Evaluating the effectiveness of the Dutch National Heatwave Plan

In the Netherlands, the average annual temperature has increased by more than 2.5 °C since 1901 (KNMI, 2026). Since 1991, the observed rate of warming - 0.4°C every ten years - is twice as fast as the global average rate of warming. Moreover this rate roughly corresponds to the rate of warming between 1991-2020 and 2050 which is projected in the Royal Netherlands Meteorological Institute (KNMI) 2023 climate scenarios under the high greenhouse gas emissions scenario (KNMI, 2025).

The Netherlands now has more days with temperatures of at least 25 °C and summers have more tropical nights, with a minimum temperature of 20°C or higher. Heatwaves are increasing in number, duration and intensity, and extreme temperatures are being reached, with a maximum of 40.7 °C in 2019.

According to KNMI’s high greenhouse gas emissions scenario (H), the number of tropical nights each summer (minimum temperature > 20°C) will increase from 0.3 nights in the current climate to 3 nights around 2050 and up to 19 nights in 2100 in De Bilt. In the low greenhouse gas emissions scenario (L), there will be about one tropical night per summer from 2050 with temperatures stabilising after 2050. In the H-scenario, the number of summer days (≥ 25°C) per year in De Bilt will increase from 28 days in the current climate to 49 days around 2050, and up to 89 days around 2100. In the L-scenario, there will be 40 summer days per year from 2050.

Heat is one of the most serious and urgent climate-related risks for human health. Exposure to high temperatures places strain on the body's thermoregulatory processes and can result in many health complications, see Heat | Health impacts | European Climate and Health Observatory Climate-ADAPT. When heat stress is severe, it can lead to hospitalisation and death. A previous study showed that approximately 660 people die each year in the Netherlands due to high temperatures. Older adults, in particular those above 75 years of age, have a higher risk of dying on days with high temperatures (RIVM, 2024). Older adults, in particular those above 75 years of age, have a higher risk of dying on days with high temperatures. Furthermore, the Dutch population is aging, which means the number of people vulnerable to heat is expected to increase. Therefore, measures to reduce heat-related health impacts are essential. However, there is a general lack of public information about the effectiveness of HHAPs, which poses a challenge to understanding the effectiveness of  implemented measures in reducing heat-related health impacts (EEA, 2024). Regular evaluations of HHAPs can thus help to identify the measures and strategies that most effectively contribute to the reduction of heat-related health impacts. However, comprehensive evaluations of the effectiveness of HHAPs are rare and challenging, as well as being costly.

The Dutch Heatwave Plan (HP) is a warning system and communication plan aimed at ensuring that information reaches at-risk groups and those in their immediate environment in a timely and complete manner. This includes, among others, the institutions with which at-risk groups are in contact, as well as other healthcare providers and volunteers who are part of their support network. Ensuring awareness and knowledge of the health impacts of heat are necessary for appropriate action to be taken during a period of sustained heat.

The Dutch HP was established in 2007 as a collaboration between the Ministry of Health, Welfare and Sport, RIVM, KNMI, the Dutch Red Cross, the Association of Municipal Public Health Services and Medical Assistance in Accidents and Disasters (GGD GHOR NL) and several healthcare sector organisations. The HP is designed to provide timely alerts when prolonged warm weather is forecast, so that measures can be taken to reduce and, where possible, prevent health complaints due to sustained exposure to heat. RIVM is responsible for activating the HP, for alerting organisations and for issuing communications. The plan was first activated in 2010.

A comprehensive evaluation of the HP was carried out by RIVM, with the aim of identifying improvements that would protect the health of people in the Netherlands from heat even more effectively. The evaluation consisted of four studies, each of which was designed to assess the effectiveness of different components of the HP.  

1. An epidemiological analysis of changes in heat-related mortality before and after the first activation of the HP 
2. An evaluation of the communication message 
3. An evaluation of the implementation of the behavioural recommendations in practice 
4. A scenario exercise assessing preparedness for extreme heat events 

The purpose of the evaluation of the HP was to identify improvements to protect health and lives of people in the Netherlands from heat. The evaluation consisted of four components, each of which was designed to assess the effectiveness of different aspects of the HP. Subsequently, recommendations from the evaluation will be implemented to strengthen actions taken under the HP.

1. Epidemiological analysis of heat-related mortality

The goal of this study was to evaluate the effect of the HP on the relationship between high temperatures and mortality in the Netherlands. RIVM analysed the temperature-mortality associations and estimated the number of temperature-related deaths during the warm season (May–September) in the Netherlands, in the years before (2000–2009) and after (2010–2019) the first activation of the HP. RIVM analysed whether associations differed by age, sex, neighbour­hood socioeconomic status (SES), and degree of urbanization.

