Fresno ranked among top ‘urban heat islands’ in the US. Why that’s bad for public health
Fresno has one of the most intense urban heat islands in the country, according to a new report by the nonprofit news organization Climate Central. Fresno stands with other California cities such as San Francisco, Sacramento, and Salinas on a list of the top 20 urban heat islands in the United States.
Generally, urban heat islands calculate the temperature difference between a city and its surrounding areas. However, temperatures can vary widely within a city depending on the prevalence of green space, parks, and other factors, creating smaller, intra-urban heat islands.
According to the report, the main contributors to Fresno’s urban heat island are “impermeable surfaces” of the city’s topography. Surfaces like asphalt and concrete, which don’t allow water to penetrate, are examples of impermeable surfaces that worsen urban heat islands. Stretches of hard, dark surfaces absorb heat and then radiate it back into the community.
More than just a question of comfort, heat is a public health risk that can be life-threatening ‒ and it impacts communities differently.
Air Conditioning in an urban heat island
Cranking the air conditioning is a tempting strategy for surviving the heat.
But more air conditioning isn’t the solution to the urban heat island. Air conditioners, the report said, “dump heat into the surrounding atmosphere.” A study by the Lawrence Berkeley National Laboratory suggested that air conditioning from urban buildings can add 20% more heat to the outside air compared to typical summer weather.
Furthermore, higher cooling needs put more demands on the electric grid, which raises electric bills. Lower-income communities, who tend to live in less energy-efficient homes, end up paying disproportionately higher energy bills.
To curtail rising energy costs and embrace a more sustainable form of energy, the city of Fresno established its first large solar energy farm in west Fresno earlier this year.
Fresno’s urban heat island and trees
Urban downtown spaces, areas with heavy industrial activity, and neighborhoods with fewer trees typically have the most intense urban heat island effects.
Low-income neighborhoods and communities of color are also disproportionately impacted. “Neighborhoods experiencing higher intensity urban heat islands were often the same ones subjected to discriminatory, race-based housing practices known as redlining,” the report says.
The heat island effect is also related to the presence of trees and green space in a community, as measured by American Forests’ Tree Equity Score. Many parts of the city are what Tree Fresno CEO Mona Cummings calls “under-treed.” According to American Forests, Fresno needs 1.9 million more trees to achieve “Tree Equity.”
Trees can provide multiple benefits to a neighborhood. Their presence improves air quality, provides shade, lowers temperatures, and even lowers energy bills. But tree canopy cover in Fresno is unevenly distributed. Neighborhoods that are whiter and more affluent tend to have more trees than lower-income neighborhoods.
Climate Central suggested that planting trees, especially along paved streets, can mitigate the heat island effects. “Shaded surfaces may be 20–45°F (11–25°C) cooler than the peak temperatures of unshaded surfaces.”
The report explained that in addition to providing shade, vegetation cools neighborhoods in other ways. The presence of vegetation leads to cooler temperatures through evaporation. “Because evaporation is a cooling process, the surrounding air slightly cools.”
Air quality worsens in an urban heat island
According to the National Weather Service, heat is the leading cause of death among weather-related fatalities.
The central San Joaquin Valley has experienced heat waves during this already hot summer. Urban heat islands can intensify the impact of these heat waves, which can create dangerous conditions for the populations that reside in them.
In addition to heat’s detrimental effects on health, urban heat islands intensify another health hazard: air pollution. According to Climate Central, heat traps pollutants in the lower atmosphere, which creates a phenomenon known as stagnation. Long-term exposure to this pollution can cause asthma, worsen allergies, and cause other respiratory health problems.
The central San Joaquin Valley has some of the worst air quality in the nation, and health advocates say the prevalence of conditions like asthma in communities of color are an example of systemic environmental racism.
Local youth environmental advocates have urged the city to see the relationship between environmental factors like urban heat islands and air quality and the presence of gang and gun violence through the lens of a public health concern rather than one of criminal justice.
Melissa Montalvo is a reporter with The Fresno Bee and a Report for America corps member. This article is part of The California Divide, a collaboration among newsrooms examining income inequity and economic survival in California.
This story was originally published July 21, 2021 at 5:00 AM.
