A
heat wave or
heatwave, sometimes described as
extreme heat, is a period of abnormally hot weather. A time period of
five consecutive days is often used to define a heat wave but the exact definition of a heat waves can vary for different countries. A
heat wave is usually measured relative to the usual climate in the area and to normal temperatures for the season. Temperatures that humans from a hotter climate consider normal, can be regarded as a heat wave in a cooler area. This would be the case if the warm temperatures are outside the normal climate pattern for that area. High humidity often occurs during heat waves as well. This is especially the case in oceanic climate countries. Heat waves have become more frequent, and more intense over land, across almost every area on Earth since the 1950s, the increase in frequency and duration being caused by climate change.