How Central Park Cools the (Urban Heat) Island of Manhattan

Manhattan is often defined by its matrix of busy streets, towering buildings, and (of course!) Central Park. In the summer, however, it’s also defined by its staggering heat. Luckily for New Yorkers, Central Park’s 18,000 trees and 843 acres of trails, lawns, and gardens offer some much-needed reprieve when the island of Manhattan turns into what’s called an “urban heat island.”

The urban heat island refers to an area of a city that faces much higher temperatures than its surrounding areas—creating an “island” of extreme heat. More concrete and less tree cover exacerbates this difference in temperature, which can vary by 16 degrees depending on location. This is because hard, impervious surfaces (like paved roadways and empty rooftops) absorb, magnify, and slowly release heat throughout the course of a day, creating a warming cycle on city streets.

The Pond July 2018

The lush, cool landscape of the Pond stands in stark contrast to the adjacent buildings and streets outside the Park.

Parks have their perks

That’s where Central Park comes in. The Park’s trees, acting like large, leafy umbrellas, have a profound cooling effect for those visiting the Park. As the summer sun shines down and heats up New York City, these trees create a literal buffer, called a tree canopy, that cools and shades our Park, absorbing extreme heat before it can do significant damage.

How exactly does this work? Through a process called transpiration, trees absorb rainwater through their roots, which is transported to their leaves and released as water vapor. The release of this vapor, as well as the shade that a tree’s leafy branches create, lowers the temperature of the surrounding air.

Not surprisingly, the four “coolest” areas in the City last summer were near large parks, including Brooklyn Bridge Park, Prospect Park, and Central Park. These green spaces are an oasis for New Yorkers, who faced the 10th hottest July on record last year. As the east coast continues to experience record heat waves this summer, Central Park’s tree canopy is integral to the health of New York City residents and wildlife.

Heat island thermal

This thermal photo, provided by Dr. Jeremy Hoffman of the Science Museum of Virginia, shows the impact that even one tree makes in cooling its surroundings. Brighter areas indicate hotter spots like sidewalks and roadways, and darker areas indicate cooler spots like tree cover and shrubbery.

A changing landscape

Dr. Jeremy Hoffman, Chief Scientist at the Science Museum of Virginia and leading expert on climate change and the urban heat island, has led multiple nationwide studies tracking heat across neighborhood lines that show just how essential green space is to the health of a city.

According to Dr. Hoffman, Central Park’s trees act as the City’s “natural air conditioning units” and have a lasting effect on the temperature and air quality within and surrounding the Park. This cooling effect that parks provide to cities is especially important as the planet experiences record heat. “The urban heat island effect is separate from, but intimately linked to, climate change,” Dr. Hoffman explains.

Passive Lawn

As temperatures rise in New York, visitors find cooler temperatures on the Park’s grounds. Surfaces like grass, shrubbery, and tree cover have a much more pronounced cooling effect than their concrete counterparts.

Climate change aside, urban areas are still warmer than rural areas, and certain parts of cities remain warmer than other areas of the same city. “The added factor of global warming,” Dr. Hoffman adds, “basically amplifies the urban heat island effect, including the duration of these heat extremes, how intense they are, and who they most effect.”

These compounding factors reiterate the importance of a well-maintained tree canopy here in the Park. “Maintaining and protecting the existing green spaces that we have is one of the most important steps in mitigating the urban heat island effect,” says Dr. Hoffman.

There’s a tree for that

As Central Park’s tree canopy works hard to keep us cool this summer, the Conservancy’s team of arborists works equally as hard to care for these trees. These professionals inspect, monitor, and maintain Central Park’s 18,000 trees to set them up for success, while also planting new trees to keep the Park's canopy growing.

Tree Care Manager Peter Haupt has been working with the Park’s trees for 10 years, building upon his breadth of knowledge about specific tree species and what factors most affect them. “The vast majority of the trees here in the Park are well-suited for urban conditions,” Haupt explains. “They are less sensitive to fluctuations in temperature and in weather, and many have evolved to tolerate extended periods of drought, as well as extensive wet periods.”

Tree Climbing Preparation

Conservancy arborists Peter Haupt and Will Vitagliano in their outdoor office, preparing to climb a tree for inspection.

This resilience bodes well not only for Central Park, but for all who enjoy its environmental benefits. With the urban heat island effect becoming more extreme each summer, the Park’s trees offer clean air, cooling shade, and a needed dose of calm to those who visit. Haupt and his team are happy to provide that space. “Taking care of the Park’s trees is very important to me, now more than ever,” he says. “I want to do my job successfully so that we can provide a respite and relief for everybody that wants to come and enjoy it.”

Thanks to Central Park’s trees and the arborists who care for them, when the City becomes a heat island, the Park becomes an oasis. Stay safe from extreme heat this summer by following the guidance of public health professionals, and if possible, by enjoying the shade in Central Park. You’ll be sure to notice the difference that the Park’s tree canopy makes.