Today marks six years since the national heat record was broken in the Netherlands. In Gilze-Rijen, a temperature of 40.7 degrees Celsius was recorded on July 25, 2019. Extreme heat is an increasing risk for society, with consequences for health, infrastructure, nature, and the economy. Earlier this month, a code orange for heat was issued in parts of the country. According to the KNMI’23 climate scenarios, we will face code orange for heat more often in the future. The duration and maximum temperature change little on average but contain rare outliers far above. The increase in the number of code oranges for heat strongly depends on greenhouse gas emissions.

Code orange for heat

The KNMI issues weather warnings during extreme weather. Since 2015, the warning system for extreme heat has been expanded, and (in addition to code yellow) code orange can also be issued for extreme heat. In 2021, the criteria for this were tightened. The current guideline states that code orange applies if at least one of the following criteria is met: three consecutive days with a maximum temperature of 34°C or higher, two consecutive days with a maximum temperature of 36°C or higher, or one day with a maximum temperature of 38°C or higher. In total, code orange has been issued five times: in 2018, 2019, 2020, 2022, and this year in Noord-Brabant, Limburg, and Gelderland, on July 1 and 2, 2025. 

240 years of daily weather

The KNMI’23 climate scenarios combine two emission scenarios (high or low emissions of greenhouse gases due to human activities) with two climate variants: a wetter and a drier future perspective. For each scenario, a climate model simulated 240 years of daily weather in the Netherlands for the periods around 2050 and 2100. This has also been done for the climate of the recent past (1991-2020). 

Number of code oranges for heat per year

From the time series of daily maximum temperatures in the future, it has been calculated how often the criterion for code orange for heat is met. In the simulated recent climate, code orange occurs in De Bilt on average 0.05 times per year (once every 20 years). Around 2050, the criterion in De Bilt is 0.1 to 0.35 times per year (once every 3 to 10 years), and around 2100 it is 0.1 to 2.2 times per year (over 2 times per year to once every 10 years), depending on the scenario (see image 1).

Code orange for heat occurs most frequently in the scenario with high emissions and strong drying in the summer. Due to the drying, there is less cooling from evaporation, causing heat to occur more often. The number of code oranges for heat is smallest in the scenario with low emissions and slight drying in the summer, but is still twice as large as in the recent climate.