In this study, an assessment of the intensity of the urban heat island (UHI) in Rotterdam was carried out using an innovative mobile bio-meteorological measuring platform mounted on a cargo bicycle. The goal was to assess whether or not heat stress is currently or likely to become a critical issue. Physiological equivalent temperatures were calculated directly from the measurements. Preliminary results show how effective urban parks and greenery are in reducing the UHI. The maximum UHI was about 7 K warmer than the rural area, whereas greener urban configurations were under 3 K warmer. City parks show marked cooling effects during daytime. The preliminary results clearly demonstrate the presence of a considerable UHI in Rotterdam, which is expected to be found in other Dutch cities, and confirms the important role of green spaces in mitigating urban heat stress

Elbers, J.A.

Heusinkveld, B.G.

Holtslag, A.A.M.

Hove, L.W.A., van

Jacobs, C.M.J.

Moors, E.J.

Steeneveld, G.J.

English

Wageningen Yield 

 433
Use of a mobile platform for assessing urban heat stress in Rotterdam 
 
Bert G. Heusinkveld
1
, L.W.A. van Hove
1,2
, C.M.J. Jacobs
2
, G.J. Steeneveld
1
, J.A. El-
bers
2
, E.J. Moors
2
, A. A. M. Holtslag
1
 
 
1Department of Meteorology and Air Quality, Wageningen University, The Netherlands 
2Earth System Science and Climate Change Group, Wageningen UR, The Netherlands 
 
Abstract 
In this study, an assessment of the intensity of the urban heat island (UHI) in Rotterdam was 
carried out using an innovative mobile bio-meteorological measuring platform mounted on a 
cargo bicycle. The goal was to assess whether or not heat stress is currently or likely to become 
a critical issue. Physiological equivalent temperatures were calculated directly from the mea-
surements. Preliminary results show how effective urban parks and greenery are in reducing the 
UHI. The maximum UHI was about 7 K warmer than the rural area, whereas greener urban 
configurations were under 3 K warmer. City parks show marked cooling effects during daytime. 
The preliminary results clearly demonstrate the presence of a considerable UHI in Rotterdam, 
which is expected to be found in other Dutch cities, and confirms the important role of green 
spaces in mitigating urban heat stress.  
 
1.  Introduction 
The majority of the world’s population now live in urban environments. The average 
temperature of built-up areas is higher than the surrounding rural area, which enhances 
heat stress, and is called the Urban Heat Island (UHI) effect (Oke, 2006). Because The 
Netherlands has a mild Cfb climate and is situated close to the sea, it was never consi-
dered an issue for urban planning even though the level of urbanization began to in-
crease rapidly. Currently the built-up area is over 15% of the total land area and increas-
ing. Recent heat waves of the year 2003 and 2006 caused an excess in mortality in The 
Netherlands of between 1400 and 2200 people.  Climate projections predict that heat 
waves in The Netherlands will likely become more frequent in the next decades, which 
will compound the environmental stresses of urban life and lifestyles.  However, infor-
mation regarding UHI in Dutch cities is completely lacking, both from observational 
and model perspectives, which hampers the design of suitable adaptation and heat miti-
gation strategies. Even moderate heat waves should not be underestimated for a mari-
time climate. The reason is that the population has no time to acclimatize since adapta-
tion of human thermoregulation usually takes about 1 week. 
Spatial planning and urban growth projections using various scenarios all point to a 
large expansion of urbanized space (Nijs et al., 2002). The scenarios of the Dutch Na-
tional Nature Outlook study (MNP, 2002) which are based on various IPCC-scenarios, 
also supports this. Comparing these scenarios to the current situation (2010), urban 
growth seems to follow the ‘Global Market’ scenario. This scenario suggests strong 
population growth, free trade, strong technological developments, limited role of gov-
ernment, strong decrease in agricultural land and a luxury consumption pattern. The 
most important land use changes in The Netherlands over the last 10 years are related to 
the increase of urban and nature reserve lands at the expense of agricultural land (Ha-
zeu, 2006), and mixing of different land-use types in both urban and rural areas (Ritse-
ma et al., 2006. The Land Use Scanner tool (LUS) was used to simulate how The Neth-
erlands land use would look like in 2040. The LUS is a GIS-based logit model that si-
 434
mulates future land use (Hilferink and Rietveld, 1999) and  has been used for various 
policy-related research projects. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 1:  Land use scenario, left side year 2000, right side year 2040 
 
