Sacramento ranks among worst cities for ‘heat island’ neighborhoods. New study shows why

Sacramento is ranked in the top 20 worst cities in the country for “heat island” neighborhoods that are significantly hotter than their surrounding environment, according to a report released Wednesday by Climate Central, a nonprofit news organization.

Climate Central’s report evaluated the effect of human development on increasing temperatures in cities. Among 158 cities ranked by the nonprofit, Sacramento came in 11th. New Orleans, Newark, New York City, Houston and San Francisco scored the highest for urban heat spikes.

“Neighborhoods in a highly developed city can experience mid-afternoon temperatures that are 15°F to 20°F hotter than nearby tree-lined communities or rural areas with fewer people and buildings,” the report found.

To score these cities, Climate Central used an index to evaluate the heat intensity in each city, which was based on research led by Valentino Sangrigorio of The Polytechnic University of Bari in Italy. These index scores reflected differences between average city temperatures and their surroundings.

The primary factors leading to a high-intensity score included the percentage of greenery in the city, population density, building height, heat reflection from buildings and roads, and the average width of streets.

Sacramento’s index score was 7.08 degrees, which is higher than Fresno’s at 6.97, but lower than New Orleans at 8.94.

While the study used average scores for each city, certain neighborhoods within each were cooler or hotter depending on a variety of factors, said Peter Girard, director of communications for Climate Central. The study noted that temperatures were hotter in Sacramento because of a high level of pavement compared to greenery or trees in some neighborhoods, among other factors.

Although Sacramento is known for its spectacular tree canopy, not all neighborhoods were built the same. The Sacramento Bee and other news organizations have reported that some low-income neighborhoods with higher populations of non-white residents can be 5 to 20 degrees hotter in summer compared to wealthier neighborhoods with a larger tree canopy.

It’s an inequity seen in dozens of cities across the U.S. In Baltimore, for example, the difference between the coolest and hottest neighborhoods could be as much as 10 degrees — and that’s one of the less extreme cases NPR reported in 2019.

Based on surface thermal data from NASA and U.S. Geological Survey satellite imagery, there was a correlation between heat and income in Sacramento at a level similar to Baltimore, NPR found.

In Sacramento, the urban forest is a kind of patchwork. Wealthier neighborhoods like Land Park, East Sacramento and the Pocket have a higher-than-average number of trees, compared to the rest of the city. But low- to moderate-income areas like Meadowview, Del Paso Heights, Parkway, Robla and Valley Hi are hotter compared to other parts of the city, as were industrial parks in North Sacramento and along Power Inn Road.

‘A chronic health problem can be exaggerated’

As illustrated in Climate Central’s new report, urban areas are warmer because pavements, buildings and other non-natural surfaces absorb and retain heat. In comparison, trees, green roofs and vegetation can lower temperatures in cities by providing shade for buildings, deflecting the sun’s radiation and releasing more moisture into the atmosphere.

Extreme heat can also exacerbate serious health problems, such as extra stress on people with chronic conditions like heart disease, worse air quality that aggravates respiratory conditions like asthma, heat exhaustion and even death.

“For the most part, anything that’s a chronic health problem can be exaggerated by high heat,” said Girard with Climate Central.

The effects of extreme heat are especially prominent for historically underserved populations and people living in urban communities, according to the report. Poverty is a major factor in determining not only who develops chronic conditions like heart disease and asthma, but also whether they’re able to get treatment.

Beyond safety concerns, hotter weather can also be costly for residents. Higher temperatures mean more energy used to keep homes cool, further burdening families who already see a large part of their income go to utility bills. One 2014 study found that low-income households typically spend 16.3% of their total annual income on utility bills, compared to 3.5% for other households.

“Things like the economic pressures on households to either afford or use air conditioning can make a difference in whether people take steps to keep themselves safe,” Girard said.

Sacramento already experiences extreme heat waves during the summer, and climate change will only intensify them. Scientists expect the region will get hotter and drier if greenhouse gas emissions aren’t reduced. A UC Davis report estimates temperatures in the Sacramento Valley could be 10 degrees higher in the summer by the end of the century.

Your health and the urban forest

Researchers have long identified tree canopies as being a simple but effective way of keeping streets cooler and making communities healthier. More trees improve air quality, contributing to lower rates of asthma and obesity, and can mitigate the extreme effects of climate change in a future where days will be hotter and drier.

With heat being the number 1 weather-related killer in the United States, the effects of heat exposure will likely only get worse as climate change makes extreme heat events worse and more frequent.

Girard has hope. Urban heat islands are one of the few areas of climate science with “readily available” solutions that can be quickly incorporated into cities, he said. By changing the way cities are built to include more green spaces and fewer paved areas, cities can decrease the negative effects created by urban heat islands, Girard said.

“Creating green space in natural space is probably one of the most effective and easily achievable ways for cities to change their urban heat Island intensity,” Girard said.

This story was originally published July 14, 2021 at 7:00 AM.