Cold wave/frost
In the Netherlands, the Royal Netherlands Meteorological Institute (KNMI) defines a cold wave as a period of unusually cold weather with maximum temperatures below 0.0 °C (ice day) for at least five consecutive days. At least three of these days must have severe frost, with minimum temperatures below -10.0 °C. This definition is based on the measurements from the weather station in De Bilt, where the KNMI is located.
Cold waves are quite rare in the Netherlands. Since 1900, there have been 33 cold waves. The most recent cold wave took place in 2012. That winter the temperature dropped to -18.9 °C. One cause of cold waves are atmospheric blockades. This happens when a stable high-pressure area disrupts the normal movement of air in the atmosphere. In winter, these blockades can hold cold air from Scandinavia or Siberia and cause a cold wave in the Netherlands.
Difference between frost and ice day
An ice day is a day when the temperature remains below 0.0 °C throughout the entire day. This means the maximum temperature is below the freezing point. During the period 1991-2020, the average number of ice days ranged from about 2 in the southwest of the Netherlands to around 10 in the northeast.
A frost day is a day where the minimum temperature drops below 0.0 °C. The maximum temperature is not considered. Frost is measured on a height of 1.5 meters above the ground. Frost days usually happen between October and April. During the period 1991-2020, the average number of frost days ranged from about 20 in the southwest of the Netherlands to around 65 in the northeast.
In the Netherlands, different categories of frost are distinguished:
- Light frost: temperatures between 0 and -5.0 °C.
- Moderate frost: temperatures between -5.0 and -10.0 °C.
- Severe frost: tempertures between -10.0 and -15.0 °C.
- Very severe frost: temperatures below -15.0 °C.
Impact of cold waves
During cold waves, there is a higher risk of mortality in nature. As cold waves become less frequent due to climate change, the survival chances of some insects, parasites, plant disease and invasive species are expected to increase. This may contribute to a rise in allergies, infectious diseases and pressure on agriculture and biodiversity. Cold waves can also lead to disruptions in heating, water and electricity supply (PDF) as well as problems affecting infrastructure and transport. Particularly elderly people and those with existing health conditions are the most vulnerable to cold waves.
