The Heat Island Effect

We are an urban area, so we start this part of the conversation with the basic knowledge that our temperature is hotter than our rural neighbors. All of the asphalt and concrete of our buildings and roadways absorb heat during the day and radiate that heat back into the atmosphere. This causes a “heat island effect” over our City. As our region has developed over time, so has the potential for rising temperature.

Fortunately, our proximity to the ocean and the breezes coming off the Gulfstream provide an antidote to this effect and keep our temperatures feeling manageable. It is the same reason why we feel cooler than people in elsewhere in the United States during the summer months.

The length of the hot season is also impacted by the heat island effect. A study several years ago at Florida State University’s Florida Climate Center showed that on average Florida’s hot seasons are now longer by one to three weeks, than they were in the middle of the last century. In Fort Lauderdale, the study indicated that our hot seasons are longer primarily due to ending later, in some cases by as much as three weeks later than historical records. This means that, rather than ending in November, our hot season is inching towards a December conclusion.

The significant dredging and development of the Everglades is a factor too. Our region’s natural ability to cool itself is compromised by any loss of plant life and natural waterways. Large scale efforts to restore the Everglades, and small scale efforts, such as ours to increase our Urban Canopy to from 20.6% in 2012 to 23.6% by 2018, will help in the long term.

Energy consumption is another huge driver of temperature. The heat island effect is exacerbated by increased energy consumption which usually produces increased greenhouse gas emissions. Our energy consumption is driven by growth. The more we build and the more we drive, the higher the emissions. A 2006 study showed that “differences between the temperature of a [weather] station in the heart of the city and one on its urban fringe often differed by as much as 14° F [in sampled Florida cities] and that “findings can be extrapolated to other Florida urban areas.” This was similar to the results of other large, southern Florida cities, and the study specifically notes that these cities “experienced rapid population growth since 1950.”

We should not overlook additional drivers of higher temperature. According to GISS: “…the sun’s irradiance, oscillations of sea surface temperature in the tropics, and changes in aerosol levels -- can also cause slight increases or decreases in the planet's temperature. Overall, [though] the evidence suggests that these effects are not enough to account for the global warming observed since 1880.”

While a variety of factors are causing our temperature changes, the data for urban areas like ours points to the heat island effect as the key driver of our longer season length and higher temperature. This data provides us with a clear path for addressing the challenge using effective methods for reducing the heat island effect. These include reducing paved surface area, utilizing lightly colored materials for paved surfaces, buildings and roofs, increasing the urban canopy and the ratio of green plantings, reducing carbon emissions from buildings by lowering energy consumption and installing more energy efficient appliances and fixtures, and reducing vehicular traffic and their carbon emissions by walking, biking, or using mass transit.

 

From sustainable development to transportation improvements, the City of Fort Lauderdale is taking a leadership role in helping our community to reduce our heat island effect. To learn more about what you can do, visit our High-Temperature Living pages. For more about the heat island effect, try these websites:

Department of Energy – Lawrence Berkley National Lab – Heat Island Group

The Heat Island Group at Lawrence Berkeley National Laboratory “works to cool buildings, cities, and the planet by making roofs, pavements, and cars cooler in the sun.”  Their website has easy to understand and useful information on making changes to your buildings and routines.  They also have an excellent primer on the heat island effect and why cities warm.

 

National Aeronautics and Space Administration (NASA) - Urban Heat Islands

NASA’s vision is “To reach for new heights and reveal the unknown so that what we do and learn will benefit all humankind.”  The agency is the primary provider of satellite data and images to assist agencies of all types in tracking and analyzing the changes happening to our Earth and atmosphere.  This section of their website provides videos, information and links to resources relevant to the topic of urban heat islands.

 

United States Environmental Protection Agency (US EPA) - Heat Islands

Resources provided by the EPA on this website include a compendium of mitigation strategies, a community action database, and regularly scheduled webcasts.  You can also get information about specific strategies to take depending upon where you live and can sign up for a specialized newsletter on the topic.  Of special interest is a 2014 report on how adaptation and mitigation measures can actually roll back warming effects.