We are now paying dearly for this extra heat. One sixth of the electricity consumed in the United States goes to cool buildings, at an annual power cost of 40 billion dollars. Moreover, a 5 degrees Fahrenheit heat island greatly raises the rate at which pollutants — nitrogen oxides and volatile organic compounds emanating from cars and smokestacks — ‘cook’ into ozone %hellip; The Los Angeles heat island raises ozone levels 10–15 per cent and contributes to millions of dollars in medical expenses.
AH Rosenfeld, JJ Romm, H Akbari & AC Lloyd, Painting the town white — and green[PDF], MIT Technology Review, February/March 1997
The Urban Heat Island (UHI) effect occurs when an urban area is warmer than surrounding areas. This typically happens in city suburbs and towns as the land surface is modified with materials that retain heat, such as dark roads and roofs. Lack of trees and greenbelts contribute to the problem, as does waste heat created by energy use. Mitigation strategies include planting more trees to create canopies, greening roofs, and using pale surfaces on roads and paths. In this chapter we look at studies from around the world.
Black roads and roofs in addition to a lack of trees cause soaring summer temperatures in Chippendale. By creating pale roads and roofs, and growing tree canopies over half the roads we could reduce the summer heat in the suburb by 6–8 degrees Celsius!
This map shows the temperatures of the suburb’s roads between 1:00 a.m. and 6:00 a.m. on 6 February 2009. The roads — which constitute over 23 percent of the suburb’s land area — were over 34 degrees Celsius. The houses, private land and parks were around 29 degrees Celsius. The roads act like night-time radiators by surrounding the suburb with hot air and making the buildings hotter at night. As a result the roads are still hot when the sun rises and the next day is hotter than need be, both inside houses and on the streets.
The heat dries out the trees and soil, which stunts tree and vegetation growth. To stay cool residents and businesses turn on air conditioners. Thus, the suburb’s roads are driving up electricity costs for everyone and increasing the pollution from the coal-fired power stations that provide the electricity. Think of all the electricity we’d save, and how much less pollution in the atmosphere, simply by creating pale reflective roads and increasing tree canopy cover.
The hottest roads on the map run east–west. They have the largest amount of black road surface exposed to the sun and are the least protected by buildings and trees.
The north-south roads are partly protected from the western summer sun by the buildings and have larger tree canopies (some of the trees grow larger than others in the east-west streets).
The effect of the roads, no matter the direction they face, is to increase the temperature of the whole suburb. This burdens the suburb, and all that lives within it, with an invisible island of hot, damaging air.
No law, design guidelines or goals have been put in place to make these hot roads cool. Until now. This plan offers affordable, easily constructed and maintained solutions to the Heat Island Effect in Chippendale.
And we can learn from suburbs and cities which have implemented changes to great effect. Let’s look at some success stories.
Plants Cool Suburbs
The suburb of Village Homes in the city of Davis, California is 6 degrees Fahrenheit cooler than the adjoining suburbs in summer. This is because the village contains 23 acres of greenbelts, orchards, vineyards, vegetable gardens and edible landscapes. The resulting tree canopies regulate temperature. Since 1978 the village has grown over 24% of its food in the streets and gardens. For more information see their Village Home Owners Association website.
One study analysed the costs and benefits of increasing numbers of street trees. By doubling the number of street trees they believe the city’s temperature can be reduced by 1.2 degrees Fahrenheit (.7 degrees Celsius). Planting the street trees would cost an estimated 625 million dollars and, with annual savings of 98.4 million dollars, it would pay off in just over six years. (See Kerr and Yao, quoted in Rosenthal, Crauderueff and Carter, 2008 [PDF])
In 1998 the South Korean city of Seoul removed a 12-lane freeway in the city centre and opened up a built over river. The reinstatement of the river led to an average reduction in summer temperatures of 3 degrees Celsius. Property values rose dramatically, and the river and its banks became a magnet for pedestrians, tourists, businesses and biodiversity. Traffic was reduced as well as travel times. The city integrated a broad range of travel solutions. For example: varying opening and closing hours of businesses and improving public transport options.
Healthier Suburbs & More Jobs: Greening the Ghetto
The Sustainable South Bronx project in New York is working to reduce the Urban Heat Island effect partly by greening the roads and creating parks. Their research confirms the damage done to human health by the combination of heat, road traffic, and lack of vegetation to clean and cool the air. Analysis of the impact of air pollution from vehicles suggests that potent environmental pollutants “at levels recently encountered in New York City air may adversely affect children’s cognitive development … with implications for school performance”(FP Perera, et al. Effect of Prenatal Exposure to Airborne Polycyclic Aromatic Hydrocarbons on Neurodevelopment in the First 3 Years of Life among Inner-City Children [PDF], Environmental Health Perspectives, 2006). With 1 in 4 children suffering asthma, greening one of the most polluted parts of New York was seen as a necessity.
South Bronx had the highest unemployment rate in the city, at 24 per cent, so Sustainable South Bronx set about training people and creating green jobs. “Greening our neighbourhood increases the focus on green jobs and brings more parks and green industry to the South Bronx,” says Miquela Craytor, Executive Director, Sustainable South Bronx See their video playlist.
More than half of the sunlight reaching the earth is invisible to the human eye, and this invisible sunlight heats the roof. A colored surface that reflects much of the invisible sunlight is a called a cool dark color, or cool color. A cool dark color reflects more sunlight than a similar-looking conventional dark color, but less than a light-colored surface. For example, a conventional dark colored surface might reflect 20% per cent of incoming sunlight, a cool dark colored surface, 40 per cent; and a light-colored surface, 80 per cent.
A study in urban heat mitigation using green roofing shows that savings can be substantial. One study estimated that cool roofs could reduce New York City’s heat island by 1 degree Fahrenheit (.6 degrees Celsius). They estimated savings of 105 million dollars per year — 23 million dollars in direct energy savings and 82 million dollars in indirect savings — if cool roofs were constructed on every roof in New York City (calculated at an average additional cost of 68 cents per square foot, compared to traditional roofing techniques). Under certain assumptions the cool roof payback period was about six years. See Kerr and Yao, quoted in Rosenthal, Crauderueff and Carter, 2008 [PDF].
Benefits of Mitigation
If we plant trees and change the colour of our roads and roofs from black to pale colours we will create multiple benefits. We will cut electricity bills and save money, increase bird and insect life, increase plant growth and significantly reduce our environmental footprint from less pollution.
Mitigation of the Urban Heat Island effect is a major part of the Chippendale Plan, and will be demonstrated throughout. But it is only one side of one story. Next, we’ll look at the comprehensive plan for our streets.