June 2026
No Longer Hidden
This Heat Action Day, Tracking California releases new data showing who is hit hardest by extreme heat – and who’s been overlooked.
 
 
Unhoused Californians account for nearly 1 in 10 heat-related Emergency Department visits, despite representing less than 0.4% of California’s population.
For years, the people most affected by extreme heat were hidden in the data. Improved hospital coding now shows who was missing—and reveals a burden of heat-related illness that is far larger and more unequal than previously understood.
These findings have important implications for how we track, plan for, and respond to extreme heat, particularly in communities most at risk.
This month, we are publishing three data briefs that together, tell that story.
 
Invisible Patients:
Who’s Missing from the Data?
For years, what looked like missing data was actually a missing population. This brief shows that most of those left out were experiencing homelessness - and that leaving them out means we’re missing the people who may need the most care.
Read the brief →
 
 
Heat and Homelessness: Disproportionate Impacts
With this population now visible, a clear pattern emerges: Californians experiencing homelessness are getting sick from heat at much higher rates than everyone else.
Read the brief →
 
 
Extreme Heat Days Hit Unhoused Californians Hardest
We compared 2019-2022 emergency visits to understand how heat affects heart, lung, and heat-illness conditions in people with and without housing. We found that unhoused Californians, especially Black individuals and older adults, face significantly higher risks.
Read the brief →
 
 
Together, these briefs show who was missing from the data, how big the impact really is, and how extreme heat is making these gaps even worse.
Read all three briefs →
 
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