The California Heat Assessment Tool (CHAT) was developed to help state and local public health officials understand how heat vulnerability will change with increasing temperatures due to climate change. The tool helps users identify heat vulnerable areas based upon changes in high heat days under different climate scenarios and social, health and environmental vulnerability factors. The study defines “Heat Health Events” (HHEs) as heat events that cause negative public health impacts – and the study found that vulnerable groups may be more sensitive to high-heat days by as much as 6 to 8 degrees Fahrenheit as compared to the general population. The tool helps users determine how climate change will affect the severity, duration, and shifts in timing of HHEs under different emissions scenarios.