What Is the Heat Island Effect?
On hot summer days, urban air can be up to 10F hotter than the surrounding countryside. Not to be confused with global climate change, scientists call this phenomenon the “heat island effect.” Heat islands form as cities replace natural land cover with pavement, buildings, and other infrastructure. Increased urban temperatures can affect public health, the environment, and the amount of energy that consumers use for summertime cooling. • Public Health: Heat islands can amplify extreme hot weather events, which can cause heat stroke and lead to physiological disruption, organ damage, and even death especially in vulnerable populations such as the elderly. • The Environment: Summertime heat islands increase energy demand for air conditioning, raising power plant emissions of harmful pollutants. Higher temperatures also accelerate the chemical reaction that produces ground-level ozone, or smog. This threatens public health, the environment, and for some communities may make it harder to m
The heat island effect, also referred to as the urban heat island effect, is an effect where the average temperature of an area is higher than nearby rural areas. The primary cause of the heat island effect is the conversion of space into an urban environment that absorbs more sunlight and stores it in large thermal masses. A secondary cause of the heat island effect is waste heat generated by massive uses of energy. The heat island effect has an impact not only on the city itself, but also on nearby areas downwind, which generally see between 10% and 30% more annual rainfall than areas upwind. There are a number of small factors that make up the heat island effect, and in aggregate they increase average temperatures substantially. The difference in urban temperatures over regional averages is seen most strikingly at night, and especially during the winter. One of the main causes of the increased temperature is that in an urban environment large buildings block out a great deal of the
Cities and urban areas are 3 to 8 °F (2 to 4°C) warmer than surrounding areas due to the heat island effect as shown in Fig. 1. This temperature difference is attributed to more buildings and pavements that have taken the place of trees and vegetation. Vegetation physically shades the ground, reducing surface temperatures. In addition, vegetation and trees cool the air and reduce ambient temperatures through transpiration (evaporating water through leaves). Research has shown the average temperature of Los Angeles has risen steadily over the past half century, and is now 6 to 7°F (3 to 4°C) warmer than 50 years ago(1).
