What does the project entail?

In this project we are trying to find the answers to several questions involving nighttime heat:

• How often and where does night heat occur now and in the future?
• What temperatures do residents find unacceptable?
• How high can nighttime temperatures rise now and in the future?
• How long can periods of nighttime heat last, now and in the future?
• What spatial factors affect nighttime heat?
• What urban and residential measures work best to mitigate problems?
• How large can nighttime temperature differences be within built-up areas?

Based on the results of the research, we want to create maps, story maps, graphs and tables that show how often and where average and extreme nighttime heat occurs in Dutch built-up areas. The results will also form the basis for the new climate stress tests for heat and for the development of local heat plans. Furthermore, we will use the insights from the research to improve advice and guidelines on how to design cool outdoor spaces and homes and what else you can do to combat health problems caused by nighttime heat. These guidelines are intended for municipalities, provinces, municipal health services and housing corporations, among others. The guidelines can also be incorporated into national policies and national benchmarks for heat-resistant urban design, cool homes, and heat plans.

What is the aim of the project?

The aim of the project is to provide municipalities, provinces, municipal health services and housing corporations with an understanding of the problems of nighttime heat and to help them come up with good solutions. More specifically, we want to achieve the following:

• The insights help to estimate to what extent and how often nighttime heat may be a problem now and in the future.
• The insights help to estimate where the problem of nighttime heat may be greater. For example, the perceived temperature can be higher in certain areas and air temperatures are often higher in urban areas than outside.
• With the guidelines, municipalities, provinces, municipal health services and housing corporations can take more informed decisions on measures to mitigate problems of nighttime heat.
• The guidelines help evaluate the effectiveness of measures in outdoor spaces. For example, how strong are the cooling effects of green spaces with trees in a street? And do green spaces with trees also reduce heat problems at night?
• The guidelines help evaluate the effectiveness of measures in or around homes. For example, how much can homes cool down if you open your windows opposite each other late at night and early in the morning?
• The guidelines help point residents to what they themselves can do to combat problems caused by nighttime heat.

What is our role?

The project comprises four substantive work packages:

• Development of temperature indicators that describe nighttime heat problems.
• Determination of frequency of occurrence of night heat and recurrence times for current and future climate.
• Description of spatial variation in nighttime heat at three scales: rural, inner-city and within a district.
• Application of knowledge about frequency and spatial variation in nighttime heat to effective cooling solutions.
• Dissemination and interaction with the work field.

We have a role in work packages 1, 2 and 5. We are leader of work package 1. This work package focuses on the following questions: What is a good temperature indicator to identify problems caused by night heat? What indoor and outdoor temperatures do citizens find acceptable? Within work package 2 we investigate which exceptionally hot nights should be taken into account, now and in the future. And within work package 5 we coordinate with the work field which insights are needed to arrive at good temperature indicators and useful advice and guidelines. In this last work package we will develop maps and map narratives for the Climate Impact Atlas and the Climate Adaptation Knowledge Portal. There is already a map narrative on nighttime heat in the Climate Impact Atlas. This map narrative will be updated with the results from this project.

Arthur Maas did research on heat indicators

Arthur Maas worked on the project during his internship at CAS. He conducted an initial exploration into which heat indicators can best describe the problems of night-time heat for the Netherlands. Among other things, his research showed that indicators that indicate perceived temperature, such as PET, are currently still unsuitable for analysing nighttime heat for outdoor temperatures, for example, because they rely heavily on radiation. Arthur therefore recommended adapting the indicators for perceived temperature or developing new ones. He also recommended using indoor temperatures as indicators to describe nighttime heat problems.