Heat-resistant Netherlands: this is how we can cope with the increasing heat

The Heat Power Index, developed by TNO, KNMI, RIVM and the Free University, offers a new perspective on how we deal with heat. This index looks beyond temperature and also considers humidity, radiant heat and wind. This allows us to better prepare for extreme heat, similar to how we understand wind force. The model takes into account how heat fit a person is, depending on health, clothing and activity, which is crucial for assessing risk in different populations. The heat strength index is a response to the increasing heat caused by climate change and helps take appropriate action on hot days. With this scale, the elderly as well as festival-goers and outdoor workers can make more informed decisions about their activities during hot days. The impact of heat thus becomes clearer, as does the need for adaptation measures.

Concrete impacts of heat stress

The 2024 Dam to Dam Run demonstrates the need for a better heat index. Seemingly mild temperatures of 23 degrees Celsius caused serious health problems. The combination of factors such as solar radiation, restricted winds and increased humidity made the situation dangerous, leading to the event being halted for the last group of participants. This incident highlights that the traditional focus on temperature alone is insufficient. Boris Kingma (TNO): “Very often we don't actually look at anything but temperature, but we know that other factors also matter a lot for the effect of heat on humans.”

Image: TNO

Scientific Basis

The new WARM model relies on the 'wet-bulb globe temperature' (WBGT), recognized as the most reliable indicator of heat stress. Rob Sluijter of KNMI points out an important problem: “The WBGT, like ordinary air temperature, is expressed in degrees Celsius, which has a misleading effect.” The WBGT has increased by an average of 2 points over the past few decades, leading to a more than doubling of the number of hours when sporting events cannot safely take place. This increase demonstrates the urgency of a new, understandable warning system.

Heat Fit: Personal Resilience

The innovative aspect of the model is the introduction of the concept of “heat fit. This takes into account individual factors such as health, clothing choice and environment. The impact of heat varies significantly by occupational group and activity. Police officers and ME officers in uniform, construction workers working outdoors, and festival goers each have their own risk profile. Werner Hagens of the RIVM signals da tthe current approach can be perceived as patronizing: “What we often hear now at the RIVM is that it can be patronizing when we say: ‘drink enough, take it easy, keep your house cool’.”

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Practical implementation

Like wind force, the heat stress index is expressed in a numbered scale starting at 1. KNMI is preparing to integrate this index into their weather warnings. The scale will be displayed in the recognizable colors red, orange, yellow and green. This should lead to an intuitive system that helps people make daily decisions.

Future outlook

The coming year will be crucial for the further development of the heat force index. KNMI will first practice with the system before it is widely implemented. The initiators are calling on stakeholders to work together to further concretize the concept of heat force and heat fit. Rob Sluijter suggests that behavioral scientists may be able to play an important role: “Calculating the WBGT and devising the model, the five of us here will do that.” This multidisciplinary approach should ensure an effective system to help the Netherlands adapt to the increasing heat caused by climate change.