Heatwaves like the one that hit the northeast of America in July are likely to be more commonplace in the future.
A new study from climate scientists at The City College of New York (CCNY) suggests that densely built urban environments like Manhattan are likely to suffer more frequent and more intense heatwaves in the future.
“Manhattan is subject to an urban heat island effect because its physical landscape is significantly different from the surrounding suburbs,” said Dr. Jorge Gonzalez, NOAA-CREST Professor of Mechanical Engineering in CCNY’s Grove School of Engineering. “This makes heat waves here more intense because Manhattan cannot cool off as readily as outlying areas.”
For example, during the first heatwave of July, CCNY’s City Meteorological Network (NYCMetNet) saw the overnight temperature 10 to 15 degrees Fahrenheit higher in Manhattan than in Long Island or in western New Jersey. This was in despite of similar temperatures in all areas during the day.
High temperatures do not dissipate as quickly in Manhattan as in other areas because of the large amount of stored energy contained in its massive buildings, Professor Gonzalez explained. “While surrounding suburban and green areas may perceive the same maximum temperatures, the built regions will perceive them for longer periods of time.”
Professor Gonzalez doesn’t just expect the heatwaves to intensify and multiply in existing urban heat islands, but that they will become more commonplace as the needs of human populations expand to create more built up areas like Manhattan.
“To mitigate these effects, landlords and policymakers should strive greening the cities with urban parks and vegetated roofs, and motivate construction and retrofits that are thermally light and reflective to the sun when possible,” he said.
Another research thrust is the role played by aerosols, which are fine particles of solids or liquids in the atmosphere. Urban areas tend to generate aerosols, and the resulting humidity could modify precipitation patterns by interacting with clouds and affecting the energy balance, Professor Gonzalez explained. “The presence of pollution could increase or diminish rainfall. It could change the frequency and severity of storms, as well.”
Split storms, like the ones that deluged some Long Island communities earlier this month while leaving neighboring villages dry, could also be a phenomenon influenced by cities. “Because of heat and aerosols, cities could play a role by acting as a barrier to storm fronts, resulting in very concentrated storms in scattered areas.”
Further complicating the matter is the fact that different aerosols can have complex indirect effects with respect to heating and cooling, said Dr. Mark Arend, a research associate with NYCMetNet. “It’s a very complex problem.”