Temporal Trends in Absolute and Relative Extreme Temperature Events Across North America

Abstract

In this research, we define extreme temperature events using a recently defined excess heat factor, based on the exceedance of apparent temperature beyond the 95th percentile along with an acclimatization factor, to define extreme heat events (EHE). We extend the calculation to assess cold and develop relative metrics to complement the absolute metrics, where extremeness is based on conditions relative to season. We thus examine extreme cold events (ECE), relative extreme heat events, and relative extreme cold events in addition to EHE. We present a climatology of these variables for North America, followed by analyses of trends from 1980 to 2016. While EHE and ECE are found in the core of summer and winter, respectively, relative events tend to have a broader seasonality. Trends in relative extreme heat events and EHE are upward, and relative extreme cold events and ECE are downward; the relative events are changing more rapidly than the absolute events.Plain Language Summary One of the most critical ways in which weather conditions influence the environment is through extreme temperature events. While excessive heat and cold conditions have been amply studied, events that are extreme relative to the time of year have been less examined. These relative events may grab fewer headlines but can have important impacts on the environment, agriculture, and human health. In this research, we present a climatology of cold and heat events, both absolute and relative, for North America, followed by an analysis how they have changed from 1980 to 2016. Results show an increase in heat events and decrease in cold events across most of the United States and Canada. More interestingly, the relative events are changing slightly more rapidly than the absolute events. SHERIDAN AND LEE11,891 subsequent k-means cluster analysis. This process resulted in each grid point being categorized into one of 12 regions. Multiple numbers of regions (between k = 5 and k = 15) were examined, and ultimately 12 were chosen based upon qualitative assessment as well as 12 regions having the best variability skill score (Lee, 2014). These statistically derived regions were then used to inform a customized drawing of the final regions in ArcMap.

Changes in the frequency of hot, humid days and nights in the Mississippi River Basin

“…The slight difference in the geographical location of the downward trend may be explained by using different datasets and study periods. Defining the extreme heat events based on both absolute and relative thresholds over the period of 1980-2016 produced an upward trend in the frequency of heat events in southern MRB (Sheridan and Lee, 2018).…”

The gridded weather typing classification version 2: A global‐scale expansion

“…This spatial cohesiveness allows for easy visualization of the synoptic‐scale air masses influencing the weather in the mid‐ to high‐latitudes. For instance extreme events such as the March 2012 North American heat wave (Figure ; Sheridan and Lee, ), the 2003 European heatwave (Figure ; Valleron and Boumendil, ; Stott et al ., ), the December 1983 cold‐air outbreak over most of North America (Figure ; Smith and Sheridan, ), are readily identifiable when mapping daily weather types across the globe. Furthermore, predominant modes of variability in the tropics, such as El Niño events (Figure ), can be easily visualized as widespread and persistent air masses.…”

Spatial patterns of recent US summertime heat trends: Implications for heat sensitivity and health adaptations

“…Since heat-related mortality risks increase starting at relatively modest temperatures [4], the overall health burden on the 'warm tail' of a summertime temperature distribution is characterized both by high-frequency, low-impact days at moderate levels and by low-frequency, high-impact days at the upper extreme. However, previous assessments of health-relevant climatic trends tend to focus on the latter and quantify changes in terms of days exceeding an a priori threshold, such as record-breaking high ambient temperatures [5,6], or changes to the frequency of 'heat-wave days' [7][8][9] or other extreme climatic indices [10]. Since these analyses exclude a large portion of health-applicable heat, trends in the changes to the full distribution of moderate-to-extreme values are preferable for understanding how populations have experienced climate change and its health effects.…”