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Heat wave

Thermometer indicating a temperature of around 40 degrees
A heat wave is a period of at least five consecutive summer days when the temperature reaches at least 25 degrees, and at least 30 degrees on three of these five days (tropical days).

The impact of a heat wave depends on its duration and temperature. For example, when it does not cool down much during the night, the body has more trouble recovering between hot days. Older people in particular often have a hard time of it.


  • Keep up to date with the weather forecast to know when it will be hot (e.g. via radio, TV, the RMI website or app).
  • Ask your doctor about the risks to your health if you are a high-risk person, e.g. a heart patient, an elderly person, etc.
  • If you are taking medication, check with your doctor or pharmacist to see if it can have a negative impact on your health during a hot spell.
  • If you know people who may need help, stop by to help them prepare.


  • Drink plenty of fluids (1 to 1½ l per day). Do not wait until you are thirsty. Water is better than soft drinks.
  • Are you going somewhere and will you need to spend a long time on the bus, train or in the car? Take a bottle of water with you.
  • Put on a cap or hat.
  • Is it really hot outside? Avoid the sun and stay inside until it is cooler. If that is not possible, stay in the shade as much as possible. Avoid strenuous physical effort or exercise, especially in the heat of the day.
  • Wet your forehead and neck regularly.
  • Wear light clothes in light colours.
  • Protect your skin against the sun: use sunscreen with a high protection factor.
  • If you experience cramps, high fever, headache or faintness, call your doctor.
  • Call 112 immediately if your body temperature is very high (40°).
  • Do not leave people or animals in a parked vehicle.


  • Consult your family doctor if you continue to feel bad.
  • Keep drinking enough.
  • Get enough rest.

Impact and probability

Heat wave. Impact: moderate impact. Probability: very likely.Extreme weather phenomena, such as a heat wave, occur several times a year. It is expected that these risks will become more frequent and greater in the future, under the influence of climate change.

In 2018, the National Crisis Center coordinated a large-scale risk assessment for Belgium for the period 2018-2023. Several experts assessed various risks based on their probability and their impact on people, society, the environment and the economy.

For the risk of 'heat wave', the analysis is:

  • Impact: moderate impact 
  • Probability: very likely

Read more about this analysis and what this chart means.

What do the authorities do?

The various authorities in Belgium have an ozone and heat plan. This plan consists of 3 phases:

  • Vigilance phase: every year from 15 May to 30 September.
  • Warning phase: when the temperature threshold is exceeded.
  • Alert phase: when:
    • The temperature threshold of the warning phase has been reached.
    • The predicted maximum temperature for the day is higher than or equal to 28 °C.
    • A too high ozone concentration has been measured at least one measurement point.
    • Additional measures are needed.

Each regional government adopts measures during a vigilance or warning phase, for example supporting professionals who work with vulnerable groups. When a state of alert is declared, the federal government assumes a coordinating role.