I have been sending out this resource all year, but I'll send it out again. From the US Department of Energy:
Creating a Cool Room for Extreme Heat Events
"Given the reality of global climate change and the increasing likelihood of extreme heat events, designing and retrofitting homes for resistance to extreme heat and power outages should be considered in all climates. Extending the "hours of safety" that a home can provide when air-conditioning is not available can be life-saving...."
https://basc.pnnl.gov/resource-guides/creating-cool-room-extreme-heat-events#edit-group-description