Heat wave
A heat wave[1] (or heatwave[2]), sometimes described as extreme heat, is a period of abnormally hot weather.[3]: 2911 Definitions vary but are similar.[4] A heat wave is usually measured relative to the usual climate in the area and to normal temperatures for the season.[3]: 2911 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.[5] 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. Heat waves occur from climate change.[6][7]
Not to be confused with heat burst.
Heat waves form when a high-pressure area in the upper atmosphere strengthens and remains over a region for several days up to several weeks.[8] This traps heat near the earth's surface. It is usually possible to detect heat waves by using forecasting instruments. This allows the authorities to issue a warning.
Heat waves have an impact on the economy. They can reduce labour productivity, disrupt agricultural and industrial processes and damage infrastructure.[9][10] Severe heat waves have caused catastrophic crop failures and thousands of deaths from hyperthermia. They have increased the risk of wildfires in areas with drought. They can lead to widespread electricity outages because more air conditioning is used. A heat wave counts as extreme weather. It poses danger to human health, because heat and sunlight overwhelm the thermoregulation in humans.
Impacts on the environment[edit]
Wildfires[edit]
A heat wave occurring during a drought can contribute to bushfires and wildfires. This is because a drought dries out vegetation, so it is more likely to catch fire. During the disastrous heat wave that struck Europe in 2003, fires raged through Portugal. They destroyed over 3,010 square kilometres (1,160 sq mi) of forest and 440 square kilometres (170 sq mi) of agricultural land. They caused about €1 billion worth of damage.[84] High end farmlands have irrigation systems to back up crops.
Floods[edit]
Heat waves can also contribute to flooding. Because hot air is able to carry more moisture, heatwaves may be followed by extreme rainfall especially in mid-latitude regions.[85] For example, the record-breaking heat wave that afflicted Pakistan beginning in May 2022 led to glacier melt and moisture flow. These were factors in the devastating floods that began in June and claimed over 1,100 lives.[86]
Wild animals on land[edit]
Researchers have predicted that roughly 10-40% of all land vertebrate species will be affected by heat waves by 2099, depending on the amount of future greenhouse gas emissions.[87] Heatwaves present an additional form of stress and evolutionary pressure for species that already deal with habitat loss and climate change.
Species have a thermal range of tolerance that describes the temperatures where they perform best. Temperature conditions that are outside of this range may experience decreased fitness and the inability to reproduce.[88][89] The species with sufficient genetic variation will be able to ensure some individuals can survive frequent days of high temperatures in the future.[90]
Oceans[edit]
Marine heatwaves may cause mass mortality in fish populations, especially for species that are better adapted to cooler temperatures.[91] Species that have adapted to warmer temperatures may expand their range during a heatwave. These invasive species may outcompete the native species that experience higher mortality during a heatwave, which disrupts ecosystem functioning.[91] Marine heatwaves have also been correlated with negative impacts on foundation species such as coral and kelp.[92]
Options for reducing impacts of heat waves on humans[edit]
A possible public health measure during heat waves is to set up air-conditioned public cooling centres. There are novel designs for cooling systems that are relatively low-cost. They do not use electrical components, are off-the-grid electrical power sources and the storage of solar energy chemically for use on demand.[93][94]
Adding air conditioning in schools[95] provides a cooler work place. But it can result in additional greenhouse gas emissions unless solar energy is used.
Society and culture[edit]
Policymakers, funders and researchers have created the Extreme Heat Resilience Alliance coalition under the Atlantic Council. This advocates for naming heat waves, measuring them, and ranking them to build better awareness of their impacts.[105][106]