Abstract
The characteristics of urban heat vary across cities. High humidity levels pose a threat to public health for those in close proximity to coastlines, particularly for cities with higher average temperature. With temperatures rising around the world due human activity, developing a more complete understanding of the main determinants of extreme heat is important for predicting future heat levels. While average temperature for a city makes a good general descriptor for its climate, it alone can't give a complete picture, especially as it relates to human health. The variability around this average can better describe the climate and even serves as an indicator for the frequency of heat advisories needed. Using histograms of daily average and maximum readings for heat index and dry bulb temperature, different characteristics of each city's histograms were analyzed and compared against each other. We found that the upper range of a city's histogram is primarily dependent on latitude (R 2 of .713 for temperature, .408 for heat index), but is also influenced by average relative humidity, elevation, and distance from coast. This suggests that a city's most extreme heat values are closely tied to geographical constraints. By comparing our analysis with results from various heat-health studies, we also explored a potential definition of chronic heat as cities experiencing daily extreme heat values that lasted for more than 2 consecutive weeks and a total of 90 days out of the year.