What Causes a Heat Wave to Happen?

By Giulia Graziati, Writer. May 4, 2023
What Causes a Heat Wave to Happen?

A heat wave can be generally defined as a period of prolonged hot weather which is excessive for a given climate. They are among some of the most devastating weather events, especially because their nature means they occur over a prolonged period of time. A consensus agreement has not yet been reached on the exact definition of a heat wave, but there are certain characteristics which can help us to define them.

At thedailyECO, we do this by asking what causes a heat wave to happen? We provide a general definition of a heatwave, as well as the effects it can have on ecosystems.

What are heat waves?

According to the World Health Organization (WHO) and the World Meteorological Organization (WMO), there is no consensus on a precise definition of a heat wave . It can be understood as a prolonged period of extremely hot weather which is either dry or humid. It can occur during the day or night and begins and ends abruptly. The duration of a heat wave is generally given to be a minimum of 2-3 days.

In this way, we can provide a basic definition of a heatwave as the following:

an extreme weather event with high temperatures that persist for several days in a specific geographic location.

Heat waves not only imply a considerable increase in temperature, but also bring with them a series of health and economic problems for societies. The reports made by the experts of the Intergovernmental Panel on Climate Change (IPCC) have shown the frequency of heat waves has increased considerably in the last 50 years. This problem is not a mere coincidence, since climate change is contributing to the intensification and periodicity of heat waves throughout the world.

Spain and Portugal experienced a severe heat wave in 2022 which made international news. As you can see in the photo below, the temperatures were very high throughout the countries.

What Causes a Heat Wave to Happen? - What are heat waves?
Image: Highs scheduled for Friday, June 17, 2022. Source:

What temperature constitutes a heat wave?

Although heat waves are becoming more relevant today, this does not mean that they did not exist in the past. These extreme weather events could have gone unnoticed because they occurred in little-known regions with few inhabitants and where records have been scarce or null.

According to numerous studies, the year 2021 was characterized by the increased occurrence of episodes of extreme weather and climate phenomena. Events such as heat waves and droughts became serious issues in different regions of the globe.

The presence of extreme temperatures are associated with the increase in the average temperature of the planet. The average annual temperatures recorded were above normal in most of the world, except for regions such as Alaska or Siberia. Heat waves in Europe, North Africa, South Asia and South America have exhibited abnormal temperature values in the year 2021.

  • In Europe there were thirteen daily high temperature records, being the ninth warmest year since records begam. In 2017, heat waves in Spain caused extreme temperatures and thermometers marked 47.2 °C in the city of Córdoba.

  • In June 2021, a heat wave hit North America making it its seventh warmest year on record. In Canada, the city of Lytton broke a national temperature record of 49.6 °C.

  • 2021 was the sixth warmest year ever recorded in South America. During the summer of 2023, Argentina suffered one of its harshest summers in which extreme heat lasted from February 28 to March 20 of that year, reaching almost 41 °C.

  • The year 2021 tied 2019 for the third warmest year on record in Africa and Asia had the seventh warmest year on record.

Learn more about the difference between weather and climate.

What Causes a Heat Wave to Happen? - What temperature constitutes a heat wave?

What causes heat waves to happen?

Now we know that heat waves are increasing on a global scale, it is important to know what is causing these record temperatures.

  • Natural variations: natural climactic changes can result in heat waves. These include the decrease of dry air that warms up and invades certain regions, greater solar radiation due to the absence of cloudiness, and hot and humid air entering without winds.

  • Climate change: the increase in temperature due to global warming generated by a greater percentage of greenhouse gas emissions is intensifying the frequency and presence of heat waves throughout the world. Learn more about how climate change is affecting our world's ecosystems with our guide to types of environmental impact.

  • Urbanization: urbanization and change in land use can increase the temperature in cities. This can generate something known as ‘urban heat islands’ in which asphalt-based buildings accumulate a large amount of heat during the day, causing the rise in temperature.

  • Change in land use patterns: change in land use patterns, such as deforestation, desertification and the entire transformation of natural ecosystems to farmland or livestock, can contribute to the formation of heat waves by alter the reflectivity and absorption patterns of the Earth's surface.

Effects of heat waves

Heat waves are a risk to our environment, but the problem is much greater than sweat stains on our clothes or a clammy day. Here are some of the most important consequences and effects of heat waves:

  • Increase in vector-borne diseases: warmer weather will increase the reproduction and distribution of vector-borne diseases.

  • Higher mortality in at-risk groups: children, the elderly and people with certain pathologies that put them at risk will be more exposed to these extreme weather events, increasing the mortality rate.

  • Decreased work capacity: risk of heat exhaustion, cardiac arrest, and more frequent workplace accidents for those who work outdoors.
  • Decrease in agricultural production: due to the drop in food production and less access to resources. The increase in temperature, the lack of rainfall reduce agricultural production.

  • Energy collapse: the use of air conditioners and fans generated a considerable increase in the demand for electricity related to the high temperatures, producing a greater energy demand overall.

  • Risks of forest fires: due to the drought due to the lack of precipitation and the extreme heat, the ecosystems present a high risk of fires. Take a look at our related article to learn how to helps top wildfires.

  • Biodiversity risks: high temperatures can affect the survival and increase the mortality levels of animal and plant species.
What Causes a Heat Wave to Happen? - Effects of heat waves

Recommendations for heat wave

  • Avoid exposure to the sun: especially at critical hours (from 10 a.m. to 4 p.m.). It is advisable to wear a hat and sunscreen at all times.

  • Drink water more frequently: do so even when you don't feel thirsty.

  • Avoid certain drinks: those with excessive caffeine and sugar can increase dehydration.

  • Fruits and vegetables: incorporate more of these foods into your diet and avoid abundant and heavy meals.

  • Exercise: avoid doing intense physical activity.

  • Clothing: wear loose-fitting and light-colored clothes.

  • Indoors: stay in well-ventilated or air-conditioned places as much as possible (either at home or in public).

  • Warnings: pay attention to warning signs such as intense thirst and dry mouth and skin, temperature above 39 ºC, excessive sweating, feeling of suffocating heat, exhaustion, dizziness or decompensation, stomach aches, lack of appetite, nausea or vomiting, headaches, and many other symptoms.

Learn more about how heat affects different objects, as well as the human body, with our article on the difference between temperature and heat.

You can also learn how to better climate control your home with our video below on plants that absorb heat:

If you want to read similar articles to What Causes a Heat Wave to Happen?, we recommend you visit our Environment (other) category.

  • Ministry of Universal Health and Public Health. (2022) “Program for the prevention and attention to problems derived from extreme temperatures in the Valencian Community. Heat 2022”.

  • The Pan American Health Organization (PAHO). “Heat waves and health”. Retrieved from:

  • Thompson, V., et al. (2022). “The 2021 Western North American heat wave is among the most extreme events ever recorded globally.”

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What Causes a Heat Wave to Happen?
Image: Highs scheduled for Friday, June 17, 2022. Source:
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