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Thermal Islands: Cycle A

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1). Cities are warmer than surrounding countryside. Ait temperature in a city of one million people can be up to 3 decrees C warmer during the day and as much as 12 degrees C warmer at night.

2). Human influence has made cities warmer by adding buildings, impermeable surfaces, and concrete that both produce additional heat and trap heat in the urban environment.

3). Thermal islands have downstream effects. This frequently takes the form of increased convective weather activity like thunderstorms and rain showers.

4). Urban heat islands prolong the growing season in cities. This affect diminishes away from the urban center but can affect areas as far out as 2.4 times the size of the city itself.

5). The surface urban heat island can be very pronounced during the day when temperatures of exposed surfaces like roofs and pavements can be up to 50 degrees C (90 degrees F) warmer than the surrounding air.

6). The atmospheric urban heat island tends to be weak from late morning throughout the day. It intensifies at night as heat is released from buildings and surfaces.

7). Excessive heat events (heat waves) are enhanced in urban areas resulting in increased mortality and morbidity. In the U.S. over 1,800 deaths per year may be due to urban-enhanced excessive heat events

8). Evapotranspiration is the process by which water is moved from soil through plants then is evaporated into the air. The evaporation process removes heat from the air.

9). In urban areas, surfaces that were once permeable and moist are now impermeable and dry. This adds to the build up of heat in urban areas where usually 75% or more of the surface is impermeable,allowing for much reduced evapotranspiration.

10). Whenever water undergoes a change in phase, heat is either released or absorbed.
The latent heat of condensation is the amount of heat energy released when
water goes from the vapor to the liquid phase. Conversely, the latent heat of vaporization is the amount of heat absorbed from the environment when water evaporates.

11). The albedo of a surface is the percent of incoming solar radiation that is reflected from the surface. The albedo of the Earth-atmosphere system as a whole is about 30%.

12). Specific heat capacity is the amount of energy required to raise the temperature of 1 gram of a substance 1 degree Celsius. For water, it takes one calorie (4.18 joules). For air only about 0.25 caloties(~ 1 joule) is needed


Scenario: A heat wave in Chicago, increased thunderstorm activity in Quincy Illinois, and fogless London days and nights – is it possible these are all related to thermal islands? What is the role of cities in our climate – and more specifically, how does the urban heat island affect climate – not only in cities but in the surrounding countryside?

Numerous studies have shown how the concrete pavements and buildings retain heat in cities, making cities several degrees warmer than the surrounding countryside. The research of Tim Oke from the University of British Columbia has shown that cities of a million people can be 1 to 3 degrees Celsius warmer than the surrounding countryside during the day and as much as 12 degrees Celsius warmer at night.

Increased morbidity and mortality rates in cities during heat waves (sometimes referred to as Excessive Heat Events or EHEs) are exacerbated by the urban heat island effect. For this and other reasons, many believe mitigation of urban heat islands should be pursued. Some strategies being recommended include increasing trees and vegetation, and developing roofs that are green and/or cool.

As cities have grown, they have warmed. One result has been a decrease in fog. London, for example, used to be known for its "pea soup" fogs, but today, dense fog is rare in the city. New York, Tokyo and Los Angeles show similar trends. According to a November, 2005 article in Nature, changes in land cover in both cities and the countryside is responsible for part of the warming the United States has experienced in the past century.

In a 2003 paper in the Journal of Applied Meteorology , Rozoff, Cotton and Adegoke demonstrated how the urban heat island of St. Louis enhanced convective activity (thunderstorms) downstream of the city.

Not all the consequences of an urban heat island are negative. For example, savings in winter heating costs, less ice and snow, and longer growing seasons in urban areas are all positive results.


