FRESNO, Calif. – The federal agency tasked with calculating heat-related deaths may have been undercounting them for years – including in the San Joaquin Valley – according to a new national analysis.
Since 2018, the Centers for Disease Control and Prevention (CDC) has reported that an average of around 1,700 people die each year nationally of heat related causes.
But a recent investigation by NPR and Boston University projects that the national heat death average is much higher: 9,000 people between 2018 and 2025.
Researchers and journalists produced the new data using a statistical model built by both Boston University and NPR.
The investigation analyzed heat-related death numbers from the CDC and scaled them according to the U.S. population. The investigation found that the CDC significantly underreports heat deaths.
Quinn Adams, a research scientist at Boston University's Center for Climate and Health and the lead partner on the study, told NPR He believes that the annual average number of heat deaths could be higher as the research shows, but CDC data limitations are preventing a more accurate count.
Researchers broke down the data at a state and county level, including Merced, Fresno, Tulare and Kern counties. The results could have implications for at-risk populations, especially the elderly, children, those who have pre-existing illnesses, outdoor workers, lower income populations and people who do not have access to shade or air conditioners.
Valley health departments weigh in
Temperatures in the San Joaquin Valley are getting hotter, and heat waves are starting earlier in the year. The Valley endured record breaking heat in March, causing several cities to issue heat advisories and even impacting crops.
In extreme cases, high heat can also become deadly for vulnerable groups of people.
In two of the four Valley counties evaluated in the NPR and Boston University study, investigators estimate that far more people are dying of heat related causes than what the CDC is reporting.
The new analysis suggests Fresno County averages 27.6 heat deaths annually, while the CDC data estimates an average of only 4.2 a year.
In Kern County, investigators calculate an average of 23.3 heat deaths annually while the CDC reports only 7.4 a year.
The difference between the analyses was not so stark in Merced and Tulare counties.
There, the CDC recorded heat-related deaths as “NA” because fewer than 10 cases were reported each year. The NPR and Boston University analysis suggests Merced county averages 5.3 heat-related deaths a year while Tulare averages 11.1 deaths.
Michelle Corson, spokesperson for the Kern County Public Health Department, told KVPR in a written response that their department “does not routinely track heat-related deaths or other heat related outcomes.”
Fresno County Department of Public Health spokesperson Hope Megerdichian did not comment on the specifics of the new study, but did point to the Fresno County Heat Dashboard.
The only such dashboard in the region, it indicates trends in heat-related illnesses and is derived from data collected from Fresno County hospitals. It shows heat related emergency department visits peaked in 2024 and that paramedics responded to about 40 heat related calls in July of this year.
But the dashboard does not estimate heat-related deaths.
“We are eager to review the study once it is published. Once we have an opportunity to review, we may be able to provide additional insight,” Megerdichian wrote in a statement.
Dr. Kristen Sullivan, the public health director for Merced County, said tracking heat-related deaths has its challenges.
“Categorizing deaths is really kind of a halfway in between a science and an art,” she said.
Sullivan said heat is not usually identified as a contributing factor when someone with a pre-existing condition dies of something like a heart attack that may – or may not – have been caused by heat exposure.
“We base our death counts for the county on death certificate data,” Sullivan said. “It's so dependent upon the medical person who is filling out the death certificate.”
The effects of rising global temperatures
Nationwide, the study projects that Florida and Texas have the highest average number of heat deaths, with almost 2,000 deaths each year. This remained consistent when the data was adjusted for their large populations.
California ranked third with a projected average of 951.7 heat-related deaths a year.
Florida and Texas experience more humidity than California, which Sullivan, of Merced County, said can exacerbate heat related illness.
“When you sweat, if you're in a humid area, your sweat can't evaporate as much, and so the heat impacts your body more,” Sullivan said. “So because we're in such a dry area in the Valley, our sweat is able to do what it's supposed to do and help regulate our body temperature.”
Nighttime temperatures are also rising in many parts of the country.
According to Tracking California, a program of the non-profit Public Health Institute in partnership with the California Department of Public Health and the CDC, high temperatures at night leaves the body with fewer opportunities to cool off during heat waves – increasing the number and duration of extreme heat illnesses and deaths.
In August, Gov. Newsom announced the Extreme Heat Action Plan aimed at helping California communities adapt to evolving climate conditions.
All the Valley counties that were examined in the study have community cooling centers available during periods of extreme heat.
Here is a list of information regarding cooling centers in your county:
- Fresno County
- Kern County (Department of Aging oversees Cooling Centers in their region)
- Merced County
- Tulare County
- Mariposa County
- Madera County
- Kings County
