Decadal changes in the frequency of United States heat waves

Heat waves are often cited as the major cause of weather-related deaths in the United States. With concern for global warming, it can be postulated that they are likely to increase in frequency. However, no comprehensive climatological analysis of their average frequency, duration, distribution, or intensity, nor of temporal changes, has been undertaken. This is partly because there has not been an adequate definition of a heat wave. A definition is proposed here, based on a combination of the National Weather Service heat stress warning criteria and exceedence thresholds derived from historical temperature and humidity information. Using the definition, changes in heat wave characteristics between decades are assessed, and estimates of the overall long-term trends developed.