A North American Heat Index Climatology

The changing climate has increased the importance for new studies concerning heat waves and the extreme mortality they cause. Using air temperature as the only indicator of heat does not accurately predict the apparent heat in a region. The heat index (HI) formula utilized by the National Weather Service provides a measure of the apparent temperature in the area, combining surface temperature and moisture. This study examines a North American heat index climatology and decadal trends over a recent 30-year (1980–2009) period and discusses the factors that contribute to the changes identified in the heat index values. One hundred and fifty six stations from NCEI hourly surface station data were used in this climatology (from U.S. and Canada) to provide a comprehensive outlook of the changes in heat index spatially as well as quantitatively. Statistical software and GIS were used to quantify, organize, and visualize the station data for multiple North American regions. Preliminary results show an increase in heat index values across much of North America over the 30-year climatology.  However, these increases are not uniform across the continent, with some locations seeing a greater contribution from increases in atmospheric temperature, with others seeing a greater contribution from increases in atmospheric moisture content.