Heat Waves

What are they?

Heat waves are periods of abnormally hot weather that typically last two or more days. While there is no single definition for a heat wave, they are generally determined when the temperatures exceed some threshold for a sustained amount of time. They usually have the most impacts during summer months when normal temperatures are already high. In the Southeast US, where North Carolina is located, heat waves often occur when an area of high pressure (also called a “ridge”) sits over the region for an extended period of time. When there’s a high pressure system in place, we typically experience clearer skies and fair weather. As the sun shines down, it warms the surface and, because high pressure in the atmosphere acts like a dome or a cap, that heat is trapped in place. When this weather pattern is in place for a few days in a row, our temperatures can creep up, stay high, and lead to an extreme heat event.

Consistent with historical trends the state is projected to warming temperatures, especially nighttime temperatures. The likelihood of extreme heat events is also projected to increase in the state, making extreme heat an important hazard to be prepared for.1 Rising average temperatures and more frequent and more intense heat waves due to climate change are affecting human health in several ways. Most directly, warmer average temperatures and more extreme temperatures put more people at risk for heat-related death and disease, such as heat stroke and dehydration.3 

Figure A. Memorial Day weekend 2019 (Image from NOAA)

Why should I care?

There are a number of negative impacts from heat waves, including:

1Kunkel, K.E., D.R. Easterling, A. Ballinger, S. Bililign, S.M. Champion, D.R. Corbett, K.D. Dello, J. Dissen, G.M. Lackmann, R.A. Luettich, Jr., L.B. Perry, W.A. Robinson, L.E. Stevens, B.C. Stewart, and A.J. Terando, 2020: North Carolina Climate Science Report. North Carolina Institute for Climate Studies, 233 pp. https://ncics.org/nccsr

2Luginbuhl, RC; Jackson LL; Castillo DN; Loringer KA. heat-related deaths among crop workers — United States, 1992—2006. MMWR 2008;57(24);649-653. <http://www.cdc.gov/mmwr/PDF/wk/mm5724.pdf> Accessed February 17, 2021.

3Portier CJ, et al. 2010. A human health perspective on climate change: a report outlining the research needs on the human health effects of climate change. Research Triangle Park, NC: Environmental Health Perspectives/National Institute of Environmental Health Sciences. doi:10.1289/ehp.1002272 <www.niehs.nih.gov/climatereport> Accessed February 17, 2021.

4North Carolina Division of Public Health, Occupational and Environmental Epidemiology. The 2020 North Carolina heat report. <http://publichealth.nc.gov/chronicdiseaseandinjury/doc/HeatReport20-2012.pdf> Accessed February 17, 2021.