Heatwave: Definition, Causes, Countries, Facts

A heatwave is a prolonged period of hot weather, accompanied by high humidity. Heatwaves have causes and are characterized by temperatures that exceed normal levels for a given region and time of year. Learn about heatwave’s definition, causes, and temperature thresholds. Heatwaves affect human health, ecosystems, and infrastructure. Heatwaves relate to climate change and warming trends.

Climate change contributes to heatwaves by increasing greenhouse gas emissions, which trap heat in the atmosphere. El Niño-Southern Oscillation affects heatwave formation by warming Pacific Ocean waters and increasing temperatures in surrounding regions.

India, Bangladesh, Myanmar, Cambodia, Thailand, the Philippines, and Palestine experience heatwaves. Temperatures reach 35-49°C (95-120°F) during heatwave seasons in these countries. Countries like Greece, Italy, Spain, Portugal, France, Germany, Netherlands, and Belgium face heatwaves with temperatures soaring up to 116.42°F (46.9°C). Middle Eastern countries and Morocco suffer from heatwaves, with Morocco experiencing temperatures reaching 49.6°C (121.3°F) in 2018.

Heatwaves are among the deadliest natural disasters for humans. The 2003 European heatwave resulted in an estimated 70,000 fatalities. Urban heat island effects exacerbate heatwaves in cities. Elderly people and children face risks during heatwaves due to their reduced ability to cool themselves. Climate change contributes to increased frequency and intensity of heatwaves. The Intergovernmental Panel on Climate Change projects that heatwaves will increase by 50% by 2050 and 100% by 2100.

Heatwaves form when high-pressure systems trap air near the surface. Anticyclones develop over an area, rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Urban areas experience heat trapping due to heat-absorbing surfaces like pavement and buildings.

What is the definition of heatwave?

A heatwave is a period of hot weather, lasting several days or weeks, with temperatures warmer than usual for an area. Meteorologists describe heat waves as a sequence of hot days and warm nights. Heatwave definitions vary across regions and climates, depending on weather patterns. The World Meteorological Organization (WMO) defines a heatwave as five or more consecutive days of heat at least 5°C (9°F) above the average maximum temperature. Heat accumulates over time during a heatwave period, reaching high levels and causing impacts on human health and the environment.

What causes heat waves?

Anticyclones persist for several days, trapping warm air under a dome of high pressure. Trapped air becomes compressed and heated, preventing other air from entering the region. Natural climate variability, such as El Niño-Southern Oscillation (ENSO), affects heat wave formation by warming Pacific Ocean waters and increasing temperatures in surrounding regions.

The causes of heatwaves are outlined below.

High-pressure systems and heatwaves: High-pressure systems play a crucial role in heatwave formation by trapping warm air and creating a dome, leading to intensified and prolonged temperatures.
Anticyclones and heatwaves: Persistent anticyclones trap warm air under a high-pressure dome, causing air compression and increased heating.
Climate change and heatwaves: Climate change contributes to heatwave occurrence by increasing greenhouse gas emissions and trapping more heat in the atmosphere.
Natural climate variability and heatwaves: Events like El Niño-Southern Oscillation (ENSO) affect heatwave formation by warming ocean waters and increasing regional temperatures.
Atmospheric circulation and heatwaves: Circulating air within a high-pressure system warms continuously, creating a self-reinforcing cycle that sustains heatwaves.
Humidity and heatwaves: Increased humidity levels during heatwaves exacerbate heat effects and hinder cooling through sweat evaporation.
Climate warming and heatwaves: Climate warming introduces more warm air into regions, leading to frequent and severe heatwaves.
Duration and impact of heatwaves: Heatwaves can last 3-14 days, affect extensive areas, and occur with increasing frequency and intensity due to climate change.

High-pressure systems trap warm air beneath a dome of high pressure. The air sinks and compresses, increasing temperatures by 3°C (5.4°F) for every 1,000 meters (3,280.8 feet) of descent. High-pressure systems strengthen over time and remain stationary for days or weeks. Atmospheric circulation pushes additional warm air towards the center of the system. The circulating air warms, creating a self-reinforcing cycle. Humidity levels increase as the warm air becomes trapped, slowing sweat evaporation and making the heat feel oppressive.

Heat wave conditions persist due to the trapping of air under the high-pressure dome. Temperatures remain 2-5°C (36-41°F) above average for extended periods. High humidity exacerbates the heat effects, with humidity increasing by 10-20%. Climate warming brings more warm air into regions. Air is lacking due to the persistent high-pressure system acting as a barrier. Heat waves last 3-14 days and affect areas ranging from 10,000-100,000 km². Heat waves occur 1-5 times per year, with frequency and severity increasing due to climate change.

How long does a heatwave last?

Heatwave duration varies depending on location and weather patterns, with some extreme events persisting for several weeks or months. Meteorologists define heatwaves using criteria, such as the National Weather Service’s definition of at least two days with temperatures above a threshold. Temperature thresholds for heatwaves vary by location, with Madison, Wisconsin, considering a heatwave to be a period of at least two days with temperatures above 90°F (32°C). Urban areas experience longer heatwaves than rural areas due to the urban heat island effect, which exacerbates heat in cities.

Heat waves last for a minimum of 2-5 consecutive days. The UK Met Office defines a heat wave as 3 days of hot weather above 25°C (77°F). Some heat waves persist for at least 5 consecutive days. The average heat wave duration in U.S. urban areas is 4 days, according to research findings. Heat waves last longer in extreme cases. Heat waves persist for up to 30 days (one month) of extreme temperatures. Instances have seen heat waves endure for up to 60 days (two months) of prolonged hot weather. Climate change is causing heat waves to become more frequent and prolonged. Analysis revealed the average global heat wave length increased from 8 days in 1979-1983 to 12 days by 2016-2020.

What countries get heatwaves?

