Unit 3: When Heat Is Trapped and Urban Heat Island Takes Over
Learning Objectives
By the end of this unit, you should be able to:
- Observe remote sensing imagery from different cities.
- Discuss and make connections about temperature and vegetation in different locations.
- Define the Urban Heat Island phenomenon.
Introduction
Welcome to Unit 3! In this unit, we will explore the Urban Heat Island phenomenon, which is a critical environmental issue where urban areas experience significantly higher temperatures than their rural surroundings due to human activity. By understanding it, we’ll uncover how urbanization, infrastructure, and land use influence temperature patterns.
Additionally, we will investigate the connections between temperature and vegetation in various locations. Vegetation plays a vital role in mitigating the impacts of heat and improving the quality of life in urban settings.
This unit will also introduce you to how remote sensing imagery helps scientists observe and analyze temperature and vegetation data across different locations. Through satellite data, we can study how climate and environmental changes impact urban and rural areas worldwide.
By the end of this unit, you’ll have a deeper understanding of how science and technology come together to address real-world climate challenges and how remote sensing serves as a key tool for environmental research.
Temperatures and Vegetation Map Activity
Now, we’ll take a closer look at remote sensing images that showcase data from different locations on Earth. This activity begins with images of New York City, followed by an activity with additional images from Atlanta and Baltimore, offering insights into how these urban areas vary in terms of temperature, vegetation, and climate.
These maps use visual data to represent key environmental factors:
- Temperature Maps: Show how heat is distributed across urban and rural areas, highlighting the Urban Heat Island (UHI) effect.
- Vegetation Maps: Illustrate vegetation cover, which can help mitigate temperature increases by providing shade and cooling through transpiration.
- Climate Data Maps: Offer a broader perspective on how weather patterns and long-term climate shifts affect urban areas.
As you analyze these images, focus on making detailed observations about what you see and drawing conclusions about the connections between vegetation and temperature. For example, observe how areas with dense greenery have cooler temperatures compared to highly urbanized regions. Consider what these patterns reveal about the relationship between human activity, vegetation, and temperature regulation.
Time to check for understanding!
�� Let's do a quick checkup summarizing this section, access the activity here
(https://app.nearpod.com/?pin=ZRCXQ)
☀️Urban Heat Island Phenomenon
What Are Urban Heat Islands? An Urban Heat Island is a phenomenon that is best described when a city experiences much warmer temperatures than in nearby rural areas. The sun’s heat and light reach the city and the country in the same way. The difference in temperature between urban and less developed rural areas has to do with how well the surfaces in each environment absorb and hold heat.
Shown to the right is a diagram displaying Earth's Energy Balance. To understand what is happening in the diagram, let's start with the radiation emitted by the Sun, represented by the yellow arrows. Radiation from the Sun can be absorbed or reflected. This is why some of the yellow arrows point right back to space, showing reflection. About 50% of the radiation from the sun that reaches the Earth is absorbed by the surface.
The surface absorbs the Sun's radiation and gains energy, warming the surface. The surface eventually releases some of this energy to the atmosphere above. Much of the energy is released as infrared radiation, which is detected as heat, like the warmth felt from a fire. This is shown by the red arrows. As the temperature of a surface warms, it will release more infrared radiation, regardless of what materials make up the object.
Another way that energy is released from the surface is through conduction and convection, shown by the curvy red arrow. Conduction transfers heat to cooler air that directly touches the hot surface. Convection occurs when air warmed by the surface rises upward, moving heat away from the surface. Convection from hot pavement is the reason that the air above a hot road on a summer day appears to shimmer. Both convection and conduction remove energy from the surface faster when the surface is much warmer than the air above.
A third way by which energy is transferred from Earth's surface is through evaporation, which is shown by the dashed red arrow. Evaporation is the changing of liquid water to an invisible gas called water vapor. This change requires energy, and evaporation is the reason that you cool off when you sweat. The surface of the Earth also "sweats". When water evaporates from Earth's surface, it transfers energy away from the surface, keeping it cool.
Earth's energy is often referred to as a "budget" or "balance". This is because the Earth is releasing the same amount of energy that it is gaining on average. The processes of conduction, convection, infrared radiation, and evaporation are all responsible for this balance. When something changes to throw off the balance, some of all of these processes respond. To talk about the movement of heat and energy, scientists use a theoretical object that is a perfect absorber (and hence perfect emitter) of heat and energy. They call this a blackbody because it absorbs all light and would appear completely black to us.
Time to check for understanding!
�� Let's do a quick checkup summarizing this section, access the activity here
(https://www.educaplay.com/learning-resources/21697474-unit_3_urban_he
at_island_phenomenon.html)
Where Do Urban Heat Islands Form?
The hottest places on Earth have a few traits in common. They are full of rock and stone, they do not have a lot of water, plants, or trees, and they are full of dark colors. Cities are full of these rocky surfaces — asphalt, brick, and concrete — that absorb heat by day and release it at night. These materials are used to make the sidewalks, parking lots, roads, and basketball courts of urban areas. Urban Heat Islands form because humans replace cooler natural surfaces with rocky surfaces.
These hard and dark-colored surfaces contribute to the Urban Heat Island effect in two ways. First, these surfaces have a low albedo, which increases the amount of energy from solar radiation they absorb. Second, these surfaces do not contain much water to evaporate, meaning that less of the absorbed energy evaporates water, and more goes into warming the surface and releasing energy by conduction, convection, or radiation. The combination of these factors means that cities and other highly developed areas are hotter than the plant-covered countryside.
Urban areas often see temperatures sometimes rise 6°C (10°F) hotter than the surrounding suburbs and rural areas. Cities tend to be hotter than their surrounding areas at all times of the day and at all times of the year. However, a variety of factors influence the Urban Heat Island. Bigger cities tend to have stronger heattrapping capacities than smaller cities. Cities surrounded by forest have more pronounced heat islands than do cities in arid environments, since replacing forests with paved surfaces in urban areas has much more of a warming effect than replacing dry sand and rock with pavement.
Time to check for understanding!
�� Let's do a quick checkup summarizing this section, access the activity here
(https://www.educaplay.com/learning-resources/21698188-unit_3_where_do_urban_heat_islands_form.html).
Why are Urban Heat Islands a Problem?
Urban Heat Islands are one of the easiest ways to see how human impact can change our planet. Sidewalks, parking lots and skyscrapers wouldn’t exist if humans weren’t there to build them. And although these structures are essential to city living, the heat islands they create can be dangerous for humans.
In the summer, New York City is about 7°F (4°C) hotter than its surrounding areas. That doesn’t seem like much, but these higher temperatures can cause people to become dehydrated or suffer from heat exhaustion. The hot temps also require more energy to operate fans and air conditioners. This can lead to power outages and a serious danger to public health.
Discussion
Now, you will take the information that you have learned in this unit and you will discuss your thoughts on the following question:
How can urban planning strategies, such as incorporating vegetation and green spaces, help mitigate the Urban Heat Island phenomenon, and what role does remote sensing imagery play in shaping these strategies? Share your thoughts on vegetation, green spaces and the Urban Heat Island.
�� Access the discussion task for this unit 1 here (https://app.nearpod.com/?pin=GKY7W
References
https://earthobservatory.nasa.gov/images/6800/new-york-city-temperature-and-vegetation
https://mynasadata.larc.nasa.gov/basic-page/urban-heat-islands
https://mynasadata.larc.nasa.gov/basic-page/earths-energy-budget