Evaluation of the health-risk reduction potential of countermeasures to urban heat islands

• A heat-health risk concept, which includes indoor hazards, is applied successfully.
• Heat-related deaths (65+) double with an increase of 1 K in mean ambient temperature.
• Most countermeasures to UHI only have a low impact on indoor hazards and risk.
• Trees, cool roofs, and facade green possess the highest hazard reduction potential.
• Passive and active cooling have to be considered in risk assessment and projections.

Traditional assessment of heat-related health risks neglects the influence of the building physics as outdoor conditions are used as predictor variables. Data on heat-related mortality from Berlin, Germany and from the US are evaluated with a risk concept which differentiates between outdoor and indoor hazards. Such, the influence of non-linear building physics on heat-related risks can be considered and the impact of adaptation strategies can be examined.The number of heat-related deaths in the age-group 65+ for Berlin is expected to double with each 1 K increase in ambient temperature. It can be reduced by 50% with a mean ambient air-temperature reduction of 0.8 K. Countermeasures to urban heat islands are evaluated according to their reduction potential on hazards, both indoors and outdoors. The analysis shows that classic UHI countermeasures, which are effective in reducing air-temperatures outdoors, do not necessarily reduce the indoor hazard. Regarding indoor heat-related hazards, trees, façade and roof greening, cool roofs and cool pavements have a low impact only. Measures at the building level, namely cool roofs and façade greening perform best, however, passive cooling and air-conditioning are most effective. To reduce the number of excess deaths in a changing climate, combined measures are necessary.