Changes in heat waves and cold spells (1948–2012) based upon different thresholds of apparent temperature

With a continued focus on climate change, the impact of heat waves and cold spells remains an emphasis from an environment and health perspective. With increased global temperatures, some research suggests a shift in more extreme heat events at the expense of cold spells. Anomalous temperature events have long been associated with increased morbidity and mortality. More acute, elevated temperatures often lead to compromised cardio-respiratory systems, and, while more lagged, the influence of cold has also been linked to similar physiological responses. This research evaluates the changes in heat waves and cold spells for 60 cities in the contiguous United States (1948-2012). Daily mean apparent temperature was used to define the events using 3-day rolling averages. The 2.5th, 5th, 95th, and 97.5th percentiles allowed for two levels of events to exist. Events were based upon annual (year-to-year) and period (1948-2012) thresholds. Changes in duration, timing, and frequency, all of which have been shown to be important characteristics in regards to heat and cold events, were evaluated. Significant changes in some of these characteristics were found although spatial and temporal variability existed. Understanding the variability associated with and the observed, long term trends in anomalous temperature events is an important aspect to better preparing for these events.