Blog 14| Date: 23rd April, 2024
As summer sets in, a fierce visitor knocks on our doors: the heatwave. Picture this: streets sizzle under the blazing sun, making you doubt if it's real or just a mirage. But there's more to this hot spell than meets the eye. Join me on a journey through the heatwave saga, where I will unravel the science, share survival tips, and explore how our changing climate plays a role. Let's dive in and beat the heat together!
What is heatwave?
Heatwaves aren't one-size-fits-all. Definitions vary depending on location, weather, and societal impact.
According to World Meteorological Organization, “a heatwave can be defined as a period where local excess heat accumulates over a sequence of unusually hot days and nights”.
As per National Oceanic and Atmospheric Administration (NOAA) in USA, “heatwave, also called hot wave or warm wave, is a period of abnormally and uncomfortably hot and usually humid weather. To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks”.
The UK Met Office defined heatwave as, “an extended period of hot weather relative to the expected conditions of the area at that time of year, which may be accompanied by high humidity”. In the UK, determining the occurrence of a heatwave relies on the concept of a heatwave threshold. This threshold is reached when a location experiences a span of at least three consecutive days, during which the daily maximum temperatures meet or surpass the designated heatwave temperature threshold. The threshold varies by UK county as seen in the UK temperature threshold map below:
Figure 1. Difference in heatwave threshold across UK (Source: UK Met Office)
Finally, the Indian Meteorological Department defines heatwaves as temperatures increasing by at least 5‒6 °C above the normal temperature.
Formation of Heatwave
Heatwaves occur when a dome of high-pressure air settles high in the atmosphere, typically between 10,000 to 25,000 feet, and stubbornly remains in place. This phenomenon causes the descent of hot air. Reports indicate that for every 100 meters the air descends, the temperature increases by approximately 1°C. As the hot air sinks, it forms a bubble-like barrier that traps heat close to the Earth's surface. This barrier acts as a seal, preventing the formation of convection currents that would typically lead to cloud formation and eventually rain clouds, which could help to cool the affected area. Instead, the consequence is a heatwave characterized by both high temperatures and high humidity at ground level. These heatwaves can persist for several days to weeks, exacerbating the conditions of intense heat and humidity.
Figure 2. Formation of heatwave. High-pressure systems can create a 'cap' that traps air in one place as it warms. This can lead to a heat wave (Source: SciJinks)
Recent Trends of Heatwaves
Over 70 days: In 2022, China experienced its most severe heatwave on record, lasting for more than 70 days.
30 times: Climate change amplified the severity of heatwaves in India and Pakistan in 2022, making them 30 times more likely to occur.
40.3°C: The UK witnessed record-breaking heatwaves in 2022, with temperatures reaching 40.3°C, surpassing the previous national record of 38.7°C.
220 million: In 2018, over 220 million vulnerable individuals were exposed to the impacts of heatwaves.
65 and older: Heat poses significant risks to vulnerable populations, including the elderly, pregnant women, infants, outdoor workers, and athletes.
5°C to 10°C: Urban areas can experience temperatures up to 5°C to 10°C higher than surrounding regions, intensifying the effects of heatwaves and associated risks.
Reference
Direct Energy. Heat Wave Information—Natural Disaster Guide. Retrieved April 23, 2024, from https://www.directenergy.com/learning-center/heatwave
Earth Science Data Systems, N. (2022, January 6). Heat Wave | Earthdata. Earth Science Data Systems, NASA. https://www.earthdata.nasa.gov/topics/atmosphere/weather-events/heat-wave
Jack McKenna. (2023, June 28). How Heatwaves Work and Why We’re Expecting More. MDPI Blog. https://mdpiblog.wordpress.sciforum.net/2023/06/28/how-heatwaves-work/
NOAA SciJinks. What Is a Heat Wave? | NOAA SciJinks – All About Weather. Retrieved April 23, 2024, from https://scijinks.gov/heat/
UK Met Office. What is a heatwave? Met Office. Retrieved April 23, 2024, from https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/temperature/heatwave
WMO. (2023, March 10). Heatwave. World Meteorological Organization. https://wmo.int/topics/heatwave
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