NYC: An Island of Heat?

Summer is upon us and as the mercury in our thermometer begins to rise, some of us might be asking ourselves why is it that it feels much warmer in New York City than it does in surrounding suburban areas? Why are temperatures in the city remaining consistently warm even after the sun has set? One reason as to why we experience warmer temperatures throughout the day and higher-than-normal night-time temperatures in New York City, is due to a phenomenon known as the urban heat island (UHI) effect.

According to PlaNYC, cities can be up to 7°F warmer than surrounding areas. This is because urban infrastructure absorbs and retains more heat than suburban, green spaces, parks, and highly vegetated areas. This is also why the UHI effect is not consistent throughout all areas within NYC – air temperatures in areas with a larger percentage of artificial surfaces are greater than those in parks. This phenomenon can be observed in figure 1, an image provided by NASA, which portrays the surface temperature of New York City. If we assess the image closely, one can see that surface temperatures are higher in areas with more artificial surface and less vegetation. Figure 2 also portrays this affect.


Figure 1: Surface temperature of New York City. Provided by PlaNYC

Figure 2a and 2b: This figure shows the relationship between vegetation and surface temperature in New York City. Provided by NASA Earth Observatory


a) Vegetative Cover


b) Surface Temperature

Pavement, buildings, roofs, and other non-vegetated surfaces contribute to the effects of UHI due to the fact that these surfaces absorb the suns radiation at larger capacities than do vegetative or ‘lighter-colored’ surfaces. The reason why these surfaces absorb or retain more heat is, in part, due to the surfaces albedo. Albedo is a term that refers to how much an object or, in the case of NYC, land and infrastructure, reflects radiation from its surface; lightly colored surfaces reflect more sunlight whereas darker colored surfaces absorb more sunlight. For example, during the summertime, people wear lighter colored clothing in order to keep cool because lighter colors do not absorb as much heat; the same goes for everything else, ie., buildings, roofs and pavement. Another reason UHI occurs in NYC and other urban areas is because of low-levels of vegetation. Vegetation provides another cooling mechanism because it does not retain as much heat as artificial surfaces (roads, city sidewalks, etc.)

With rising temperatures regionally and nationally, the UHI effect is being amplified to unprecedented levels. This is a major concern for the city of New York for a number of reasons. As temperatures continue to rise and our climate continues to change, temperatures within our city are also skyrocketing and creating more opportunities for heat waves, which, in turn, creates public health issues (heat-induced diseases and related illnesses) and a need for more energy in order to stay cool.

According to Sustainable South Bronx’s report on UHI, public health is being affected by climate change and the UHI effect because warmer cities mean severe heat waves. Heat waves increase health risks for older-aged individuals and also those who are not well protected and prepared for extensive, excessive periods of heat. An increase in heat waves not only affects public health; the higher the temperatures, the greater the effect of UHI, the greater the need for us city-dwellers to stay cool. That means more air conditioning, more fans, and ultimately more energy usage.

Increased energy usage means increased amounts of emissions and pollutants into our atmosphere, which then contributes to furthering the increase in temperatures, and subsequently, energy. This self-perpetuating cycle can be slowed down and the affects this cycle has on our city and environment can be reduced. We, as New Yorkers, can combat UHI and cool down our city just by working within our local communities.

As a part of the PlaNYC report and its mission to build a greener, greater New York, there are many projects that are taking place all over the city to reduce the impact of climate change on our local communities and to create a healthier, cooler New York. Some of these projects include creating vegetative systems on roofs – ‘green roofs’, maintaining parks and ‘green spaces’, and participating in the NYC°CoolRoofs Program. Each of these projects not only reduces the UHI effect and greenhouse gas emissions, but also energy costs for buildings.

The time to act is now! Participate in greening NYC, and do your part for you and your local community. Lets all stay cool (pun intended).

By Mugzy Undemir, 2011 Human Impacts Institute Climate and Coalition Building Intern

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