The heat wave of 2006 caused an extra 1000 deaths in the Netherlands. That qualifies it for fourth place on the list of natural disasters causing the most deaths in that year. The daily death rate during heat waves in Europe is 30 percent higher than during other periods. And yet the issue of heat is not taken terribly seriously. Many of us enjoy a bit of heat. Heat has an image problem, partly because up to now it was not possible to establish objectively at what point heat becomes problematic. Together with the Dutch meteorological institute KNMI and consultancy bureau Witteveen + Bos, the Meteorology and Air Quality chair group has come up with a solution to that.
A new method expresses the heat sensitivity of a neighbourhood or suburb in a figure called the Urban Climate Index. This makes it possible to see at a glance whether the neighbourhood is in the danger zone and what steps could be taken to make it more heat-proof. By planting more vegetation, for instance. The method is based on the only truly objective and readily available yardstick for wellbeing: the death rate. Death is at the top of a pyramid of ailments and discomforts caused by heat and air pollution. All these discomforts are hard to measure, but death is not. The scientists also found a link between heat and the physical infrastructure of a neighbourhood: the height of the buildings, the width of the streets and the amount of green space and water.
Between them all these factors determine how hot it gets on a warm day in the city. Gert-Jan Steeneveld (WU) and project leader Ronald Groen (Witteveen + Bos) made a model for this. Correlated with the national death rate figures, it becomes possible to calculate a relative risk of dying as a result of exposure to a heat wave per neighbourhood. That risk is substantial. Heat waves in highly built-up neighbourhoods double the chance of dying. Is a risk like that acceptable? The researchers address that question by linking the combined effect of heat and air pollution to the European norm for risk of death from ozone. ‘You can now say: this neighbourhood is this far above the limit of what is acceptable,’ explains project leader Groen. ‘That question is now being answered for the first time. You can quantify heat sensitivity, which makes it easier for decision- makers to deal with. We can indicate objectively whether and how many measures are needed.’