The analysis showed an increased mortality risk (the probability of dying in a defined population within a defined time period) at high temperatures. The mortality risks at high temperatures in 2010–2019 were lower than in 2000–2009, especially among the elderly, women, and residents of neighbourhoods with low SES. The estimated number of deaths related to potential days that the HP would have been activated was around 4,200 in 2000–2009 and around 2,400 in 2010–2019. Among those aged 90 and older, the mortality risk at high temperatures strongly decreased, but the number of heat-related deaths in 2010–2019 changed only slightly compared to 2000–2009. This is because the population aged 90 and older increased in 2010–2019. When heat-related mortality is expressed as a percentage of total mortality in the 90+ population, it decreased from 2.0 percent in 2000–2009 to 1.3 percent in 2010–2019.

The HP may be one of the factors that contributed to the weaker associations between high temperatures and mortality in 2010–2019 compared with 2000–2009. The strongest attenuations in risk were found for the elderly, a group that is specifically tar­geted by the HP. Strong attenuations in risks were also observed for women and for low-SES groups. The HP does not specifically focus on these groups, but they may be more aware of HP activations or follow precautionary measures better than other groups.

The decrease in mortality risks at high temperatures over time can be explained by multiple factors. The publication and first activation of the HP may have played a role in reducing mortality risks, but other factors could also have influenced this. Analyses by 5-year periods show that lower mortality risks at high temperatures were already observed in 2007–2011, partly before the first activation of the HP. This could be due to the heatwaves in 2003 and 2006, which were the longest and most intense in the Netherlands and attracted much (media) attention. This may have increased awareness among people and institutions about the risks of heat before the publication and first activation of the HP.

Nevertheless, although the associations between high temperature and mortality have decreased, high temperatures still remain associated with increased mortality risks. As the proportion of elderly people and the number of warm and hot days are projected to increase in the future in the Netherlands, the mortality attributable fraction of high tem­perature may increase in the future. Therefore, a continued focus on measures to reduce heat-related mortality and disease burden remains necessary.

2. Evaluation of the communication message of the HP

The goal of this study was to evaluate the effectiveness of the HP’s communication message. RIVM investigated how the current message is received and understood by the general public and to what extent it motivates them to protect themselves and/or vulnerable people in their environment from heat. Additionally, RIVM developed and tested an alternative version of the infographic about the HP, with the core message ‘look after each other’, aimed at everyone who might provide care to at-risk people, such as the elderly, sick, and those in need of assistance.

A survey was held amongst a representative sample of the Dutch population to study the following questions:

• How do people experience heat, and what do they know and think about the HP and its communication message?
• To what extent do people expect to adjust their behaviour when the HP is activated to protect themselves and/or a vulnerable person in their environment from heat?
• To what extent are there differences in these outcomes between the current and alternative versions of the RIVM infographic?

The results found that most people have a positive attitude towards the public information provided by the HP about heat. The communication message appears to contribute to awareness of the possible health impacts of a heatwave, especially for vulnerable people. The behavioural advice is well remembered and is seen as useful and feasible. When the HP is activated, most people, including a large majority of vulnerable people, expect to adjust their behaviour to protect themselves from heat. In addition, about half of the population expects to pay extra attention to protecting vulnerable people in their environment from heat, such as the sick, those in need of care, and young children.

The alternative version of the RIVM infographic seemed to make people understand better what was expected of them. Notably, this version motivated more people - especially those who do not regularly care for others - to be extra attentive to vulnerable people around them during heatwaves. This highlights the importance of placing the core message ‘look after each other’ more prominently in communications around heat.

Based on the results of this study, the earlier version of the infographic was replaced by the version developed and tested in this study and has been in official use since 2025. This version provides concrete advice on monitoring health signals and heat-protective behaviour by caregivers that are easy to carry out. More diversity has also been introduced in the images of care recipients and caregivers, so that as many people as possible feel addressed by the information.

For extreme heat conditions, such as an expected upcoming heatwave with temperatures around 40°C (red heat health warning scenario) or during a large outdoor event, different types of communication are needed. In such circumstances, everyone is vulnerable to the effects of heat. This study recommended developing and testing specific communication materials for these situations as well. In these messages, alongside ‘look after each other’, the core message ‘look after yourself’ should also be included. As a result, infographics for an orange and red heat health warning scenario were developed by RIVM in Spring 2026.