Author: Michael Witiw, Seattle Pacific University



Date: 1/22/2010


Scenario Images

Temperature profile in the vicinity of an urban heat island
This image shows how both nocturnal and daylight temperatures vary in the vicinity of an urban heat island, and the fact that they have a different magnitude, especially in the daytime. More... Image: Courtesy: EPA (modified after Voogt, J.A., 2002: Urban heat island, in Vol. 3, Encyclopedia of Global Environmental Change, Ed. Ted Munn, John Wiley & Sons, Ltd, Chichester, 660-666)

Contributors to thermal islands
Buildings, asphalt, concrete, and industry all contribute to the Urban Heat Island by their uptake and subsequent release of heat, and, in the case of industry, by adding heat to the atmosphere. More... Image: Courtesy NASA Earth Observatory



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Individual Assignment

Sphere Group Study

During this cycle you will become "experts" in the relationship of individual spheres. You will need to study the resources listed under readings, discuss your key ideas in your sphere group discussion space, and then submit your group's work for a grade.

Go to the course discussion space to find out which sphere you are studying during this module.

Read the scenario.


First, submit your individual questions and prior knowledge about this event and Earth system science to your sphere group discussion space. Then prepare a document about your prior knowledge and upload it to ESSEA.


  • Review the Individual Reflection Rubric.
  • Read the scenario.
  • Discuss your ideas about the effect of this event on your sphere in your sphere group discussion space.
  • Prepare and upload your prior knowledge reflection document to ESSEA.
  • Complete the individual reflection rubric.

Deadline: Friday, February 24 2017 11:59 PM (Eastern Time)
Upload Assignments
Team Assignment


  • Review the Group Sphere Study Rubric.
  • Describe your sphere in detail in the sphere group discussion space so you can share it with your Event Team next cycle. Refer to An Example of an ESS Analysis reading if you would like to review causal relationships.

Upload your group's most accurate analysis of the Sphere - Event interactions with reasoning and support to ESSEA and complete the rubric.
Deadline: Friday, March 3 2017 11:59 PM (Eastern Time)
Upload Assignments

Assessment is unavailable

Feeling the heat (Cycle A)
Students learn about the urban heat island effect by investigating which areas of their schoolyard have higher temperatures. Then they analyze data about how the number of heat waves in an urban area has increased over time with population.
Difficulty: beginner

Measuring Temperature Islands (Cycle A)
Goal is to identify both natural and urban heat islands and learn to use an infrared thermometer.
Difficulty: beginner

The Urban Heat Island effect (Cycle A)
Students investigate microclimate by taking measurements around their School's grounds.
Difficulty: beginner

Trees and air quality (Cycle A)
Students investigate the ways in which trees benefit air quality and determine how to landscape a home with trees to decrease energy use.
Difficulty: beginner

Weather and health (Cycle A)
A COMET learning module that describes weather and health. The section on everyday weather includes heat waves. There is also a game on weather and health. Registration is required (free registration) on UCAR's meted website.
Difficulty: beginner

3D Atlanta Heat Island (Cycle A)
Very interesting animations of of Atlanta's heat island and the development of convective clouds in the heat island.

Atlanta Heat Island: Landsat Land Use Classification and Thermal IR Data (Cycle A)
Compares land use and thermal IR imagery of Atlanta.

Beating the Heat in the World's Big Cities (Cycle A)
Provides an overview of the urban heat island phenomenon and describes prior heat waves.

Excessive heat events guide (Cycle A)
This EPA guide summarizes risks of excessive heat events. It also outlines procedures for notification and response.

Health Benefits of Urban Heat Island Mitigation (Cycle A)
This power point explores how urban heat islands exacerbate the effects of Excessive Heat Events (EHE) on morbidity and mortality.

Heat Island Effect (Cycle A)
Describes an urban heat island with links to mitigation and impacts.

NASA's Earth Observatory (Cycle A)
The Earth Observatory's mission is to share with the public the images, stories, and discoveries about climate and the environment that emerge from NASA research, including its satellite missions, in-the-field research, and climate models.

Zoom and Spin Around Atlanta: Daytime Thermal View of the Heat Island (Cycle A)
Contains daytime views of Atlanta's thermal islands.

Zoom and Spin Around Atlanta: Nighttime Thermal View of the Heat Island (Cycle A)
Uses thermal (infrared) imagery to show the Atlanta Heat Island at night.

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