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Extension and validation of heat island effect indicator

Issue 27-09-2018Rising temperatures lead to heat stress, possibly resulting in excess mortality. Due to climate change, exposure to excessive heat may double already by 2030, especially in cities and the eastern part of Flanders.

Heatwaves double due to climate change

Heatwaves are most frequently recorded in urban centres and farther away from the coast. Rising temperatures lead to heat stress, possibly resulting in excess mortality. New high-resolution model maps for Flanders show that as a result of global climate change, exposure to heat above health thresholds may double already by 2030. This is the outcome of a new MIRA research report.

Detailed survey of the heat problem 

This is the first detailed Flanders-wide survey of the heat problem, both for the current climate and under different climate scenarios until 2100. First of all, temperature measurements were made and analysed in and around 6 cities (Antwerp, Bruges, Brussels, Ghent, Hasselt and Lier). Cities do in fact behave as heat islands. Much higher temperatures tend to be recorded in urban areas than in their rural surroundings, especially during summer nights. As a result, cities experience more heatwaves with day temperatures in excess of 29.6 °C and night temperatures not dropping below 18.2 °C, for at least three consecutive days.

After validation based on temperature measurements in and around the above six cities, a set of high-resolution (100 m) maps was created for the purpose of identifying local hotspots. The survey results led to the following conclusions:

  • Under the current climate, the heat stress risk in urban areas is on average almost twice as high as in more rural areas. The larger the city, the higher the heat effect. Also the distance to the coast and the soil composition play an important role: in Limburg, temperatures are higher than in West Flanders due to a combination of lower average wind speeds, the presence of dry sandy soil and the greater distance away from the moderating influence of the sea (Figure 1).
  • Due to climate change, more places will in the future almost annually see heat levels that, until now, occurred only in the centres of our largest cities during exceptionally warm summers.
  • Under a low climate scenario, the number of heatwave days in an average year will increase from the current number of 4 to 7 in 2100. Under a high climate scenario, which can no longer be excluded, the number of heatwave days will already increase to 11 by 2030, 18 around 2050 and 50 by the end of this century (Figure 2).
  • Heat stress affects mainly young children aged up to 4 years and people aged 65 and over. The heat stress experienced by an individual is also determined by parameters other than temperature. Measures to keep the health impact of heatwaves under control include the provision of adequate air circulation, shaded areas, provision of drinking water, etc. Plus, of course, raising the awareness of the population to this problem.

Figure 1: Map with high-resolution distribution of occurrence of number of heatwave days under current climate (Flanders, 2000-2016)

Map with high-resolution distribution of occurrence of number of heatwave days under current climate

Figure 2: Evolution of number of heatwave days per year under different climate scenarios until 2100 (Flanders)Maps Evolution of number of heatwave days per year under different climate scenarios until 2100 (Flanders)

Read the English summary of the Dutch report ‘Extension and validation of heat island effect indicator’

Study commissioned by MIRA, Flanders Environment Report
Research report MIRA/2018/01

researchers: Dirk Lauwaet, Koen De Ridder, Bino Maiheu, Hans Hooyberghs, Filip Lefebre, VITO

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