Environmental Science: Urban Heat Islands and City Planning Worksheet

Question 1

Define the term urban heat island. In your answer, identify two human-made features that often make cities warmer than nearby rural areas.

Accepted Answer

An urban heat island is an area in a city that is warmer than surrounding rural areas because of human-made surfaces and activities. Asphalt roads, dark roofs, concrete buildings, limited vegetation, and waste heat from vehicles or air conditioners can all increase city temperatures.

Question 2

A downtown neighborhood has an afternoon air temperature of 36.5°C. A nearby rural area has an afternoon air temperature of 31.8°C. Calculate the urban heat island intensity.

Accepted Answer

The urban heat island intensity is 4.7°C because 36.5°C minus 31.8°C equals 4.7°C.

Question 3

The table shows surface temperatures measured at 3:00 p.m. on a summer day: black asphalt road, 58°C; concrete sidewalk, 44°C; grass field, 32°C; tree-shaded grass, 28°C. Which surface is likely contributing the most to heat buildup, and why?

Accepted Answer

The black asphalt road is likely contributing the most to heat buildup because it has the highest measured surface temperature at 58°C. Dark asphalt has low reflectivity, so it absorbs a large amount of solar energy and releases heat to the surrounding air.

Question 4

Explain how albedo affects urban temperatures. Include an example of a city planning choice that would increase albedo.

Accepted Answer

Albedo is the fraction of sunlight a surface reflects. Surfaces with higher albedo reflect more solar energy and absorb less heat, which can lower surface and air temperatures. A city can increase albedo by using cool roofs, light-colored pavement, or reflective road coatings.

Question 5

A city replaces a 10,000 square meter dark roof with a cool roof. The dark roof absorbs 85 percent of incoming sunlight, while the cool roof absorbs 45 percent. If 800 watts per square meter of sunlight reaches the roof, how much less solar power is absorbed after the change?

Accepted Answer

The cool roof absorbs 3,200,000 watts less solar power. The dark roof absorbs 0.85 times 800 times 10,000, which is 6,800,000 watts. The cool roof absorbs 0.45 times 800 times 10,000, which is 3,600,000 watts. The difference is 3,200,000 watts.

Question 6

Describe two ways that trees can reduce urban heat. Your answer should include both shade and evapotranspiration.

Accepted Answer

Trees reduce urban heat by providing shade, which keeps pavement, buildings, and people from receiving as much direct sunlight. Trees also cool the air through evapotranspiration, a process in which water evaporates from leaves and carries heat away from the surrounding environment.

Question 7

A city map shows three neighborhoods. Neighborhood A has 8 percent tree canopy, many parking lots, and a median income below the city average. Neighborhood B has 35 percent tree canopy, parks, and a median income above the city average. Neighborhood C has 20 percent tree canopy and mixed land use. Which neighborhood should be prioritized first for heat reduction investments, and what environmental justice concern does this example show?

Accepted Answer

Neighborhood A should be prioritized first because it has the lowest tree canopy, many heat-absorbing parking lots, and lower median income. This example shows an environmental justice concern because heat risk and lack of cooling resources may be unequally distributed, placing a greater burden on residents with fewer resources.

Question 8

Explain why urban heat islands can increase electricity demand during summer afternoons. Include one possible feedback effect that can make heat worse.

Accepted Answer

Urban heat islands increase electricity demand because people use more air conditioning when outdoor temperatures are high. A feedback effect can occur when air conditioners release waste heat outdoors, which can warm streets and building surroundings even more, increasing the need for additional cooling.

Question 9

A planner proposes adding a large park, planting street trees, using cool roofs, and narrowing some roads to make room for bike lanes and green space. Choose two of these strategies and explain how each could reduce heat or heat exposure.

Accepted Answer

Adding a large park could reduce heat by replacing heat-absorbing pavement with vegetation that provides shade and evapotranspiration. Using cool roofs could reduce heat by reflecting more sunlight and absorbing less solar energy than dark roofs. Other valid strategies include street trees for shade and narrower roads that reduce asphalt area.

Question 10

A city has a heat emergency plan that opens cooling centers from 12:00 p.m. to 6:00 p.m. only. Explain one strength of this plan and one limitation that city leaders should address.

Accepted Answer

One strength is that cooling centers provide safe indoor spaces during the hottest part of the day. One limitation is that heat can remain dangerous into the evening and night, especially in dense urban areas where surfaces slowly release stored heat. City leaders should consider longer hours, transportation access, communication in multiple languages, and support for people without air conditioning.

Question 11

The graph shows that nighttime temperatures in a dense urban neighborhood stay above 29°C for five nights in a row, while a nearby rural area drops to 22°C each night. Explain why nighttime heat is especially dangerous for human health.

Accepted Answer

Nighttime heat is especially dangerous because the body needs cooler temperatures to recover from daytime heat stress. When temperatures remain high overnight, people have less chance to cool down, which increases the risk of heat exhaustion, heat stroke, dehydration, and stress on the heart and lungs.

Question 12

Design a short urban heat island study for your school or neighborhood. Identify the question you would investigate, the data you would collect, when and where you would collect it, and how the results could guide city planning.

Accepted Answer

A strong study might ask which surfaces or locations are hottest around the school or neighborhood. The data could include air temperature, surface temperature, shade cover, land cover type, and time of day at locations such as parking lots, sports fields, tree-shaded sidewalks, and building entrances. Results could guide planning by identifying where trees, shade structures, cool pavement, or cool roofs would have the greatest benefit.

Environmental Science: Urban Heat Islands and City Planning

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