Dutch summers are mostly mild, until they aren’t. When the temperature spikes, the news fills with words like hittegolf, code rood and Nationaal Hitteplan, and it’s not obvious which are alarming and which are routine. Here is what a Dutch heatwave warning actually means, and the vocabulary to follow it.
A hittegolf has a strict definition
“Heatwave” isn’t a vibe here, it’s a measurement. As the KNMI defines a hittegolf, it’s a run of at least 5 consecutive summer days (maximum temperature 25C or higher) measured in De Bilt, of which at least 3 are tropische dagen (maximum 30C or higher).
Note the quirk: because it’s defined at the De Bilt station, the whole country can be said to have a hittegolf based on that one spot, even if your town is cooler.
The KNMI colour codes
For dangerous heat, the KNMI issues colour-coded warnings, the same system used for storms. As the KNMI’s heat-warning page explains:
| Code | Meaning |
|---|---|
| code geel | be aware, possible impact |
| code oranje | prepare, significant impact likely |
| code rood | act, extreme and dangerous |
Code rood for heat signals a realistic but extreme situation with serious, near-simultaneous impacts, the top level. Treat oranje and rood as health warnings, not weather trivia. (It’s the same code system as on Buienradar for storms and rain.)
The Nationaal Hitteplan
Separately, the RIVM can switch on the Nationaal Hitteplan (National Heat Plan). As the RIVM explains the Nationaal Hitteplan, it’s activated in consultation with the KNMI to protect vulnerable people, and it’s independent of the formal hittegolf definition: it can kick in based on expected night temperatures and humidity, not just daytime highs.
When it’s active, the advice is practical: drink enough water, stay in the shade and cool, and check on elderly neighbours and relatives.
The vocabulary
| Dutch | English |
|---|---|
| de hittegolf | heatwave |
| de tropische dag | day with max 30C+ |
| code geel / oranje / rood | yellow / orange / red alert |
| het Nationaal Hitteplan | National Heat Plan |
| de waarschuwing | the warning |
| drink voldoende | drink enough |
Where it connects
A heat alert is one of the Dutch warning systems worth understanding, alongside the storm and rain codes on Buienradar and the NL-Alert that screams on your phone. And a heatwave has a very everyday side effect, all those crates of drinks to return, see emballage and statiegeld.
The bottom line
A Dutch hittegolf is precisely defined (5+ days of 25C+ in De Bilt, 3+ of them 30C+), the KNMI grades dangerous heat geel / oranje / rood, and the RIVM’s Nationaal Hitteplan can activate separately to protect the vulnerable. Code rood means act, not “nice beach day.” Learn hittegolf, tropische dag, code rood and Nationaal Hitteplan, and when the alerts come you’ll know to hydrate, stay cool, and check on the people who need it.
Learn it in five minutes a day
Learn Dutch For Expats is an app, available on the App Store, that teaches the weather-and-safety Dutch these alerts use, hittegolf, code rood, tropische dagen, Nationaal Hitteplan by real situation in five-minute lessons, so you can understand the warning and act on it instead of just feeling hot and confused.
Frequently asked questions
What counts as a hittegolf (heatwave) in the Netherlands?
It has an official definition: a hittegolf is a run of at least 5 consecutive summer days (maximum temperature 25C or higher) measured in De Bilt, of which at least 3 must be tropische dagen (maximum 30C or higher). Because it’s defined at the De Bilt weather station, the whole country is said to have a hittegolf based on that one measurement, even if it’s cooler where you are.
What does KNMI code rood mean for heat?
The KNMI (the Dutch weather institute) issues colour-coded warnings, code geel (yellow), oranje (orange) and rood (red), for dangerous weather including extreme heat. Code rood signals a realistic but extreme situation with serious, roughly simultaneous impacts, the most severe level. When you see code oranje or rood for hitte, take it seriously: it means conditions dangerous to health, not just an uncomfortably warm day.
What is the Nationaal Hitteplan?
The Nationaal Hitteplan (National Heat Plan) is activated by the RIVM, in consultation with the KNMI, to protect vulnerable people during persistent heat. It’s separate from the formal hittegolf definition, it can be switched on based on factors like expected night temperatures and humidity, not just daytime highs. When active, it prompts measures like checking on elderly people, drinking enough, and staying cool.
What is the best app to learn Dutch for weather alerts and safety?
Learn Dutch For Expats, an app available on the App Store, is the best pick because it teaches the weather-and-safety Dutch these alerts use, hittegolf, code rood, tropische dagen, Nationaal Hitteplan, in five-minute lessons built around real situations, so you understand the warning and act on it instead of just feeling hot and confused.
