The Netherlands Could Get Its First National Super Heatwave
Forecasters say the Netherlands could record its first national super heatwave this week, with code orange warnings, highs in the mid-30s and three days possibly above 35°C.
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The Netherlands is bracing for a spell of extreme heat this week, with temperatures climbing into the mid-30s and forecasters raising the possibility of a national record. The newspaper AD reported that there is a strong chance the country could see its first national “superhittegolf,” or super heatwave, with three days above 35°C.
What a super heatwave is
The term superhittegolf is not an official one. It was introduced by the weather service Weeronline in 2018 to describe an unusually extreme heatwave. To qualify, the maximum temperature has to reach 30°C or more on five days in a row, and on three of those days it has to climb to at least 35°C, what forecasters call a “zeer hete dag” (very hot day). A regular heatwave, the official measure, is lower: five consecutive days of at least 25°C at the De Bilt weather station, the national reference point, of which at least three reach 30°C.
A national super heatwave has never been recorded at De Bilt, although regional ones have happened, for example in the Limburg village of Arcen in 2003 and 2018, in Volkel in 2015, and at several stations in 2019 and 2020. Weeronline, which coined the term, is more measured about the national picture this week, but says several stations, especially in the southeast, could meet the conditions on Saturday. Like an ordinary heatwave, a super heatwave can only be confirmed after the fact.
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How hot, and when
The KNMI, the national weather institute, has issued code oranje, its second-highest warning level, for extreme heat in the middle and south of the country from Wednesday 24 June until at least Friday 26 June. In those areas, highs of 33 to 36°C are expected from Wednesday, and Friday could be the hottest day; KNMI forecasts up to 38°C, while Weeronline points to 37 to 39°C inland. In the northern provinces of Groningen, Friesland and Drenthe, the milder code geel (yellow) applies, with afternoon temperatures of 28 to 33°C.
The nights will offer little relief. In the larger cities, temperatures are expected to stay between 22 and 27°C overnight, the kind of warm, sticky conditions that make it hard for the body to recover. The KNMI’s new heat-stress index, called hittekracht, which combines temperature, humidity, wind and sunshine on a scale from 0 to 10, is forecast to reach 9 to 10 in the middle and south.
A possible record-long June heatwave
Beyond the heat itself, forecasters are watching the calendar. Weeronline expects the official national heatwave to begin on Wednesday or Thursday and to last at least into the weekend. If the warmth continues into the following week, the company says, it could become the longest June heatwave on record. The current record for the month is eight heatwave days, set in June 1976 and June 1936.
Health risks and the National Heat Plan
The National Heat Plan, a warning system run by the public health institute RIVM, is in force. It is meant to prompt extra attention for people who are more at risk in the heat, especially those over 75, people with chronic illnesses, socially isolated people and young children, whose bodies regulate temperature less well.
The advice is practical. People are urged to check on vulnerable neighbours and relatives, to drink more than usual even without feeling thirsty, to keep homes cool by closing curtains and windows during the day, and to avoid heavy physical activity between noon and 6 pm. Forecasters also warn of very strong sun, with a UV strength high enough to cause sunburn within 10 to 15 minutes around the middle of the day.
The bigger picture
The KNMI places the heat in the context of a changing climate. According to the institute, the chance of the temperatures expected this week is now about three times greater than it was a little over a century ago, and the current heat has become roughly 2.5°C warmer since measurements began in 1901. The highest temperature ever recorded in the Netherlands remains 40.7°C, measured on 25 July 2019 in Gilze-Rijen.