heatwaves

Heatwaves are extended periods of unusually hot weather, typically lasting several days. Definitions vary by region and agency, but most rely on temperatures that exceed a region’s normal range for an extended time, often two or more consecutive days or three or more days, and may involve high nighttime temperatures. Because normals differ by latitude and season, a heatwave in one location may be relatively common in another.

They arise when a persistent high-pressure system traps warm air aloft and suppresses cloud formation, creating a heat dome over an area. Atmospheric ridges, land-atmosphere feedbacks, and urban heat island effects contribute. Climate change is associated with increased frequency, duration, and intensity of heatwaves due to higher baseline temperatures and shifts in circulation patterns.

Health risks include heat exhaustion, heat stroke, dehydration, and worsened cardiovascular and respiratory conditions. Mortality tends to rise, especially among the elderly, children, people with preexisting conditions, outdoor workers, and residents without cooling access. Heat can stress power grids, reduce crop yields, and increase wildfire risk.

Public health systems issue advisories and cooling centers; cities implement urban heat mitigation such as trees, green spaces, and reflective surfaces; building codes improve insulation and cooling efficiency; and heat-health warning systems target vulnerable groups. Ongoing monitoring helps quantify impacts and inform policy.