The ‘Global Market’ scenario simulation estimates 20 % urbanization in 2040 (Fig. 1). 
The definition of urban space also includes infrastructure and industry but there are 
some differences in the definition and the Dutch planning office includes, for example, 
urban greenery and urban infrastructure but not external infrastructure. The impact of 
infrastructure on surface heating is significant and therefore should not be excluded 
from such analyses.  
This study examines the extent of the urban heat island effect (UHI) of the city of Rot-
terdam, which is part of the largest urban conglomeration of The Netherlands with more 
than 1.2 million inhabitants on 870 km
2
.  
 
2.  Materials and methods 
Traverse measurements were performed in Rotterdam using two cargo bicycles as a 
mobile platform, equipped with innovative instruments to quantify the micro-
meteorological conditions inside urban canyons. The cargo bicycles greatly facilitated 
data acquisition through the narrow streets and urban canyons of pedestrian areas. The 
bicycles were equipped with a shielded thermometer, a humidity sensor, a 2-
dimensional sonic anemometer and 12 radiation sensors to measure solar radiation and 
thermal infrared radiation exchange from six directions (Fig. 2). Wind speed measure-
ments were corrected for bicycling speed. 
 
100 km
 435
 
Fig. 2: Mobile biometeorological station mounted on a cargo bicycle 
 
The data were recorded at 1 Hz and combined with concurrent readings from a GPS 
device. The instruments were powered by a solar panel mounted on the baggage carrier. 
Measurements were performed along two previously determined routes through a num-
ber of characteristic urban districts, including an industrial area, an older residential 
area, a city park and a harbour area. The routes were photographed at fixed intervals 
from 0.5 m above the ground with a fisheye lens pointing upwards. The observations 
were carried out during three 2 h time intervals on 6 August 2009. This was a warm day 
with maximum air temperatures of about 30°C. Data from the traverse measurements 
were compared with recordings from a nearby synoptic weather station outside the ur-
ban area. Fig. 2 shows a detailed view of the front of the bicycle. 
A very important factor in the human energy balance is the mean radiant temperature 
(TMRT), and this can be calculated directly from the 12 radiation sensors and correlates 
very well with perceived human comfort (Matzarakis et al., 2007) (Eq. 1). 
15.2734  !
"#
a
MRT
Q
T                                                                                           (1) 
Where Qa is the total shortwave and thermal radiation absorbed by the human body (W 
m
-2
),   is the thermal emissivity (-) and   is the Stefan Boltzmann constant (W m
-2
 K
-4
). 
Directional dependant weighing factors and shortwave radiation absorption coefficients 
need to be considered for calculating radiation load on a human.  
The advantage of these extensive measurements are that the human micro-climate can 
be quantified using physiologically relevant indices that are much more accurate than 
indices derived from standard weather station data. Examples include the physiological-
ly equivalent temperature (PET) (Höppe and Mayer 1987) or predicted mean vote 
(PMV) (Fanger, 1972). PET is defined as the physiological equivalent temperature at 
any given place, and thus complex outdoor microclimates can be compared with a cli-
mate chamber with temperature of air,  floor, walls and  ceiling at PET temperature 
(wind speed 0.1 m/s and relative humidity of 50%).  The higher accuracy for human 
micro-climate indices derived from such a mobile station is mainly related to its ability 
to measure omnidirectional radiative fluxes. These flux measurements determine TMRT, 
which is the most important meteorological parameter for calculating the human energy 
balance under summer conditions (Clark and Edholm, 1985).  
 
