Frequency and Intensity Of Heat Waves In East Tennessee: Measurements Using Various Heat Wave Definitions

Introduction: More frequent and intensive heat waves have been generally considered as a consequence of global climate change. In spite of the fact that there is a lack of generally accepted definition of heat waves in terms of intensity and duration, the adverse impacts of heat wave are undeniable. East Tennessee has experienced noticeably higher summer temperatures in the recent past, including possible deadly heat waves. This study aims at measuring the frequency and duration of heat waves in East Tennessee over the last ten years using various heat definitions extracted from epidemiological literature. Methods: A literature search was conducted in PubMed using key words: Heat wave, mortality and morbidity. The search located 311 peer-reviewed articles that were screened and 108 were reviewed for heat wave definitions. The definitions used in the 108 articles were then summarized and seven most commonly used definitions were selected for this study. Daily temperature (mean, maximum and minimum) data from three weather stations namely Tri-City Airport, Kingsport and Elizabethton in East Tennessee were collected for the period from 2008 to 2017 to test the seven different definitions of heat waves. The World Meteorological Organization (WMO)’s definition “daily maximum temperature for more than five consecutive days exceeding the average maximum temperature (for the 30-year normals period) by at least 9º Fahrenheit (5º Celsius)” was also tested and compared with the seven definitions extracted from epidemiological literature. Results: Using the WMO definition and temperature data from the Tri-City Airport Weather Station located in Bristol, TN, it was estimated that the total number of heat wave in the 10-year period was 58, which spanned a total of 1343 days, or 134.3 days per year on average. The results further indicate that the onset of heat wave days has been earlier within the past four years than the previous years with the earliest occurrence on February 24, 2017. Year 2016 is regarded as the hottest year in the period as virtually the whole of 2016 summer was a heat wave period. It is also worthy of note that the end-date of the heat wave episodes using the WMO definition is observed to have extended for the first time to the month of November as seen in 2016, which was not so for the other years. The heat wave episodes observed with the 97th percentile mean and 90th percentile minimum temperatures in Tri-City Airport Weather Station were lower than the WMO definition. Similar results were observed in Kingsport weather station. But in Elizabethton weather station, the 97th percentile mean and 90th percentile minimum temperatures produced higher episodes of heat waves but shorter days than the WMO definition. Conclusion: Heat wave is deadly and evidences suggest that its manifestation may become severe as more damages are being done to the atmosphere through pollution and deforestation. A reversal of this trend through early warning systems and preparedness is very important and urgent. Further research will look into the mortality health outcome associated with heat waves in this region.