Heatwaves in Greece: from 1987 to today, in data

01What counts as a heatwave

The World Meteorological Organization stresses that a heatwave is not just a run of hot days. Its defining feature is heat that builds up over successive days and nights. There is no single global temperature threshold: each country sets its own, based on the local climate.

To compare years, Copernicus uses a simple, fixed rule: a heatwave is at least three consecutive days with a maximum temperature above the 98th percentile of 1961–1990 and above 28°C. You will see it in the figures below.

02The 1987 heatwave: what the mortality data showed

In July 1987 a major heatwave hit Greece. A study from the University of Athens Medical School, led by K. Katsouyanni, was published in 1993 in the Archives of Environmental Health. The researchers compared deaths in July 1987 with deaths in July of the six previous years:

The study also analysed five years of daily data. It found that deaths in Athens rose by more than 40 a day when the 24-hour mean temperature exceeded 30°C. It also found a statistically significant interaction between high temperature and high sulphur dioxide levels: heat was more dangerous when the air was dirtier.

The gap between Athens and the rest of the country is the most telling finding. The same heatwave hit the city far harder.

03Greece heatwaves: the record summers

Analyses by meteo.gr at the National Observatory of Athens and by Copernicus give this timeline:

Heat is not spread evenly. In summer 2024, according to meteo.gr, western and northern Greece were 2–3°C above the 1991–2020 average, locally up to 4°C, while the rest of the country was 1–2°C above. The Aegean had the smallest anomalies, thanks to the meltemi winds, yet nowhere was the anomaly below +1.4°C.

In the same 2026 analysis, meteo.gr estimates that mean summer temperature in Greece rose by 2.5°C from 1960 to 2025.

04Heatwaves and climate change: what attribution says

Attribution studies ask how different an event would have been in a cooler climate. In June 2026 a heatwave hit western Europe, with temperatures up to 12°C above normal in France, Germany, Italy, Spain and southern England. As meteo.gr summarises, an analysis by World Weather Attribution estimated that a similar heatwave would have been about 3.5°C cooler by day in 1976 and about 2°C cooler in 2003. The same article describes heatwaves as Europe's deadliest natural hazard.

05Why Athens does not cool down at night

The WMO explains that cool nights let people and buildings shed the day's heat. When nights stay unusually warm, that recovery is disrupted, and city dwellers are more exposed because of the urban heat island. The 23 tropical nights of 2024 in southeastern Europe, almost three times the average of 8, show why this matters.

We explain how Athens heats up more than its surroundings in our article on the Athens urban heat island, and how risk could be mapped street by street on our urban heat page.

06Heat stroke: symptoms and official advice

This is not medical advice. It summarises the official guidance of EODY, Greece's National Public Health Organization.

Heat stroke

EODY lists high body temperature, irritated, red, dry or moist skin, a fast and strong pulse, headache, dizziness, nausea, confusion and fainting. Its advice: call an ambulance, move the person somewhere cooler and bring their temperature down with cool clothing or a cool bath. Do not give them anything to drink. The emergency number is 112.

Heat exhaustion

Symptoms: heavy sweating, cold, pale and clammy skin, a fast and weak pulse, nausea or vomiting, muscle cramps, tiredness, dizziness, headache, fainting. EODY recommends a cool place, loose clothing, cool wet cloths or a bath, and sips of water. Get medical help at once if there is vomiting, if symptoms get worse or if they last more than an hour.

Who is most at risk

The Civil Protection guidance singles out babies and children, older people, and people with chronic illness or on medication. A cardiologist's article on meteo.gr adds that some heart medicines affect how the body copes with heat, and that you should not stop them on your own but talk to your doctor.

07When is the next heatwave? Where to find warnings

Kassandra Labs does not issue weather forecasts. For official warnings:

• EMY: the Hellenic National Meteorological Service issues emergency bulletins. In June 2024, for example, its director announced an emergency bulletin because temperatures would reach orange on the Meteoalarm colour code.
• Meteoalarm: the European system brings together warnings from 38 national meteorological and hydrological services on one map.
• Civil Protection: heatwave guidance, and 112 for emergencies. For health information, EODY runs a phone line on 1135.

08Frequently asked questions

09Sources

1. World Meteorological Organization — Extreme heat
2. Copernicus — ESOTC 2024: Heat and drought in southeastern Europe
3. Katsouyanni K. et al., "Evidence for interaction between air pollution and high temperature in the causation of excess mortality", Arch Environ Health 48(4):235–42, 1993 (via PubMed)
4. meteo.gr / National Observatory of Athens — Summer 2024: the warmest on record for Greece (6 Sep 2024)
5. meteo.gr / National Observatory of Athens — Summer 2026: the 6th warmest since 1960 (7 Sep 2026)
6. meteo.gr / National Observatory of Athens — Western Europe heatwave and attribution (26 Jun 2026)
7. National Public Health Organization (EODY) — Heat stroke and heat exhaustion
8. General Secretariat for Civil Protection — Heatwave guidance
9. meteo.gr — Heatwave and cardiovascular problems (C. Maniotis, cardiologist)
10. Naftemporiki, 10 Jun 2024 — EMY emergency bulletin for the heatwave
11. MeteoAlarm — European weather warnings