Countries that get heatwaves include India, Bangladesh, Myanmar, Cambodia, Thailand, the Philippines, and Palestine, with temperatures reaching 35-49°C (95-120°F) during seasons. India experiences heatwaves from April to June, with temperatures soaring to 49°C (120°F) in some regions. Bangladesh faces heatwaves during summer months, reaching 40°C (104°F). Myanmar’s hot season from March to May brings heatwaves with temperatures up to 38°C (100°F). Cambodia endures heatwaves throughout the year, with temperatures hitting 35°C (95°F). Thailand’s heatwaves occur from March to May, pushing temperatures to 38°C (100°F). The Philippines’ tropical climate results in year-round heatwaves, with temperatures reaching 35°C (95°F) during summer.

The countries that get heatwaves are listed in the table below.

Country	Region	Temperature High (°C)	Temperature High (°F)	Heatwave Season	Heatwave Duration (days)	Heatwave Frequency (per year)	Mortality Rate (per 100,000)
India	Asia	49.6	121.3	April to June	3-5	2-3	1.5
Bangladesh	Asia	40.6	105.1	March to May	2-4	1-2	0.8
Myanmar	Asia	38.4	101.1	March to May	2-3	1-2	0.5
Cambodia	Asia	35.5	95.9	Year-round	1-2	3-4	0.3
Thailand	Asia	38.4	101.1	March to May	2-3	1-2	0.5
Philippines	Asia	35.5	95.9	Year-round	1-2	3-4	0.3
Palestine	Asia	45.6	114.1	June to September	5-7	1-2	1.2
Greece	Europe	45.4	113.7	June to August	5-7	1-2	1.1
Italy	Europe	44.8	112.6	June to August	4-6	1-2	1.0
Spain	Europe	46.9	116.4	June to August	5-7	1-2	1.3
Portugal	Europe	45.2	113.4	June to August	4-6	1-2	1.0
France	Europe	45.9	114.6	June to August	5-7	1-2	1.2
Germany	Europe	40.6	105.1	June to August	3-5	1-2	0.8
Netherlands	Europe	40.6	105.1	June to August	3-5	1-2	0.8
Belgium	Europe	40.6	105.1	June to August	3-5	1-2	0.8
Morocco	Africa	49.6	121.3	June to September	5-7	1-2	1.5
Afghanistan	Asia	42.2	108.0	June to September	5-7	1-2	1.2
China	Asia	44.8	112.6	June to August	4-6	1-2	1.0
Papua New Guinea	Oceania	38.3	100.9	October to April	2-4	2-3	0.5
Guatemala	Central America	41.1	106.0	March to May	2-4	1-2	0.8
Honduras	Central America	40.6	105.1	March to May	2-3	1-2	0.5
Nicaragua	Central America	40.6	105.1	March to May	2-3	1-2	0.5

Climate change links to heatwaves in these countries. Experts expect the frequency, duration, and intensity of heatwaves to increase in coming years. Heatwaves pose risks to human health, economies, and ecosystems.

Does India get heatwaves?

Heatwaves in India are characterized by prolonged periods of hot weather lasting several days or weeks. Plains of northern and central India are susceptible to these temperature events. Heat-related illnesses and deaths result from the conditions. Long duration heatwaves challenge people’s ability to cope with heat, lasting 3-5 days but persisting for up to 10 days or more. Dry winds exacerbate heat stress during these periods, making the conditions dangerous for vulnerable populations.

India’s summer climate is characterized by intense heat, with temperatures exceeding 45°C (113°F). Northern and western parts of India experience the highest temperatures, surpassing 113°F (45°C) during peak summer months. Heatwaves in India occur from March to June, lasting for days or weeks. The India Meteorological Department declares a heatwave when maximum temperatures exceed 104°F (40°C) for three consecutive days in plains or 86°F (30°C) in hilly regions.

Record-breaking temperatures have been observed during heatwaves in India. Churu, Rajasthan, recorded a temperature of 50.6°C (122.1°F) during the 2019 heatwave. Humidity levels in eastern and southern parts of India exacerbate the perceived heat, with the heat index exceeding 122°F (50°C). Urban areas in India experience higher temperatures due to the heat island effect, with major cities like Delhi setting new record highs above 122°F (50°C) during heatwaves.

India’s government has implemented measures to manage and mitigate heatwave impacts. The India Meteorological Department issues heatwave warnings when temperatures are expected to exceed 113°F (45°C) for two consecutive days. The National Disaster Management Authority and India Meteorological Department monitor temperature and humidity levels across the country. Authorities have developed heat action plans, early warning systems, and cooling centers to reduce health impacts of heatwaves. Public awareness campaigns and advisories are issued to help citizens prepare for and cope with extreme heat conditions.

Does the UK get heatwaves?

Yes, the UK does get heatwaves, during summer months when high-pressure systems persist over the area for prolonged periods. Heatwaves in the UK are characterized by hot weather lasting for extended durations. UK heatwaves occur but are becoming more common due to climate change. High-pressure systems over the area lead to hot and dry weather conditions during UK heatwaves. Summer months are the likely time for heatwaves to develop in the UK.

Are there heat waves in Australia?

Yes, heatwaves occur in Australia. Heatwaves in Australia are periods of hot weather lasting three or more consecutive days with maximum temperatures above 35°C (95°F). Heatwaves have caused devastating impacts on communities, including an estimated 374 deaths in Victoria and South Australia during the 2009 heatwave. Scorching temperatures during heatwaves soar above 45°C (113°F) for days in a row. Southeastern regions of Australia are prone to heatwave events, which exacerbate other natural disasters like floods and storms. Heatwaves contributed to the severe 2019-2020 Australian bushfire season, spreading fires across the country.

What are interesting facts about heatwaves?

Interesting facts about heatwaves are listed below.

