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Thermal Islands: Cycle C

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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
Classroom Application Cycle

This cycle you will develop cooperative activities that engage your students in understanding Earth as a system through analyzing the causes and effects of the event in this module. You also have the option of choosing a Local Event as the focus of your application. Use the resources listed below to develop your ideas. Submit your ideas for your teammates to rate and for your instructor to grade.



  • Review the Individual Classroom Application and Rubric.
  • Create or adapt activities to help your students develop the concepts you have explored in this module. You may choose to do a Local Event Analysis for extra credit this cycle and then base your Classroom Application on it. If you choose to do a local event analysis and then also develop it for your classroom application, you can satisfy this cycle's requirements and receive extra credit.
  • After submitting your own classroom application to the course discussion space, recruit a classmate to rate and make comments on your classroom application. Refer to the Classroom Application Goal and Rubric.

Upload to ESSEA your classroom application with a description of its relevance to students, connection to the curriculum, instructional strategy and assessment methods. Include a reflection on what and how you have learned about Earth System Science and this event as a result of this module. Complete the rubric.
Deadline: Tuesday, March 21 2017 11:59 PM (Eastern Time)
Upload Assignments

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Mapping Local Data in GIS (Cycle C)
From the Earth Exploration Toolbook. Explores the relation between land cover and surface air temperature.
Difficulty: advanced

Weather and the Built Environment (Cycle C)
A COMET learning module that describes weather and built environment. Includes a section on the urban heat island. Registration is required (free registration) on the Univerity Corporation for Atmospheric Research's (UCAR) meted website.
Difficulty: advanced

Digital Library for Earth System Science (Cycle C)
The ultimate resource for Earth Science lesson plans, investigations and publications.

MetEd (Cycle C)
Meterology, weather forecasting and related geoscience topics training and teaching resources. Registration is required to access modules and courses.

Lesson plans, activities, resources and more using NASA data.

NASA's Climate Kids (Cycle C)
News, information, games, teacher resources and more.

NASA's Global Climate Change (Cycle C)
Climate key indicators, evidence, effects, interactives, images and more. Educator tips and tricks for use in your classroom are provided.

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