Projected Increase in the Spatial Extent of U.S. Summer Heat Waves and Implications for the Energy Sector

A widely expected consequence of a warming climate is for summer heat waves to become more intense, more frequent and longer-lived. However, an important physical attribute of heat waves that has received comparatively little attention from researchers is their spatial extent, particularly the spatial extent of contiguous regions experiencing heat wave conditions. This paper examines the spatial extent of U.S. summer heat waves in the North American Regional Reanalysis (NARR) and in simulations and projections (RCP4.5 & RCP8.5 scenarios) of 11 CMIP5 coupled climate models. An algorithm is first applied to the respective gridded temperature datasets to identify contiguous heat wave regions, with several physical attributes then examined, including spatial extent, number of events, duration and cooling degree days. The exposed population (relative to a 2015 baseline) is also computed. For the current climate, the CMIP5 simulations are found to do a very good job in re-producing the heat wave attributes identified in NARR. Climate model projections show a near-doubling of all heat wave attributes by mid-century, including their spatial extent, cooling degree days and exposed population. Some implications for the energy sector will be discussed.