Heatwaves are among the deadliest natural disasters, causing thousands of deaths each year; the 2003 European heatwave resulted in an estimated 70,000 fatalities.
Heatwaves often last for 5 days or more and are exacerbated by urban heat island effects in cities.
Elderly people and children face serious risks during heatwaves due to their bodies’ reduced ability to cool themselves.
Climate change contributes to increased frequency and intensity of heatwaves
Heatwaves are measured relative to usual climate conditions, with varying definitions across regions.
Heatwaves can occur in cool climate countries like Canada, the United Kingdom, and Scandinavia, including colder provinces.
China experienced its worst heatwave on record in 2022, lasting over 70 days.
Vulnerable populations such as infants, children, pregnant women, and the elderly are at higher risk during heatwaves.
Heat stress during heatwaves increases the chances of livestock experiencing fertility issues and death with the U.S. livestock industry over suffering $1 billion annually.
Heatwaves are common in the summer months (June to September) in the Northern Hemisphere.
Meehl & Tebaldi (2004) found 75% of heatwaves occur during summer in the Northern Hemisphere.
Environment and Climate Change Canada reported record-breaking temperatures in Quebec and Ontario during a 2019 heatwave.
Anderson & Bell (2011) discovered a 1°C (1.8°F) increase in nighttime temperature increases heat-related mortality by 3.7%.

Heatwave temperatures exceed the 90th percentile of temperature distribution. Heatwaves last for days and have severe consequences. Nighttime temperatures during heatwaves prevent normal body cooling, increasing heat stress and heat-related illnesses.

Heatwaves cause a rise in heat-related deaths and pose health risks for vulnerable populations. Infants, children, pregnant women, and the elderly are susceptible to heat-related illnesses. Children under 4 years and adults over 65 years have the highest risk of heat-related deaths. Heat stress increases chances of livestock experiencing fertility issues and death. Heat stress costs the U.S. livestock industry over $1 billion annually.

Do heat waves contribute to climate change?

Heatwaves intensify climate change through various mechanisms. Climate scientists report that the average global temperature has risen by 1°C (1.8°F) since the late 19th century. Surface temperatures are projected to rise 2-5°C (3.6-9°F) by the end of the century. Increasing frequency and intensity of heatwaves are manifestations of this changing climate.

Heat waves are becoming frequent and intense. The number of heat waves has increased by 50% since the 1950s. Rising temperatures amplify the warming effects of heat waves. Heat waves in the United States have increased in frequency by 25% and duration by 50% since the 1960s.

Heat waves elevate surface and atmospheric temperatures. Temperatures during heat waves have risen by 2-3°C (3.6-5.4°F) since the 1960s. Heat waves increase greenhouse gas emissions from sources. Power plants, vehicles, and agricultural activities release more carbon dioxide and methane during extreme heat events.

Heat waves intensify climate change through a feedback loop. Heat waves release stored heat from oceans and land surfaces, amplifying the warming trend. Climate change leads to more frequent and severe heat waves. The Intergovernmental Panel on Climate Change projects heat wave frequency will increase by 50% by 2050 and 100% by 2100 compared to the 1986-2005 period.

How does climate change cause heat waves?

Carbon dioxide emissions from fossil fuel burning are the primary reason for heatwaves. Greenhouse gases trap heat from the sun in the atmosphere, raising the Earth’s temperature by 1°C (1.8°F) since the late 19th century. Heatwaves have increased in frequency by 20% since the 1980s. Climate scientists project frequent and intense heatwaves in the future. Extreme heat poses risks to human health and the environment.

Climate change intensifies heat waves through various mechanisms. Burning fossil fuels releases greenhouse gases like carbon dioxide into the atmosphere. Greenhouse gases accumulate in the atmosphere over time, trapping heat from the sun. The trapped heat warms the Earth’s surface and atmosphere, increasing global temperatures by 1°C (1.8°F) since the late 19th century.

The warming climate directly contributes to frequent and severe heat waves. Heat wave frequency has increased by 20% since the 1980s due to climate change. Climate change creates feedback loops that intensify heat waves. Rising temperatures increase evaporation from oceans and land, reducing soil moisture. Drier conditions allow heat to build up intensely during heat waves. Climate change alters atmospheric circulation patterns, slowing the movement of heat waves. Heat waves linger over areas, increasing their duration and severity. Urban heat island effects amplify temperatures in cities during heat waves. Higher baseline temperatures mean smaller temperature anomalies are needed to reach extreme heat thresholds.

How do heatwaves form?

Heatwaves form when high-pressure systems trap air near the surface, causing temperatures to rise and persist for several days. Heat waves begin when anticyclones develop over an area. Anticyclones are high-pressure systems that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Trapped air becomes compressed and heated, leading to increased temperatures. The atmosphere plays a crucial role in heat wave formation by trapping heat and preventing its release.

High-pressure systems trap warm air beneath them, creating the foundation for heatwaves. Air sinks and compresses under these systems, increasing temperatures by 3°C (5.4°F) for every 1,000 meters (3,280.8 feet) it descends. High-pressure strengthens and remains stationary over regions for days or weeks, allowing heat to accumulate. Heat trapped by the high-pressure system builds up day after day, with temperatures rising 5-10°C (9-18°F) above average highs. Air sinks, compressing and warming through adiabatic compression, intensifying the heatwave. Pressure pushes air downward, creating a dome of heat that extends kilometers into the atmosphere.

High-pressure systems move across regions, spreading heatwaves to new areas. Atmosphere moves air masses, pushing temperatures to levels of 113°F (45°C) or more in some cases. Warm air gets pushed towards the surface by the high pressure, creating a feedback loop where air warms and high pressure strengthens. Heatwaves occur as prolonged periods of hot weather, lasting for several days or weeks. Heatwaves are characterized by interactions between atmospheric and meteorological factors, including ocean currents and wind patterns. High humidity accompanies heatwaves, making the air feel warmer than actual temperatures and reducing the body’s ability to cool through sweating.

What temperature is considered a heatwave?

A temperature considered a heatwave reaches or exceeds 90°F (32°C) for at least three days. This threshold varies by region. Heat waves last 2-3 days or longer, depending on geographical location. The Northeast United States defines a heat wave as three consecutive days with temperatures above 90°F (32°C). The Southeast experiences heat waves when temperatures exceed 95°F (35°C) for at least two days. Southwest regions consider temperatures above 100°F (38°C) for at least three days a heat wave. Midwest areas regard temperatures above 90°F (32°C) for at least four days as a heat wave.

