Shade vs Sun: Summer sidewalk temperatures in Tucson, Arizona

Sunlight heats up pavement, causing sidewalks and roads to become significantly hotter than the surrounding air. And if there are no trees, plants, or sheltered areas, there’s no temperature-lowering shade.

When sidewalks and traffic islands are planted with cooling native flora and trees, communities can be greener, a bit quieter, friendlier for local birds and insects, and shadier for everyone. In this summer video, Brad Lancaster measures temperatures on public walkways that have shade and full sun during a 101°F (38°C) day in Tucson, Arizona.

The permaculture pro, regenerative design advocate, and author also promotes his book, which advocates for greener spaces, shade harvesting, and “planting” the rain for positive effects across landscapes and communities.

Vegetation not only provides shade, it creates a cooling effect through evapotranspiration, a combination of evaporation—”the movement of water directly to the air from sources such as the soil and water bodies”—and transpiration—”the movement of water from root systems, through a plant, and exit into the air as water vapor.” Via Resources for the Future:

“Heat islands form as a result of altered landscapes in cities. Some of the main contributing factors are:

• Urban surfaces. Human-made building materials such as pavement and concrete reflect less sunlight and absorb more heat than natural surfaces. These urban surfaces quickly heat up during the day and slowly release heat at night, contributing to higher temperatures around the clock in cities. In contrast, natural landscapes such as trees, vegetation, and water bodies cool the air by providing shade, transpiring water from plant leaves, and evaporating surface water.

• Urban geometries. Tall buildings can create an urban canyon effect that blocks wind flow and traps heat near the surface where humans can feel it.

• Anthropogenic heat. In cities, people drive cars, run air conditioning units, and operate buildings and industrial facilities in close contact with each other—activities that generate waste heat that increases local temperatures. When these heat-generating activities are concentrated over small areas, they can have significant impacts on the microclimate.

• Urban greenhouse effect. Urban atmospheres usually contain higher concentrations of pollutants and have higher water vapor content. Combined with warmer air, these factors can trap and amplify heat above cities.”

The sunny wall is hot, but the sidewalk is even hotter. Are there areas on playgrounds or sidewalks where you live that could be improved with cooling native plants and trees? Related reading at KQED: How Greening California Schoolyards Protects Kids and the Climate.

Brad Lancaster is on YouTube and Instagram, and at HarvestingRainwater.com.

Plus, watch these related videos on TKSST:
• What happens if you cut down all of a city’s trees?
• Do Cities Need More Green Roofs?
• How can design make climate-resilient buildings?
• Warka Water towers harvest drinkable water from the air
• How to make a Moser Lamp: 60 watts of free, natural light
• A sustainable cooling system made with wet terra cotta cones