3. Evaluation of the implementation of the behavioural recommendations in practice

RIVM investigated to what extent the current heat warning message reached its intended target groups - vulnerable people and the people who care for them -, and to what extent these groups carried out the recommended actions and the factors which influence this.

Shortly after the activation of the HP in June 2025, a survey was conducted among people aged 65 and older (n = 804), informal caregivers (n = 586), and healthcare professionals (n = 405). Additionally, in-depth interviews were held with healthcare professionals (n = 31) to gain further insight into the application of heat protocols in community nursing and residential care for the elderly.

Survey findings:

• The survey found that nine out of ten people recorded seeing heat-related behavioural advice during the hot days of summer 2025.

• Fewer than half of those in the surveyed groups acted on the following: checking or adjusting medication (this was not considered part of the care service provided) and offering a foot bath (this was seen as unnecessary or too time-consuming)

• Over six in ten people aged 65+ believed they could recognize health complaints caused by heat; among informal caregivers and healthcare workers, five and six in ten, respectively, believed they could recognize these complaints in those they cared for.

• One in five people aged 65+ had difficulty keeping their home cool and two in five caregivers could not easily keep their clients’ homes cool.

• One in three of those aged 65+ felt the behavioural advice did not apply to them. This was more common among 65-74 year-olds than those 75 and older. Two-thirds aged 65+ estimated the chance and severity of heat-related health complaints as low.

• Notably, most behavioural advice was seen by a majority of respondents as meaningful and easy to carry out. The more meaningful and easy to carry out an advice seemed, the more likely people were to follow it.

• Concerning informal caregivers, most said they had not received advice specifically relevant to their caregiving tasks and half of them experienced a higher caregiving burden during heat.

• Concerning healthcare professionals, some of those interviewed indicated that they found the HP patronising or unnecessary. Healthcare workers have internal heat protocols at work and much knowledge through their training. They also indicated that regarding outpatient care, homes that are too warm affect both patients and staff. Furthermore, climate control of buildings is an important issue in institutional care.

Based on the results, the following recommendations were formulated to improve the reach and implementation of behavioural advice:

• Emphasise the reasons for and ways of following the advice that is relatively less well followed, for example, checking medication and monitoring health. The RIVM infographic contains this concrete advice.

• Address informal caregivers more directly, for example through communication via patient or interest groups. Mention that informal caregivers may also face a heavier burden during periods of heat, and some also belong to the vulnerable 65+ group. An additional advice could be to enlist extra help and share tasks.

• Invest in climate adaptation for buildings where vulnerable people live or stay. This is important not only for residents but also for their (informal) caregivers who experience higher work pressure during heat. Some subgroups may be less well reached (e.g. people with low literacy) or have fewer opportunities to keep their homes cool (e.g. in poorly insulated homes). Consider follow-up research on these groups and on how well citizens and (informal) caregivers are prepared for a red extreme heat warning scenario.

4. A scenario exercise assessing preparedness for extreme heat events

In order to test the extent to which Dutch people are prepared for extreme heat, RIVM drew up a extreme heat scenario. This scenario of a red extreme heat warning describes a realistic, extreme heat situation with various effects occurring almost simultaneously. RIVM discussed this scenario with various heat experts and stakeholders in a workshop attended by national, regional and local organisations. 

Workshop participants discussed whether the Netherlands is sufficiently prepared for a red extreme heat warning. Other topics addressed were the intended goals of a red extreme heat warning, the roles and tasks of organisations, and whether national and regional heatwave plans can play a complementary role in the preparations for extreme heat.

The scenario analysis revealed a number of considerations in order to be better prepared for extreme heat. For example, it is difficult to determine exactly when extreme heat is actually disruptive to society as heat has (cascading) effects on many sectors, such as infrastructure, health care, energy, agriculture, etc. Moreover, no organisation has oversight of all the impacts and there is not always communication between the sectors. There is also no agreement between local, regional, and national parties on the goals to prepare the Netherlands (including the overseas territories in the Caribbean) for extreme heat. 

The analysis also showed that standard crisis response solutions may not be sufficient in the event of extreme heat. For example, a sports hall might be used as shelter in the case of evacuation due to e.g. wildfires, but this same shelter might not be suitable in hot conditions. There are also different expectations of roles, tasks and responsibilities of various parties, such as municipalities, safety regions (public bodies who facilitate regional cooperation in dealing with crises and disasters) and ministries.