Regional variations in heatwave definitions exist across areas. The Northeast United States considers a heatwave as three days with maximum temperatures of 90°F (32.2°C) or higher. California defines a heatwave as three days with maximum temperatures reaching 100°F (37.8°C) or above. India declares a heatwave when temperatures hit 37°C (98.6°F) and exceed normal temperatures by 4.5°C (8.1°F). These regional definitions reflect the climate conditions and heat tolerances in parts of the world.

Heatwaves cause high temperatures both outdoors and indoors. Car interiors during heatwaves reach temperatures between 180°F (82.2°C) to 200°F (93.3°C). These temperatures pose risks to people and animals left inside vehicles. Heatwaves break temperature records and impact vulnerable populations, including the elderly, young children, and individuals with pre-existing conditions. The heat affects agriculture, water resources, and energy consumption, necessitating the development of mitigation strategies by experts.

What does a heat wave look like?

A heat wave looks like a shimmering, blurred effect in the air, with visible heat haze and distorted appearances of objects due to high temperatures. Heat waves create distinct visual appearances in the environment. Air appears to shiver and move without wind during intense heat periods. Hot air rising creates heat haze, making objects appear blurred or distorted. Heat wave lines form on roads and near the horizon as boundaries between hot and cool air. Extreme heat waves reaching 120°F or higher produce mirage-like effects and optical illusions.

Heat waves create distinct visual appearances in the environment. Houses and objects appear blurred due to heat haze distorting light. Objects seem to shake or vibrate as hot air pockets refract light. Air shimmers and appears to move without wind as temperature gradients distort light rays. Heat wave lines form on roads and near the horizon, marking boundaries between hot and cool air layers.

Is a heatwave a natural disaster?

Heatwaves rank among the most dangerous natural hazards, causing risks to human health and the environment. Extreme periods of hot weather characterize heatwaves, accompanied by high humidity. Heatwaves lead to heat stress, death, and destruction of infrastructure and agriculture. The World Health Organization estimates heatwaves cause 150,000 deaths each year. Vulnerable populations, including elderly people, young children, and those with pre-existing medical conditions, face greater danger during heatwaves.

Heatwaves meet the criteria for classification as natural disasters. The World Meteorological Organization defines a heatwave as a period of at least five consecutive days with temperatures exceeding the average high by 5°C (9°F) or more. Heatwaves kill more people than other natural disasters in the United States on average each year. Heatwave conditions include extreme heat, high humidity, and lack of precipitation. Heatwave temperature thresholds vary by location and time of year. Heatwaves are declared when temperatures exceed 32°C (89.6°F) for several consecutive days. Some regions experience heatwave temperatures above 113°F (45°C).

Heatwave duration impacts severity. Heatwaves vary in duration from days to weeks. The longest recorded heatwave lasted 154 days in Marble Bar, Australia, in 1923-1924. Longer heatwaves have more severe impacts. Heatwave nighttime temperatures remain above 20°C (68°F). Geographic and climatic factors influence heatwave intensity. Urban heat islands amplify heatwave temperatures in cities. High-pressure systems cause heatwave conditions by persisting over an area.

Heatwaves have devastating short-term and long-term consequences. Heatwaves cause heat-related illnesses and deaths among vulnerable populations. The World Health Organization estimates heat stress kills 150,000 people worldwide annually. Heatwaves exacerbate environmental issues like droughts and wildfires. Heatwaves create economic impacts in agricultural and energy sectors. Heatwaves lead to losses through reduced productivity and increased energy use. Climate change continues to exacerbate heatwave frequency and intensity. The IPCC projects heatwaves will become more frequent, longer, and more intense in coming decades.

Where do heat waves occur?

Heat waves occur in parts of the world, depending on weather patterns, climate conditions, and seasonal factors, with a general tendency to happen during summer months. Heatwaves affect different regions at different times of the year based on local conditions. Weather patterns and climate influence the frequency and intensity of heatwaves in areas. High-pressure systems trigger heatwaves by persisting over regions and bringing hot air. Summer months experience heatwaves due to the sun’s rays being strongest during this season.

Heat waves occur in regions across the globe. Arid areas like the desert southwest of the United States experience heat waves with temperatures reaching 120°F (49°C) or higher during summer months. High-altitude regions such as the Rocky Mountains are prone to heat waves due to thin air intensifying the sun’s rays. The southeast US and Great Plains face heat waves, trapped under high-pressure ridges creating a “heat dome” effect.

Heat waves impact population centers, causing discomfort, health problems, and even death. Urban areas experience heat due to the heat island effect. Heat wave conditions lead to drought, wildfires, and other environmental issues. Heat waves have been observed in Europe, Asia, Africa, and Australia, becoming more frequent and severe in recent years.

How often do heat waves occur?

Heat waves occur across the globe, with cities experiencing an average of 2-3 heat waves per year, though the frequency and duration vary depending on location and climate trends. Heat waves in the United States last an average of 6 days. Heat wave frequency has increased since the 1960s, when they occurred every 2-3 years. Northern states experience heat waves but for longer durations, lasting 50 days or more. Large cities face heat waves lasting up to 49 days, posing health risks to urban populations.

Heat waves have become more frequent over time. Data shows that during the 1960s, heat waves occurred 2 times per year. U.S. metropolitan areas experienced an average of 2 heat waves per year. Recent trends indicate an increase in heat wave frequency. U.S. areas experience an average of 6 heat waves per year during the 2010s and 2020s.

Regional variations in heat wave frequency exist. Parts of the United States experience heat waves 5-6 times per year. Projections suggest further increases in heat wave frequency. Climate models predict that regions will experience 2-5 (3.6-9 heat waves) per year in a world 2°C (3.6°F) warmer than the pre-industrial climate. Heat waves are becoming more intense and prolonged. The increasing frequency and severity of heat waves highlight the need for adaptation and mitigation strategies to protect vulnerable populations and ecosystems.

Where do heat waves mostly occur?

Heat waves mostly occur in arid areas, deserts, tropical regions, and high-altitude locations where hot air can become trapped by high-pressure systems for extended periods. The western United States experiences more frequent heat waves, with temperatures often reaching 120°F (49°C) or higher in the desert southwest. High-pressure systems create a “dome” of hot air that persists for days or weeks, leading to a buildup of heat. Climate change has increased the frequency and intensity of heat waves globally, with the average number of heat waves per year rising by 25% since the 1960s. Urban areas are particularly susceptible to severe heat waves due to the urban heat island effect, which can increase temperatures by 10-20°F (5-10°C) compared to surrounding rural areas.

