As daytime temperatures continue to soar during the Netherlands’ fifth heatwave this year, night-time heat, where temperatures stay above 20 degrees, has lagged behind in public discourse despite its effects on the population.
“Night-time heat is an under-examined aspect of heatwaves,” Lisette Klok, researcher at the Climate Adaptation Services foundation, told broadcaster NOS and NRC.
Especially for vulnerable people – including the elderly and those living in asylum seeker centres and prisons – “night-time temperature is important because your body needs the chance to recover from the heat at night. Poor sleep [due to the heat] makes that more difficult.”
Hot nights, which are defined from 11pm to 7am, affect how well people are able to cope during daytime heat. People tend to sleep worse, making them less functional during the day. In addition, homes build up heat because they can’t cool down during the night, meaning neither do their inhabitants.
Climate atlas
The foundation puts out the Climate Impact Atlas, which maps climate effects – from threats of flooding, waterlogging, drought and heat – throughout the country. Using the Atlas, NRC and regional broadcasters found that on average, there are some six tropical nights per year in the Netherlands, although there are regional differences.
Going neighborhood by neighborhood, the journalists found that in parts of South Limburg, there is an average of 15 “sticky nights” annually.
Maastricht has the most hot nights in the country, while the Randstad also has a higher number. The north of the Netherlands sees less than the national average. Urban areas also take a heat hit, with city centres becoming “heat islands” on hot days. Heat in these areas is even worse at night.
“As a result, homes can be cooled less effectively by ventilation,” said Marjolein van Esch, urban microclimate researcher at TU Delft. “This depends on the difference in air temperature between indoors and outdoors. The greater that difference, the easier it is to cool. Due to the urban heat island effect, that temperature difference is smaller.”
Elderly
The high night-time temperatures have a particularly strong effect on older people, who are more vulnerable to heat.
That led some nursing homes being evacuated earlier this summer, including the De Taling care home in Den Bosch and a facility in Raalte whose systems temporarily failed in July.
“Many buildings are designed for a different climate,” a spokesperson for the care organization Carinova told NOS. “The climate systems were tested to the limit at some locations this summer.”
Temporary portable air conditioners and moving residents to cooler rooms helped ease the problems.
Asylum seekers and prisoners
Since 2021, new homes must meet certain requirements to prevent overheating, but the rules don’t apply to existing houses and also usually not to care homes, prisons and asylum seeker centres. Requirements also vary depending on the region.
But residents of asylum seeker centres and prisons, who have nowhere else to go, are not allowed to install air conditioners on their own. Refugee settlement agency COA allows only one fan per room.
According to NRC, the Dutch Correctional Institutions Agency said increasing temperatures in prisons in recent years mean it needs more resources to cool things down. “Many buildings are due for major maintenance or renovation.”