 436
3.  Preliminary results and discussion 
An initial analysis shows that the UHI is very large after sunset with an air temperature 
difference of more than 8 K between city center and rural environment (grassland). An 
interesting observation was an industrial zone with dark flat roofs. This area appears to 
have the hottest surface temperature of all urban areas in Landsat thermal infrared im-
ages. However the bicycle measurements did not find this area hotter than the city cen-
ter, especially not during the evening hours. This might be related to the low thermal 
inertia of the flat roofs. The UHI is strongest after sunset and gradually declines during 
the night. Air temperature remains higher than the rural area due to the slow release of 
solar heat storage originating from daytime solar radiative forcing.  
 
 
 
 
 
 
Fig. 3: Traverse measurements of Rotterdam, PET, Upper panel 14:00-16:00 h. lower 
panel 22:00 – 24:00 h (Central European Time) 
 
5 km 
 437
PET (Fig. 3) could be easily calculated because of the direct measurements of all the 
radiation components. Rayman software was used to compute PET without the need to 
calculate complex city canyon radiation distribution  because TMRT was measured on the 
bicycle (Matzarakis et al., 2007). The measurements show some interesting features. A 
park in the southeast side was the coldest spot during daytime whereas a neighborhood 
just east of the city center was the coolest urban spot during the evening hours. Both 
routes were documented using fish-eye photography. 
An isolated tree in an urban canyon does not seem to have much influence on PET dur-
ing evening hours (Matzarakis et al., 2007). However the bicycle data shows that a 
neighborhood with scattered trees does have a marked impact on air temperature during 
evening hours. On the other hand, a nearby park shows the opposite, which may be re-
lated to the closed canopy cover. This is also evident in the calculated PET.  
 
4.  Concluding remarks 
In a changing climate and with future urban space projection scenarios showing Dutch 
urban density increasing from 14% in 2000 to 20% by the year 2040, it is likely that the 
UHI impact will become much more serious. The UHI effect may also accelerate even 
faster because many isolated and growing urban clusters will start to influence each 
other, an issue worthy of further investigation. 
The presented biometeorological measurements using a cargo bicycle proved to be a 
valuable tool for investigating urban biometeorological conditions. While traversing the 
city of Rotterdam PET ranged from 25 to over 50 °C during a hot afternoon (6 August 
2009). The neighborhood with the lowest PET during daytime and evening hours ap-
pears to be an urban configuration with low buildings and extensive greenery.  
 
Acknowledgements 
This research was part of the project “Heat stress in the city of Rotterdam” (HSRR05) funded 
by the first phase of the Knowledge for Climate Program and the municipality of Rotterdam. 
We also like to thank the students Joel Schröter, Marina Sterk and Suzanne Visser for their sup-
port on the measurement days. 
 
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Author address: 
Dr. Bert G. Heusinkveld (bert.heusinkveld@wur.nl) 
Dept. of Meteorology and Air-Quality, Wageningen University 
Droevendaalsesteeg 4, P.O. Box 47, NL-6700AA Wageningen, The Netherlands 
 
  


Characterising urban concentration and land-use diversity in simulations of future land use. Ann Reg Sci

Land Use Scanner: An integrated GIS based model for long term projections of land use in urban and rural areas, in:

Man and his thermal

Modelling Radiation fluxes in simple and complex environments – Application of the RayMan model.

Nationale Natuurverkenning 2, 2000–2030, Milieu- en Natuurplanbureau/Kluwer, Alphen aan de Rijn Oke,

The physiological equivalent temperature -a universal index for the biometeorological assessment of the thermal environment.

Use of a mobile platform for assessing urban heat stress in Rotterdam

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van Hove, L.W.A.

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Use of a mobile platform for assessing urban heat stress in Rotterdam

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