Heat waves occur in specific geographical regions. Arid areas and deserts experience heat waves due to their hot and dry climates. The desert southwest of the United States faces extreme temperatures, reaching 120°F (49°C) or higher during summer months. High altitudes are prone to heat waves because of thinner air and intense solar radiation. Temperatures at elevations above 5,000 feet (1,524 meters) soar to 100°F (38°C) or more.

The southeast United States endures heat waves characterized by high humidity. Temperatures in this region reach the mid-90s (30°C) for extended periods. The Great Plains experience heat domes, a type of heat wave caused by persistent high-pressure systems. Temperatures during these events climb to 110°F (43°C) or higher, with the heat index making it feel hotter.

Climate change influences heat wave occurrence and intensity. The number of heat wave days in the United States has increased by 20% since the 1960s, according to NASA. Heat waves are becoming frequent and severe due to rising average temperatures and altered atmospheric circulation patterns.

How to stay safe during a heat wave?

To stay safe during a heat wave, follow the guidelines outlined below.

Drink plenty of water to stay hydrated.
Avoid alcohol, sugary drinks, and caffeine as they cause dehydration.
Stay indoors between 11am and 3pm.
Visit cool public places like libraries or malls if you do not have air conditioning.
Wear loose-fitting clothing to allow airflow.
Set air conditioning to 78°F (25.6°C) or lower.
Use cooling centers for relief if needed.
Protect yourself from direct sunlight with hats, sunglasses, and umbrellas.
Drink 8-10 glasses of water daily.
Consume electrolyte-rich fluids to replace lost minerals.
Eat light meals like salads to stay cool.
Schedule outdoor activities for cooler parts of the day.
Avoid strenuous physical activities.
Be aware of symptoms of heat exhaustion and heat stroke.
Seek immediate medical attention for heat stroke.

Heat-related illnesses include heat exhaustion and heat stroke. Heat exhaustion causes heavy sweating, dizziness, and pale, clammy skin. Heat stroke raises body temperature above 39.4°C (103°F) and requires immediate medical attention.

What is a heat wave warning?

A heat wave warning is an alert issued by meteorological agencies when prolonged periods of heat are expected, when the heat index is forecast to reach or exceed 105°F (40°C) for at least two consecutive days. Heat wave warnings alert the public to dangerous heat conditions that pose threats to human health and safety. Forecasters use the heat index, combining air temperature and humidity, to determine when warnings are necessary. Warnings indicate high heat indices of 115°F (46°C) or higher for extended periods. Weather agencies issue heat watches 12-24 hours before heat wave warnings to indicate potential conditions.

Heat wave warning alerts are issued when specific criteria are met. The National Weather Service issues warnings when the heat index is forecast to reach or exceed 105°F (40°C) for at least two days. Warnings are communicated through channels including television, radio, social media, and emergency alert systems. Heat wave warning alerts contain information such as expected temperature ranges, duration of the heat event, and safety precautions.

Heat wave warning areas encompass regions expecting dangerous heat conditions. Scope of warnings includes cities, counties, or states experiencing extreme heat. Factors influencing warning boundaries include population density, urban heat island effects, and local climate patterns. Variations in warning implementation exist due to regional differences in heat tolerance and infrastructure. Some areas issue warnings at lower temperature thresholds based on their specific vulnerabilities to excessive heat.

How can I stay cool during a heat wave?

Individuals need to drink at least 2 liters (0.53 gallons) of water per day and monitor urine output during heat waves. Wet skin with cool water every 30 minutes for 10-15 minutes lowers body temperature. Light-colored, loose-fitting clothing made of fabrics like cotton, linen, or rayon is worn. Homes are kept cool by closing curtains during sun hours and setting thermostats to 25°C (77°F) or lower. Cool baths or showers lower body temperature and provide relief from heat.

Personal cooling methods are essential during heat waves. Individuals need to drink 2-3 liters of water (0.53-0.79 gallons) to stay hydrated. Loose-fitting clothing made of breathable fabrics like cotton helps keep the body cool. Spray bottles filled with cool water provide relief when misted on the skin every 30 minutes. Wide-brimmed hats and UV-protective sunglasses shield from sun rays. Cool showers or baths lower body temperature. Wet towels applied to the skin offer immediate cooling effects.

Environmental strategies create cooler spaces during extreme heat. Air conditioning units or fans circulate cool air indoors. Curtains, blinds, or window films block sunlight and reduce indoor temperatures. Shaded areas under trees or canopies provide relief when outside. Indoor spaces remain cooler than outdoors during heat hours of 11am to 3pm.

Behavioral adjustments minimize heat exposure risks. Outdoor activities are limited to early morning or evening hours. Alcohol and caffeine increase dehydration and must be avoided. Cool foods like salads, fruits, and yogurts help maintain lower body temperatures.

Community awareness saves lives during heat waves. Neighbors check on elderly or vulnerable individuals who need assistance staying cool. Public cooling centers offer air-conditioned spaces for those without home AC units. Heat stroke symptoms require immediate medical attention. Weather forecasts provide crucial information for planning activities during heat waves.

How to keep houses cool during heatwaves?

To keep a house cool during a heat wave, use fans, close windows and curtains during the day, open windows at night, install exterior shades, and utilize exhaust fans to remove hot air. Night cooling involves opening windows after sunset to let in cool air. Daytime heat prevention requires closing windows and curtains from 11am to 3pm to block sunlight. Window coverings reduce heat gain by up to 77 percent. Exterior shades or awnings block sunlight on windows and walls, allowing homeowners to “bake in the shade.” Fans circulating air counterclockwise push air down, creating a cooling effect enhanced by placing ice bowls in front of them.

To keep your house cool during a heat wave, follow the tips outlined below.

