Heat stress
Heat stress in the Netherlands
Human exposition to excessive warm temperatures is increasingly becoming a public health problem. Urban areas are especially vulnerable to heat stress since they concentrate large amounts of population and since they lack of resources to mitigate high temperatures. The heat stress in the Netherlands is caused by heat waves, but this problem is worsened in urban areas due to the heat island effect. That would affect more than 40% of the Dutch population.
Heat waves
Heat waves are prolonged periods of excessively hot weather. The KNMI defines heat wave as a situation of at least five consecutive days on which the maximum temperature is 25.0 掳 C or superior; wherein the maximum temperature is 30.0 掳 C or superior for at least three days. The KNMI registered at least 18 heat waves in the Netherlands since 1901. Global warming already made heat waves more frequent in the Netherlands. Since the year 2000 the observatory in de Bilt already registered 8 heat waves and the KNMI expects heat waves to occur more often and more intensively due to global warming.
Heat island
The defines heat island as the built up areas that are hotter than nearby rural areas, that effect is especially stronger during nocturnal hours. When the weather is clear and calm, nocturnal temperature differences of 3-5 掳C are normal, but differences of 8-10 掳C are also experienced.Heat islands are unlikely to affect much urban environments during the year. However, during summer and especially in combination of heat waves, the urban heat island effect can rise the temperatures to dangerous levels. High temperatures can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.
Heat island effect
The main cause of the heat island effect is the extreme heating of surfaces and materials in urban areas and the lack of cooling due to evaporation. The lack of vegetation is a main driver of the heat island effect. Vegetation intercepts radiation and produces shade that also contributes to reduce urban heat release. There are secondary causes of the urban heat island effect such as production of heat by traffic and human activity. Another reason that contributes to the urban heat island effect is the urban geometry. The positioning of buildings may 'intercept' solar radiation and block wind. Read more about the heat island effect on the .