LAS VEGAS — As spring temperatures began to climb in Phoenix, Dr. Jeffrey Johnston prepared for a grim summer trend featuring numerous fatalities.

In the past decade, Johnston, the chief medical examiner for Maricopa County, Arizona, has witnessed an alarming rise in deaths attributed to extreme heat. The heat-related fatalities in the county surged from several dozen in 2014 to 645 in 2023.

“The spike was so severe and prolonged that we approached it as a mass casualty incident,” he commented, referring to the recent summer.

However, Maricopa County—home to the most populated area in the desert southwest—has made significant investments in heat preparedness and mitigation strategies. Cooling centers in Phoenix are now operational every day of the week. The county has scaled up its heat safety communications efforts and appointed a full-time heat mitigation coordinator.

Consequently, there were fewer heat-related deaths last year compared to the previous year, despite experiencing record temperatures for the first time in a decade. With summer concluded, officials are reviewing the year’s achievements, and initial data indicates that the trend of decline is continuing: Maricopa County has reported 185 heat-related fatalities so far, significantly lower than the 284 reported at the same time last year.

In contrast, a troubling situation is arising in Clark County, Nevada’s second most populous area, which includes Las Vegas. The fatalities from heatstroke here have more than tripled within three years, reaching a record high of 513 in 2024. While the current year’s death toll is still not finalized, it is expected that the number of heat-related deaths will be in the hundreds.

Ariel Choinard, a scientist at the Desert Research Institute in Las Vegas, noted that last summer’s extreme heat served as a major wake-up call.

“Seeing a 120-degree temperature in Las Vegas made people realize, ‘Oh my gosh, this is really serious,'” she said.

Choinard has been pivotal in local initiatives addressing heat-related fatalities in Clark County and is tracking advancements in Maricopa County. She recognizes there is still work to be done.

“They began tackling the heat issue earlier than we did here, so they have made more progress in several respects,” she remarked.

Heat causes more fatalities in the United States each year than other weather-related disasters such as hurricanes, floods, and tornadoes, as reported by the National Weather Service. As climate change exacerbates the frequency and severity of heat waves, these two counties in one of the fastest-warming regions of the U.S. exemplify the urgent measures needed to preserve lives in light of this escalating threat and the severe consequences of inaction.

“All of these deaths are preventable.”

Heat disproportionately affects vulnerable populations. Individuals lacking access to air conditioning, including those experiencing homelessness or residing in low-income areas or mobile homes, face heightened risks. Outdoor workers, people with pre-existing conditions, and the elderly are also at increased danger.

In Maricopa County last year, 49% of heat-related deaths were linked to homelessness, while 57% were due to substance use. Therefore, strategies aimed at preventing fatalities from extreme heat must prioritize these vulnerable groups.

Maricopa County sought to address this by expanding its network of cooling centers and hydration stations in 2023, especially after experiencing 31 consecutive days of record-breaking temperatures of 110 degrees or higher that led to a rapid increase in heat-related deaths.