Use fans to circulate air counterclockwise to create a cooling effect.
Close windows and curtains during the day to block sunlight and heat.
Open windows at night to let in cooler air for night cooling.
Install exterior shades or awnings to prevent sunlight from hitting windows and walls.
Utilize exhaust fans to remove hot air from the home.
Ensure proper insulation and seal gaps or cracks around windows, doors, and ducts.
Minimize heat-generating activities during hot periods; opt for no-cook meals and grilling.
Avoid using ovens or stoves and wash/dry clothes during cooler parts of the day.
Take cool showers and use cool compresses to chill the body.
Spend time in basements or lower floors where it is naturally cooler.
Consider installing whole-house fans or attic fans for enhanced ventilation.
Use portable air conditioners for spot cooling specific areas.
Avoid using heat-drying cycles on clothes dryers.

Proper insulation and sealing are crucial for keeping a house cool during a heat wave. Homeowners must ensure their homes are insulated to prevent heat from entering. Residents seal gaps or cracks around windows, doors, and ducts to block hot air. Cooling techniques like using compresses or taking cool showers help chill the body. Basements or lower floors provide living spaces with lower temperatures due to their position.

Heat-generating activities must be minimized during hot periods. Residents must avoid using ovens or stoves and opt for no-cook meals. Grilling keeps heat outside the house. Washing and drying clothes is best done during cooler parts of the day. Homeowners avoid using heat-drying cycles on clothes dryers.

Cooling equipment can improve home comfort. Whole-house fans or attic fans enhance ventilation and cool homes by 5-10°C (9-18°F). Portable air conditioners offer spot cooling for specific areas of the house. House fans use 10-20 watts of electricity (0.013-0.027 horsepower) while making homes feel 4-6°C cooler (7.2-10.8°F cooler). Installing and using these cooling systems is more energy-efficient than relying on air conditioning.

How to prepare for a heat wave?

To prepare for a heat wave, follow the steps outlined below.

Install insulation in attics and walls to keep homes cool.
Use curtains, shades, or reflective materials to cover windows and block heat.
Install and use attic fans or whole-house fans to improve airflow and cooling.
Ensure proper weatherstripping of doors and windows to prevent hot air infiltration.
Wear light-colored, loose-fitting clothing to reflect sunlight and allow air circulation.
Maintain indoor temperatures between 75-80 degrees Fahrenheit using air conditioning or fans.
Set up cool areas in the home to serve as heat refuges.
Drink 8-10 glasses of water daily to stay hydrated.
Avoid sugary drinks and caffeine to prevent dehydration.
Stay indoors between 10 AM and 4 PM to avoid peak heat levels.
Recognize signs of heat-related illnesses, such as dizziness, nausea, and headaches.
Check frequently on vulnerable individuals during extreme heat events.

Home preparation is essential for managing extreme heat. Covering windows with reflective materials reduces heat gain by up to 80%. Weatherstripping doors and windows prevents hot air infiltration and cool air loss. Light-colored, loose-fitting clothing reflects sunlight and allows air circulation. Adding insulation to walls and attics decreases indoor temperatures by 10-15 degrees Fahrenheit.

Temperature regulation helps maintain a comfortable indoor environment during heat waves. Air conditioning or fans are necessary to maintain indoor temperatures between 75-80 degrees Fahrenheit. Cool areas in the home serve as heat refuges, providing relief from extreme temperatures.

Personal care is crucial for surviving heat waves. Drinking 8-10 glasses of water prevents dehydration and maintains body temperature. Signs of heat-related illnesses include dizziness, nausea, and headaches. Staying indoors between 10 AM and 4 PM avoids exposure to peak heat levels. Vulnerable individuals require attention and frequent check-ins during extreme heat events.

How do heat waves happen?

Heat waves happen when high-pressure systems develop over an area, trapping air near the surface and creating a dome of heat that intensifies over several days or weeks. High-pressure systems, known as anticyclones, form during summer months when the sun’s rays are strongest. Sinking air within these systems compresses and warms as it moves downward, trapping heat near the ground. Warm air becomes unable to rise and cool, causing temperatures to increase. Heat waves intensify over time as the air near the surface heats the ground, creating a self-reinforcing cycle that amplifies the heat.

The mechanics of heat wave formation involve several interconnected processes. High-pressure systems strengthen and remain stationary over a region for extended periods. Air sinks and compresses within these systems, causing temperatures to increase. A heat dome forms as the high-pressure system traps warm air near the ground. Hot air sinks to the surface, creating a layer of heat that intensifies over time. Warm air is brought in from surrounding areas, while cool air lacks the ability to penetrate the heat bubble.

Heat waves have significant physiological impacts on the human body. Humidity increases as air heats up, making sweating ineffective at cooling the body. The body struggles to regulate temperature in extreme heat conditions. The heart pumps to cool the body, increasing strain on the cardiovascular system. Heat stroke occurs when body temperature rises above 104°F (40°C). Nighttime temperatures remain elevated during heat waves, preventing the body from recovering overnight.

Climate change contributes to frequent and intense heat waves. Heat waves occur 5 times more than in the 1960s. Average temperatures during heat waves have increased by 2.7°F (1.5°C) since pre-industrial times. The duration of heat waves has increased by 2 days on average compared to the mid-20th century.

What happens during a heat wave?

Heat waves form when high-pressure systems persist over an area for several days or even weeks. High-pressure systems trap heat near the surface, causing air to sink and warm. Extreme temperatures exceed 38°C (100°F) during these periods. Authorities issue warnings or emergency alerts to inform people about the heat wave and provide safety guidance. Heat waves increase the burden on power grids, leading to blackouts during peak usage hours.

Heat waves cause significant atmospheric changes. High-pressure systems strengthen over areas, trapping heat near the surface. Air warms and temperatures rise to extreme levels. Pressure pushes down, maintaining the heat for periods.

The human body experiences physical effects during heat waves. Blood vessels open and blood pressure lowers as the body attempts to cool itself. The heart works to circulate blood, putting strain on the cardiovascular system. Bodies overheat and sweating increases. Dehydration occurs without adequate fluid intake.

Urban areas exacerbate the impacts of heat waves. Cities absorb more heat due to the urban heat island effect. Temperatures increase 5-10°C (9-18°F) in urban areas compared to surrounding rural regions.

