The Urban Heat Island Effect, Explained

by ‐ Tags: green living, property management

If you’ve been in Boston with the Wego team over the past few weeks, I’ll bet you felt the heat like we did! This summer has been a hot one, breaking records across the globe. Temperatures have been steadily rising over the past decades, and this is especially true in urban areas because of the Urban Heat Island (UHI) effect.

What is the UHI effect? It’s a term used to explain the phenomenon where urban areas are hotter than surrounding rural areas, despite similar weather patterns. According to the EPA, urban areas are on average 1.8-5.4 °F hotter than the surrounding rural areas during the day, and that number can climb to over 22°F hotter at night. These numbers will only increase as global temperatures continue to rise! In the dead of a New England winter this may not sound so bad. However, in the summer months, the UHI effect can be a very uncomfortable, even harmful, phenomenon.

The UHI effect has negative environmental, economic, and health impacts. As temperatures rise, property managers or the tenants in their apartment buildings crank up the air conditioning. This short-term solution actually worsens UHI by increasing greenhouse gas emissions as a result ofhigh energy demand, as well as pumping pollutants into urban air. Additionally, the ever-rising use of air conditioning increases peak energy demand, placing strain on the electric grid as well as hitting tenants and building owners hard in their wallets.

What causes the Urban Heat Island effect? Urban environments tend to have more paved areas, reducing the amount of vegetation. Vegetation plays a big role in localized temperatures. Trees provide shade, reducing the amount of sunlight that reaches the surface, as well as absorb the sun’s radiation for photosynthesis. Vegetation is also important in retaining moisture in the environment, which evaporates and cools the surrounding air.

Lack of vegetation is not the only contributing factor to the UHI effect. The built environment, especially roofs and paved surfaces, play a large role in increased urban temperatures. Conventional asphalts and concretes comprise the majority of an urban landscape, and these materials absorb lots of energy in the form of heat, increasing surface temperatures to well over 120° F in the summer. Pavements also release a lot of heat at night, contributing to the higher nighttime average temperatures in urban areas. Similar to pavements, traditional rooftop materials absorb a lot of the sun’s energy, increasing the local air temperature as well as the building under the roof.

Along with increasing air pollution, contributing to global climate change, and increased utility bills, the UHI effect poses a serious threat to human health. Every year the length and intensity of heat waves send many to the hospital with heat-stress-related illnesses. The elderly are especially susceptible to the perils of rising temperatures.

What can be done to combat this, you ask? Building owners have a few options when it comes to retrofitting existing structures and properties:

1.     Increase drought-tolerant vegetation on your property, especially along paved areas

2.     Use more reflective pavement materials: the EPA offerthessuggestions

3.     Add Cool Roofs: Reflective metal roofs for steep-sloping structures, or a spray coating or single-ply material for low-sloping roofs

4.    Incorporate green roofs, like Chicago's City Hall

5.    Use smarter building materials, like these suggestions from our neighbors in Cambridge, MA

Retrofitting a building and increasing vegetation may have up-front costs, but there is a high potential for savings on future energy bills, especially the fees associated with peak energy demand: we’ve seen many building owners recoup the cost of retrofits or other improvements in just a few years. It’s good for the environment and your wallet when you combat the UHI effect.