Reseachers at Wageningen University and Research Centre (WUR) have been riding around Rotterdam and Arnhem in the Netherlands on two trikes mapping and measuring the urban climate during four time intervals on a 24 hour day. The measuring was to study the Urban Heat Island (UHI) effect that often causes heat stress.
The measurements on 6 August in Rotterdam showed that during day time the city centre was two degrees warmer on average than Zestienhoven(Rotterdam) airport, which is located outside the city. A striking observation was that the city park De Twee Heuvelen was 2.4 degrees cooler than Zestienhoven. This means that the differences in the afternoon in the city can rise to 4.4 degrees centigrade. During the late evening (22-24 hours), the city centre was more than 5 degrees warmer than Zestienhoven. The route near the national Green Heart (Doenkade) turned out to be even cooler (2 degrees C) than Zestienhoven. The difference in temperature between the city and countryside consequently amounted to more than 7 degrees during nocturnal hours.
In the late afternoon the felt air temperature – the air temperature perceived by the human body – was 28 degrees C at Zestienhoven, the temperature at the city centre of Rotterdam (in the sun and out of the wind) would feel more than 6 degrees higher – so well above 30° C. Surprisingly, similar effects were measured in the much smaller city of Arnhem.
For the measurements (before sunrise, midday, late afternoon, after sunset), days with maximum temperatures above 25° C were necessary. With the two cargo bikes with measurement equipment, the researchers cycled along two previously determined routes through a number of characteristic urban districts, such as an industrial area, an older residential area, a city park and the harbour area. The researchers plan to take more measurements later this year and in 2010.