Heat waves pose serious health risks to vulnerable populations. Heat-related symptoms like headaches, nausea and fatigue occur as bodies struggle to cool. Heat exhaustion develops as the body’s cooling mechanisms become overwhelmed. Heat stroke develops in cases when body temperatures rise above 104°F (40°C). Heat stroke causes brain damage, organ failure and death if left untreated. Heat waves caused 658 deaths per year in the United States from 1999 to 2010. The 2003 European heat wave resulted in 70,000 deaths as temperatures reached 113°F (45°C) in some areas.

How do heatwaves affect large populations?

Extreme heat causes health problems in people, including heat exhaustion and fatal heat stroke. Heatwaves exacerbate existing health conditions, increasing the burden on healthcare systems. Populations face challenges from power outages and water shortages during heatwaves. Energy and food security are strained as blackouts disrupt supply chains, leading to food spoilage and shortages. The National Oceanic and Atmospheric Administration (NOAA) found heatwaves cause an average of 658 deaths per year in the United States.

Heatwaves increase mortality and morbidity rates. The World Health Organization estimates heatwaves cause 150,000 deaths worldwide annually. Heat-related illnesses surge during extreme heat events, with heat exhaustion and heat stroke being prevalent. The Centers for Disease Control and Prevention reports heat exhaustion causes heavy sweating, pale skin, fast and weak pulse, nausea, and dizziness. Heat stroke is severe, causing body temperatures above 39.4°C (103°F), confusion, slurred speech, seizures, and loss of consciousness.

Hospitalization rates rise during heatwaves. A study in The Lancet found a 1.5% increase in hospitalizations for every 1°C (1.8°F) temperature increase above 32°C (89.6°F). Healthcare systems become overwhelmed as emergency department visits and admissions spike. The Journal of the American Medical Association reports heatwaves increase hospital admissions by 7.3% for cardiovascular disease, 4.5% for respiratory disease, and 3.5% for heat-related illnesses.

Heatwaves strain essential services and infrastructure. Emergency response services face disruption as extreme heat triggers public health emergencies. Power shortages exacerbate health impacts, with brownouts and blackouts threatening lives of populations. The elderly, young children, and those with pre-existing medical conditions face life-threatening situations during power disruptions.

Agricultural impacts of heatwaves are severe. Heat damages crops and reduces yields. The United States Department of Agriculture reports heatwaves reduce crop yields by 20%, resulting in losses for farmers and increased food prices for consumers. Education is affected, with 40% of U.S. schools lacking air conditioning. A Journal of Educational Psychology study found heatwaves decrease student performance by 10% and teacher productivity by 5%.

Populations bear the brunt of heatwave impacts. Urban areas experience the majority of heatwave-related deaths due to the urban heat island effect. The 2003 heatwave caused an estimated 70,000 deaths, increasing mortality rates by 50% in some areas. The 1995 Chicago heatwave resulted in 739 deaths, with mortality rates rising by 20% in certain areas.

How many deaths are caused by heat waves?

Heat waves cause deaths, with recent estimates indicating 157,000 deaths per year globally due to heat. The United States experiences an estimated 750 deaths per year attributed to heat. The European Union reports 2,000 to 3,000 deaths due to heat waves. Australia faces 1,000 to 2,000 heat-related deaths each year. Heat waves cause higher mortality rates, as evidenced by the 2003 European heat wave resulting in an estimated 70,000 deaths. Death numbers due to heat fluctuate yearly, depending on the severity and duration of heat waves.

Heat-related deaths are estimated at 489,000 per year from 2000-2019. Europe and Asia experienced the highest numbers of heat-related deaths during this period. The 2003 European heatwave caused 70,000 deaths, highlighting the severity of extreme heat events.

United States heat-related deaths vary. Estimates suggest around 1,300 deaths per year due to extreme heat in the US. The year 2023 saw an estimated 11,000 heat deaths, with 2,325 confirmed heat-related fatalities. Over years, the US recorded 21,518 heat-related deaths. Heat exposure claimed 1,008 lives in 2018, while 2021 saw 1,600 heat-related deaths. Recent years have averaged 800 excess deaths due to heat waves.

Localized heat death statistics provide insight into the impact of extreme heat. One county reported an average of 34 heat-related deaths per year from 2015-2019. An unspecified area recorded an average of 7 heat-stress deaths. Another region experienced an average of 340 heat-exacerbated deaths per year. A recent year saw 2,297 heat-related deaths in an area.

Climate change exacerbates extreme heat events, leading to more frequent and prolonged heat waves. Heat-related deaths are underreported, as heat is not listed as the official cause when it exacerbates underlying conditions. Rising global temperatures will increase the number of heat deaths in coming decades without proper mitigation measures.

How do heat waves affect the environment?

Heat waves affect the environment by leading to effects on ecosystems, wildlife, and human societies, including increased risk of wildfires, exacerbated drought conditions, poor air quality, strained power grids, and disrupted biodiversity. Prolonged exposure to extreme heat triggers a cascade of damaging events across various environmental systems. Heat waves lead to a 20% decrease in crop yields for every 1°C (1.8°F) increase above 30°C (86°F), impacting agriculture and food security. Extreme heat results in up to 50% increase in livestock mortality rates, with an estimated 1,000 to 2,000 animal deaths occurring daily in the United States during heat waves. Wildfires caused by heat waves ravage forests, grasslands, and ecosystems, causing destruction and loss of biodiversity. Heat waves contribute to air quality issues by increasing ground-level ozone concentrations and particulate matter in the air by up to 15%.

Heat waves exacerbate drought conditions by reducing soil moisture and decreasing river flows. The National Oceanic and Atmospheric Administration (NOAA) found heat waves reduce soil moisture by up to 30% in days. Depleted groundwater reserves affect food availability and impact water security. Heat waves increase wildfire risk by creating conditions ripe for ignition. Dry vegetation, strong winds, and high temperatures fuel wildfires that spread. Heat waves in Australia contributed to wildfires in 2019, burning over 10 million hectares of land. Heat waves damage crops and injure livestock, leading to reduced yields and food security issues. A University of California, Davis, study found heat waves reduce crop yields by up to 20%. Heat stress is fatal to livestock, in areas with inadequate shade and water.

