Heat stress in the city of Rotterdam (HSRR05)

Heat stress seems to be a serious, but underestimated problem. The heat wave during the summer of 2003 caused 1.400 – 2.200 heat related deaths in the Netherlands. Reducing the Urban Heat Island effect (UHI effect), heat stress and its consequences is a component of adapting to climate changes in Rotterdam.

In this project the UHI effect over Rotterdam was estimated, measured and analysed to determine the magnitude, causes, mechanisms and frequency of occurrence in the present and in the future. As a part of the research, satellite imagery was analysed, various measurement campaigns were carried out, health effects were identified, causes of the UHI effect were determined and an inventory of measures was produced, which were judged on their effectiveness. A workshop with experts and policy makers was organised in order to discuss the preliminary results and to identify recommendations.

It turned out that in summer, an urban heat island effect does occur in Rotterdam. On windless nights, the temperature difference between urban and rural parts may get as high as 8○C.

In the Netherlands, the amount of deceased persons increases with 12% during heat waves. It is, however, difficult to tease out what the consequences are of the heat island effect on the residents of Rotterdam. Nevertheless, an investigation into the quality of sleep among the elderly in the district of Ommoord showed that their sleeping times are shorter and more restless during warm periods. Moreover, it appeared that in the summer of 2006 around 600 heat-related health complaints were registered by general practitioners in the region of Greater Rotterdam (Rijnmond).

Observations indicated that the heat island effect occurs specifically during windless weather conditions. The heating of the air in urban areas under those conditions was mainly determined by the geometry of the built environment (sky view factor) and the albedo and emissivity of the surface materials. Measures such as changing the colour of materials used in facades and paving turned out to be quite effective. Furthermore, both model simulations and field observations confirmed that greening the environment reduces air temperatures. Surface water also may have a cooling effect, but this depends heavily on the temperature difference between water and air. Both water and vegetation have the advantage of providing access to cooling breezes, which help to reduce both the air temperature and the Physiologically Equivalent Temperatures (PET) to a comfortable level. Other promising measures concerned the adaptation of human behaviour.

Eventually, the research projects lead to the following practical recommendations:

    • Start by taking measures indoors aiming at the capacity to recover from heat stress
    • Help people to adjust their behaviour to heat conditions, thus preventing or reducing heat stress (retreat to cool spots, adapt clothing, drink more water, keeping windows closed during the daytime and open at night, etc.)
    • Improving the indoor climate with insulation, ventilation, fixed blinds at the southern facades, etc.
    • Choose from a range of supplementary measures which have a positive effect on the city’s air temperature, don’t have a chilling effect in winter and which can be undone relatively easily, such as: installing fountains and small green areas, greening roofs and facades, apply temporary shading, flush or spray roofs, facades and streets. Use rainwater instead of tap water as much as possible
    • If applicable, carry out additional larger-scale measures such as creating more room for wind, adaptation of lining materials used on roofs, facades and paving or smart design of (new) open water.