San Francisco Bay Area heat waves are getting longer and hotter

Data: EPA ; Note: Includes 50 most populated metros; New York City, Houston, Minneapolis-St. Paul and Denver were excluded for incomplete data in this period; Chart: Axios Visuals

This week's heat wave is looking more intense and longer-lasting than previously expected.

Why it matters: The trend is expected to continue, with heat waves lasting longer and occurring more frequently than they used to across the U.S. as cities scramble to boost climate resilience efforts .

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By the numbers: In San Francisco, the duration of heat waves — measured as a period of two or more consecutive days when the daily, humidity-adjusted temperatures topped the 85th percentile of historical summer temperatures — has increased by an average of three days since 1961, according to data from the EPA.

• The number of events per year has risen by nearly eight, while the average heat wave season — or the number of days between the first and last events — has stretched by almost 110 days since the 1960s.
• The average temperature above the local threshold that defines a heat wave has also increased by 0.2 degrees Fahrenheit.

Driving the trend: Human-caused climate change is increasing the likelihood, severity and duration of heat waves.

• Climate proofing buildings against extreme heat will be imperative.
• That could look like installing sensors to monitor thermal conditions, programming shading panels to respond to real-time insulation and fine-tuning air conditioning and ventilation.

Data: EPA ; Note: New York City, Houston, Minneapolis-St. Paul and Denver are excluded for incomplete data in this period; Chart: Axios Visuals

The big picture: The start of July is expected to usher in up to two weeks of triple-digit temperatures across much of California, Oregon and portions of Nevada.

• The heat itself will be " life-threatening ," according to the National Weather Service.
• Dozens of daily, monthly and even some all-time records may fall.

What they're saying: "I'm not so sure that really any of us will have seen this many days at this sustained level of heat, both daytime and most importantly nighttime heat," said UCLA climate scientist Daniel Swain in a video briefing this week.

• Many locations won't drop below 70°, or even 80°, for more than a week, making cooling access paramount.
• "It cannot be stressed enough that this is an exceptionally dangerous and lethal situation," the NWS office in San Francisco stated early Wednesday.

Between the lines: The heat will rapidly dry out vegetation, making it susceptible to wildfires.

• The Thompson Fire in Butte County, which broke out Tuesday and burned homes overnight, may be a preview of more destructive fires to come.

What we're watching: The city released a strategic plan to address the impacts of extreme heat and wildfire smoke last year, noting that residents can no longer rely on sub-80-degree weather and ocean breezes.

• San Francisco is particularly vulnerable because "our bodies, buildings, infrastructure, services, and communities are not designed for extreme temperatures and poor air quality," the report noted.
• Officials have since partnered with community groups to provide air conditioning for use during extreme heat.