Climate Conditions Associated with Heat Related Emergency Dispatches

The reputation of Phoenix, Arizona, USA, is for being unbearably uncomfortable during its long, hot summer. Its historical mean monthly maximum temperatures reach over 33°C in May, rises to nearly 39°C in June and August, and tops out in July with a mean maximum temperature of 40°C. However, many days far exceed these mean maximum temperatures – often hitting temperatures into the mid to high 40s, and reaching 50°C on two occasions. The early summer season months have low humidity. However, from early July through early September is the monsoon season – which brings rising humidity along with the high temperatures. Phoenix's increasing temperatures associated with the urban heat island effect can exacerbate an already brutal climate. As would be expected, increasing summer heat brings increasing numbers of heat related health emergencies. This study examines the local climate conditions related to the heat related emergency dispatches from 2001 through 2006 for metropolitan Phoenix. Not surprisingly, the average number of emergency dispatches tracks similarly to monthly mean temperatures, and with maximum diurnal temperature. However, days with a large number of heat emergency calls are highly variable throughout the warm months spanning April to September – most days having no calls and some days with more than 30. The heat related dispatch data set does not lend itself to simple explanations such as the maximum temperature, heat index or day of the week. For example, there are many days in April and May with sudden increases in heat related emergency calls – days with low humidity, and relatively low temperatures – at least in comparison to the considerably hotter months of June and July. This study presents some of the patterns and complexities associated with the spikes in heat related emergency dispatches, primarily in relation to the local climate conditions, and also takes into consideration other possible contributing factors such as proximity to holidays.