Based on these considerations, RIVM formulated a number of recommendations to ensure that the Netherlands is better prepared for extreme heat.

• Reach consensus between local, regional, and national parties on the goals to be pursued during extreme heat.

• Let the regions and the overseas territories in the Caribbean specify which problems arise during extreme heat and what kind of national support is needed, using the system of regional risk profiles. Then assess how these needs can be met through national policy.

• Invest in individual and community resilience to increase society’s overall resilience.

• Let central government work with the regions and Municipal Public Health Services (GGDs) to make plans on how to deal with extreme heat by incorporating heat into existing national and regional crisis plans. Agree on what to do if emergency service capacity proves insufficient.

• Ensure that one government department takes responsibility for preparedness and response to heat.

• Provide clear communication messages tailored to each relevant target group about the dangers of heat, including advice on actions to take, possibly also during the colder phase, to enhance individual and community resilience and foster a cultural change.

• Consider who should deliver the communication message and whether communication should be escalated to national level during extreme heat, with a clear national red extreme heat warning message.

• Have the Weather Impact Team (WIT) develop measurable guidelines for when a red extreme heat warning should be declared, based on recent experiences with extreme heat and guidance from other countries. Also, consider what expertise the WIT should have to make an integrated assessment of the expected heat impact.

• Better prepare buildings and other locations for heat by adapting building plans and spatial planning.

Once the evaluations were completed, the next steps were to implement the recommendations. Based on the evaluation of the communication message of the HP, the previous version of the infographic was replaced in summer 2025 by the version developed and tested in the evaluation. Prior to the evaluation, the HP was activated in a binary fashion, with no further escalations: it was either active or not. The evaluation recommended developing and testing specific communication materials for more extreme heat conditions. Therefore, infographics for an orange and red heat health warning scenario were developed by RIVM to be ready for use in summer 2026. Having advice ready for possible yellow, orange and red heat health warnings also means that the HP is better aligned with KNMI’s weather warning system.

The trigger for activation of the HP is now predominantly meteorologically driven, although health impacts are taken into account when deciding whether to activate or not. Plans are under way to change this to impact driven, using mortality risks as a possible trigger.

At the start of the project, stakeholders were interviewed to inform the evaluation.  

The general public was surveyed to evaluate the communication message of the HP, and healthcare professionals and informal caregivers were surveyed during the evaluation of the implementation of the behavioural recommendations, see above. In-depth interviews were also held with healthcare professionals. The surveys and interviews provided interesting insights. For example, one in three of those surveyed aged 65+ feel that the behavioural advice does not apply to them, although they are the target group. And some healthcare professionals when interviewed said that they find the HP patronizing or unnecessary. 

During the evaluation, stakeholders were also involved in the scenario exercise which assessed preparedness for extreme heat events. These included the Ministry of Health, KNMI, Red Cross and umbrella organisations in the healthcare sector.

Success factors of the evaluation:  

• Sufficient funding from the Ministry of Health 

• Availability of mortality and meteorological data 

• Interdisciplinary collaboration between colleagues at RIVM 

• Sense of urgency generated by the media and politicians 

• The evaluation was very comprehensive and gave valuable insights into both the process and the outcomes of (activation of) the HP. 

• The four parts of the evaluation led to recommendations for both policy and practice. 

• The insight that mortality has decreased in the period after the first activation of the HP, compared to the period before. This implies that adaptation measures in the Netherlands have worked and that people have become more aware of the effects of heat on health. Moreover, the reduction was greatest in vulnerable groups, such as the elderly and people living in low-SES neighbourhoods. 

Limitations of the evaluation:

• The epidemiological study only focused on mortality, which is the tip of the iceberg concerning the health effects of heat. In future studies we would like to look at the effects of the HP on indicators of morbidity, such as hospitalisations or emergency department visits.

The total evaluation costs were > 500K euros. A cost-benefit analysis was not considered. However, the costs of the evaluation are negligible compared to the benefits of the HP in terms of keeping people healthy during heat.

Some of the recommendations have already been implemented and others are ongoing, see 5.5 Solutions. It is expected that most of the recommendations from this evaluation (for which there is funding to implement them) will be implemented in 2026.  

As evaluation is cyclical, this process will continue into the future.  

RIVM employees: Werner Hagens, Jochem Klompmaker, Liesbeth Claassen, Rosanne Fikke, Anne Buitenhuis, Floor Kroeze, Sylvia Versluis, Colene Zomer, Lisbeth Hall

Contact: cGM@rivm.nl

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