As a second heat wave is expected to hit the state in July, officials warn that the dangerous and dire consequences of extreme heat events will only worsen, in duration and severity, in a warming climate.
That grim outlook comes on top of new data showing just how intense the heat has been in California's interior.
According to data released this week by the U.S. Census Bureau, localities along the California-Arizona border had the longest streak of 90-degree days in the country in 2022.
According to the new data, residents in parts of eastern Riverside, San Bernardino and Imperial counties experienced streaks of 156 days, or more than 22 weeks, with temperatures of 90 degrees or higher in 2022. Some communities in nearby Yuma and La Paz counties in Arizona also experienced that many consecutive days with temperatures of 90 degrees or higher.
The federal government defines extreme heat in most of the country as two or three days with temperatures above 90 degrees. California, however, takes a more nuanced measure, basing extreme heat thresholds on a location’s average historical high temperature. In some cases, the state has classified extremely hot days as those that exceed 100 degrees.
Other areas in southeastern California, specifically Imperial, Inyo and eastern Riverside and San Bernardino counties, have seen more than 100 consecutive days of temperatures at or above 90 degrees in 2022, according to the new data.
Communities in Kern, Kings, Fresno and Tulare counties recorded the next longest stretches, with 91 or 92 days with temperatures at or above 90 degrees.
The Census released this data as part of its Community Heat Resilience Estimates, an effort to better understand vulnerabilities to extreme heat, a phenomenon that has become the deadliest weather event in the country.
“We know we need to be more prepared for this,” said Patricia Solis, executive director of Arizona State University’s Knowledge Exchange for Resilience program, which helped develop the heat-focused data set. “It’s hot and it’s getting hotter … We need to adapt our preparedness, response and resilience to the scale of the problem.”
At some point in 2022, more than three-quarters of California’s census tracts experienced a “heat event,” defined by the Census Bureau as two or more consecutive days where it reached 90 degrees or one day with a “wet bulb temperature” of 80 degrees or higher. The wet bulb measurement is the temperature reading from a thermometer covered with a cloth soaked in water, which slowly evaporates, mimicking the heat stress on the body when people sweat. Research has found that a wet bulb temperature above 85 degrees can begin to cause significant effects on daily life and human health.
More than 40% of communities that experienced a heat event had a high rate of households that are considered significantly socially vulnerable, with at least three risk factors that can exacerbate the impact of extreme heat or other disasters, according to federal officials.
The U.S. Census Bureau considered 11 social vulnerabilities, including households that potentially lack air conditioning, have financial difficulties or disabilities, lack health insurance or internet access, or have residents over the age of 65.
Solís said she hopes the data can help governments, community organizers, nonprofits and academics “target the people who need it most” when it comes to resources that help people become more resilient to extreme heat.
“This helps us to give it some visibility and helps us to better define where we focus our interventions,” he said.
