Science Source

Heat waves in the United States: definitions, patterns and trends

States that high temperatures and heat waves are related but not synonymous concepts
States that heat waves, generally understood to be acute periods of extreme warmth, are relevant to a wide range of stakeholders because of the impacts that these events have on human health and activities and on natural environments
States there is no single, standard definition of a heat wave
Experts differ in which threshold values (absolute versus relative), duration and ancillary variables to incorporate into heat wave definitions
Uses data from the North American Land Data Assimilation System to examine patterns and trends in 15 previously published heat wave indices for the period 1979–2011 across the Continental United States
Finds that over this period the Southeast region saw the highest number of heat wave days for the majority of indices considered
Finds that positive trends (increases in number of heat wave days per year) were greatest in the Southeast and Great Plains regions, where more than 12 % of the land area experienced significant increases in the number of heat wave days per year for the majority of heat wave indices
Concludes noting that significant negative trends were relatively rare, but were found in portions of the Southwest, Northwest, and Great Plains