New York City is continuously hitting records for heatwaves and high heat days. Urban parks are critical infrastructure for cooling cities. However, not all park land is the same, and the magnitude of cooling benefits to urban residents depends on maintenance and vegetation.
In the summer of 2022, the Natural Areas Conservancy, a partner of the Central Park Climate Lab, launched a nationwide study with their Forests in Cities Network to study the cooling benefits of urban forests. The Forest in Cities Network study focused on how degraded forests cool the air as compared to healthy, maintained forests. The Central Park Conservancy worked with the Natural Areas Conservancy to expand the study to Central Park and asked a slightly different question:
“What are the air temperature differences between different cover types within Central Park and street trees over the summer?”
Vegetation cover types are spatial areas based on the composition of the environment. For example, on the street, the environment is largely covered by pavement or asphalt, and trees are found singularly in tree pits. There are various cover types within parks, including maintained lawns with trees, native meadows, planted gardens, and wooded areas. Wooded areas have almost full canopy cover, a denser tree population, leaf litter, soil, and herbaceous plants. The vegetation composition of these landscapes influences the ecosystem services and the benefits humans derive from the living environment.
We placed sixteen air temperature sensors on street trees outside of Central Park, on trees within maintained lawns in the Park, in wooded areas within the Park, and in various other landscapes.
We found that on the warmest day this past summer, July 24, 2022, the Central Park woodlands were 10 degrees Fahrenheit cooler than sensors placed on street trees. Sensors placed on trees within open maintained lawns were 5 degrees Fahrenheit cooler than sensors placed on street trees. Preserving and maintaining vegetated park land and healthy woodlands and natural areas in our urban parks is important as we collectively face warming temperatures. Acting as our natural air-conditioners, our wooded areas and parks are proving to be important in cooling our city.
We also found that cooling benefits were greater at night. In cities, the urban heat island effect causes cities to retain more heat than rural landscapes at night. Trees release water vapor at night contributing to the cooling effect.
This was a pilot project for the Climate Lab. In the future, the Lab would like to increase sampling by including other parks within New York City and adding relative humidity.