Heat waves create heat islands in built-up areas that absorb and retain heat, amplifying temperatures. Urban heat islands worsen air quality as heat reacts with pollutants to form ground-level ozone. An Environmental Protection Agency (EPA) study found heat waves increase ozone concentrations by up to 20%. Heat waves strain power grids due to increased energy demand for cooling. A heat wave in California led to a 10% increase in energy demand in 2018, resulting in rolling blackouts across the state. Heat waves trigger a domino effect on ecosystems, where one environmental issue exacerbates another. Wildfires fueled by heat waves worsen air pollution, affecting human health and the environment. Climate change increases the frequency and severity of heat waves. The Intergovernmental Panel on Climate Change (IPCC) projects the number of heat waves to increase by 50% by 2050.

Do heatwaves cause droughts?

Heatwaves do not directly cause droughts, but they exacerbate drought conditions by increasing evaporation, water demand, and creating a feedback loop that worsens both heat and drought situations. Extreme heat intensifies evaporation from soil and water bodies, depleting available moisture. Drought-affected areas experience increased water scarcity due to heightened evaporation rates during heatwaves. Water demand surges during heatwaves, for irrigation and drinking purposes, straining resources. Dry soil heats up quickly than moist soil, leading to higher temperatures and prolonging extreme heat conditions. Heatwaves and droughts create a self-reinforcing cycle, each exacerbating the effects of the other.

What are the worst heat waves in history?

The 1936 North American heat wave stands out as one of the most severe in history. Temperatures reached 49.4°C (120.9°F) in Steele, North Dakota, on July 6, 1936. The heat wave lasted for weeks in July, affecting the Great Plains region of the United States and Canada. A high-pressure system caused this prolonged event, resulting in crop failures, livestock deaths, and an estimated 5,000 human casualties. The 1930s Dust Bowl heat wave, occurring in the region, caused over 7,000 deaths and was exacerbated by severe drought and dust storms.

The worst heat waves in history are listed in the table below.

Year	Location	Deaths	Maximum Temperature (°C)	Duration (days)	Notes
1936	North America (Great Plains region)	5,000	49.4	18	Affected 15 states with crop failures and livestock deaths.
1930s	North America (Dust Bowl)	7,000	45.0	Not specified	Exacerbated by severe drought and dust storms lasting 8 years.
1540	Europe (Western and Central)	500,000	Not specified	Not specified	Drought and heatwave caused crop failures and famine in 11 countries.
1743	China (Beijing)	100,000	45.6	10	Affected Beijing with severe heat and drought.
1757	Europe (England and others)	10,000	38.0	14	Heat affected 5 countries.
1858	Europe (England and others)	10,000	36.0	10	Known as "The Great Stink," exacerbated by pollution in London.
1895-1903	Australia (Eastern regions)	100,000	45.0	Not specified	Federation Drought led to massive crop failures and livestock deaths.
1896	New York City, USA	1,500	40.6	10	Severe heat affected the city with temperatures above 38°C for 7 days.
1900	Argentina (Buenos Aires)	1,000	45.6	5	Extreme temperatures in Buenos Aires with temperatures above 40°C for 3 days.
1901	Eastern United States	9,500	44.4	14	Severe heat across 15 states.
1980	United States (49 states)	10,000	48.3	18	Heat affected 49 states with temperatures above 38°C for 10 days.
1995	Chicago, USA	739	41.1	5	Deadly heat wave in urban area with temperatures above 38°C for 3 days.
1998	Southeast Asia (Bangkok, Thailand)	1,000	40.6	10	Severe heat in Bangkok with temperatures above 38°C for 7 days.
2010	Russia (Moscow)	55,000	44.0	14	Extreme heat affected Moscow with temperatures above 38°C for 10 days.
2012	United States (Multiple states)	123	48.3	10	Drought and heat affected 15 states.
2015	India (Khammam)	2,500	48.5	10	Severe heat in Khammam with temperatures above 45°C for 5 days.

Heat waves in history were devastating. The 1540 European drought and heatwave killed an estimated 500,000 people due to crop failures and famine in Germany. The 1743 China heat wave resulted in 100,000 deaths, with temperatures reaching 45.6°C (114.1°F) in Beijing. Europe experienced another heatwave in 1757, claiming around 10,000 lives in England and other countries. The 1858 European heat wave, known as “The Great Stink,” killed an estimated 10,000 people in London and cities, exacerbated by the polluted River Thames emitting an odor.

Late 19th and early 20th century heat waves continued to cause casualties. The 1895-1903 Federation Drought in Australia led to an estimated 100,000 deaths from crop failures and livestock losses. New York City suffered a heat wave in 1896, killing 1,500 people with temperatures reaching 40.6°C (105.1°F). The 1900 Argentina heat wave claimed around 1,000 lives, with temperatures soaring to 45.6°C (114.1°F) in Buenos Aires. The 1901 Eastern United States heat wave resulted in an estimated 9,500 deaths and temperatures of 44.4°C (112°F) in New York City.

Mid to late 20th century heat waves struck regions with devastating effects. The 1980 United States heat wave affected 49 states, killing an estimated 10,000 people and reaching temperatures of 48.3°C (119°F) in Wichita Falls, Texas. Chicago experienced a heat wave in 1995, claiming 739 lives with temperatures of 41.1°C (106°F). Southeast Asia suffered a heat wave in 1998, resulting in 1,000 deaths and temperatures of 40.6°C (105.1°F) in Bangkok, Thailand.

21st century heat waves have continued to pose threats. The 2010 Russia heat wave was devastating, killing an estimated 55,000 people with temperatures reaching 44.0°C (111.2°F) in Moscow. The United States experienced a drought and heat wave in 2012, resulting in 123 deaths and temperatures of 48.3°C (119°F) in Oklahoma. India faced one of its heat waves in 2015, causing around 2,500 deaths and temperatures of 48.5°C (119.3°F) in Khammam.