Urban Heat Islands

by Nicole Saad on April 13, 2014

As urban areas become more populated and developed, the landscape begins to change. Buildings, roads, and infrastructure replace land and vegetation. Moist surfaces become dry and impermeable to water. These environmental changes result in urban regions to be warmer. The urban regions create an “island” of high temperatures that can occur on both a surface and in the atmosphere. On a summer day, the sun can heat dry surfaces, such as pavement and roofs, to 50-90°F warmer than the air temperature. Heat islands are present during the day and night, but are stronger during the day when the sun is out. Atmospheric heat islands have an opposite effect on temperature than on surfaces. The urban heat islands in the atmosphere are most weak during the late morning and early afternoon until sunset. The atmospheric temperature is higher after sunset because of the release of temperature from the urban surfaces. Urban temperatures are lower along the borders of the city with less population and buildings. The addition of parks, residential areas, and bodies of water help in lower temperatures.urbanheatisland

Individuals who live in urban areas most likely expect warmer temperatures, but why is the concern for these urban heat islands so significant? Warmer temperatures, especially during hot summers, affect the urban environment and the quality of life among the urban population. Excess heat from hot pavement or rooftop surfaces is transferred into the storm water, which then drains into storm sewers and increases water temperatures. Although it might seem like a small effect, dramatic changes in temperature can cause stress to ecosystems. Higher temperatures also cause increased energy consumption. When temperature increases throughout the day in urban regions, there is a higher demand for air conditioning. A study performed by the EPA proves that the heat island effect causes 5-10% of peak electricity demand for air conditioning in buildings. There is an elevation in the emissions of air pollutant s and greenhouse gases from power plants. This is a result of an increased demand in energy. Not only does the urban heat islands affect the environment, but it also affects the people living in the urban areas. Both warm days and high levels of air pollution lead to health consequences. People in urban regions exposed to heat islands have general discomfort, respiratory difficulties, heat cramps, non-fatal heat stroke, and heat-related mortality. In order to prevent negative health outcomes, populations living in urban regions should be aware of urban heat islands and take action.

All efforts to reduce urban heat islands must be a voluntary effort by the people in these urban regions. The urban populations must increase the tree and vegetation, including green roofs, in the city to reduce the amount of surfaces exposed to the heat and sunlight. Benefits to trees and vegetation include greenhouse gas emission, removal of air pollutants, improved storm water control, reduced noise pollution, and creation of habitats. Creating cool pavements, which indirectly reduce energy consumption, air pollution, and greenhouse gas emission, can also reduce heat islands. The cool pavements are able to reduce noise, improve water quality, and enhance nighttime illumination. Although some of these changes may not be in the individual’s hands, it is important to be aware of the benefits and take action on the individual strategies.



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