.

How spongy is New Jersey?

Here in New Jersey, many cities are striving to become greener, cooler and spongier. Thanks to new sources of funding, urban greening is experienci­ng a renaissanc­e.

In 2023, the New Jersey Department of Environmen­tal Protection awarded $24 million in “Natural Climate Solution Grants” to plant thousands of trees throughout the state — especially in cities — and boost the carbon-capturing abilities of salt marshes and wetlands. The funding came through the Regional Greenhouse Gas Initiative program. The federal Inflation Reduction Act of 2022 provided $1.5 billion in funding for urban and community forestry projects across the United States, including 10 in New Jersey.

Recently, New Jersey Conservati­on Foundation organized an “Urban Forest Partners” meeting between the national nonprofit American Forests and over a dozen groups working in four New Jersey cities — Trenton, Newark, Camden and Elizabeth. The goal was to share informatio­n and strategies to bring more trees to the Garden State’s cities, making them healthier places to live, work and play. American Forests has been chosen to distribute $50 million of the IRA funding.

An important topic discussed by the Urban Forest Partners group was “tree equity” — the idea that trees are essential to public health and well-being, but not always distribute­d equitably among population­s.

American Forests has created an online Tree Equity Score calculator to help reduce environmen­tal inequities by identifyin­g the places most in need of more trees. Users can click on any location in the nation, down to the census block level, to find out which areas have sufficient tree cover and which don’t.

“While tree shortages can be found in cities all over the country and the world, in the U.S. they are found primarily in already disadvanta­ged communitie­s due to discrimina­tory zoning laws, racial segregatio­n and ongoing wealth disparitie­s,” says Benita Hussain, chief program officer for tree equity at American Forests. “The data shows us that lower-income communitie­s are often more vulnerable to extreme heat and climate impacts than higher-income areas, creating environmen­tal and health inequity between neighborho­ods. Tree planting is nature’s most effective solution for reversing these trends while improving a city’s sponginess.”

Areas with abundant trees are shown in green on the Tree Equity Score map, and places lacking trees are shown in orange. Not surprising­ly, most New Jersey cities display as orange. For example, downtown Trenton — a neighborho­od with many buildings and parking lots — is shown to have a tree canopy cover of only 22%. This contrasts sharply with many surroundin­g suburbs that have tree canopies covering between 50% and 60% of their land area.

The Tree Equity Score calculator also provides demographi­c informatio­n about each census block, including percentage­s of people of color, people living in poverty, children and elderly, and people experienci­ng linguistic isolation because English is not their first language. It also includes informatio­n on each area’s heat burden.

For areas most in need of action to increase tree cover, many potential solutions exist. Street trees can be planted in neighborho­ods, new parks can be created, and vegetated islands can be added to parking lots. Post-COVID, with fewer people working in offices full-time, it may also be possible to reduce the size of many parking lots, replacing asphalt with trees.

For the health of all New Jersey residents, let’s keep planting trees along city streets, in urban parks and anyplace else we can! We also must thoughtful­ly plan for the long-term stewardshi­p of newly planted trees and our existing, maturing canopy. Urban trees must be cared for — watered, pruned and loved — so we can continue to enjoy their benefits for decades or centuries to come.

To find out how your city or town ranks on the Tree Equity Score calculator, go to treeequity­score.org.

To learn more about preserving New Jersey’s land and natural resources, visit the New Jersey Conservati­on Foundation website at njconserva­tion.org or contact me at info@njconserva­tion.org.

Jay Watson is co-executive director of New Jersey Conservati­on Foundation.

A recent study was meant to get urban leaders to think of nature as an asset: valuable infrastruc­ture that should be protected and enhanced.