PLEA2013 - 29th Conference, Sustainable Architecture for a Renewable Future, Munich, Germany 10-12 September 2013
Thermal Walks:
Identifying pedestrian thermal comfort variations in the urban continuum
of historic city centres
CAROLINA VASILIKOU*, MARIALENA NIKOLOPOULOU
Kent School of Architecture / Centre for Architecture and Sustainable Environment, University of Kent, Canterbury, UK
ABSTRACT: The paper investigates the impact of urban morphology on the thermal comfort of pedestrians as they
move in the urban continuum of historic city centre neighbourhoods. Primary fieldwork carried out in two different
European locations, investigated the differentiation in the thermal sensation of pedestrians, during their walking
activity in a dense urban continuum. The new methodology, thermal walks, involved simultaneous environmental and
human monitoring. A series of structured walks with participants carried out in the summer and winter, took place in
parallel with measurements of climatic conditions in the different spaces of the designated route. Following the walks,
a sequential analysis identifies the variations that are perceived by users between spaces with different geometrical
characteristics, forming part of the urban continuum. The research provides a new analytical tool to identify the
diversity of thermal sensations that could be provided by a complex urban morphology.
Keywords: environmental diversity, pedestrian movement, thermal comfort, urban microclimate
INTRODUCTION
Walking is the most widespread mode of transport [1].
As a crucial link between intermodal transfers,
pedestrian activity helps to fulfil recreational and
utilitarian trips. Urban design and transport studies have
established the importance of thermally comfortable
outdoor spaces, which enhance vitality and liveability of
cities, for use by pedestrians [1, 2, 3].
This paper presents the initial results of a primary
fieldwork on pedestrian perception of the thermal
environment in the urban continuum. The wider aim of
the study is to provide an understanding of the dynamic
thermal comfort of pedestrians as they walk in
differentiated urban spaces and the impact of complex
morphology on their perception.
Two pedestrian routes in different European
locations were selected. They were situated in the
historic city centres of London, UK (51˚30’N, 0˚08’W)
and Rome, Italy (41˚54’N, 12˚30’E), representing
popular everyday walking routes and covering the range
of the temperate climate. This enabled the comparison of
two urban morphologies with similar sequential
geometric variations, at the scale of the neighbourhood,
in a different cultural and climatic context. The
fieldwork was carried out during summer 2012 and
winter 2013 in both cities to assess seasonal variations.
This paper presents initial findings of work in progress,
focusing on perceived thermal variations in the thermal
sensation of pedestrians as they walk in the urban
continuum.
WALKING AND THERMAL VARIATION
Pedestrians, in contrast with vehicular movement, can
only adapt to the circulation facilities provided for them.
In this context, walking satisfies the needs for the
smallest scale of transport and gives pedestrians a
unique capability for flexible and small scale
movements. People’s activities on foot involve a
substantial amount of meandering, sudden changes of
direction and stop and go movements. People often walk
consciously or unconsciously along places where it is
attractive and comfortable, be it in the shade in the
summer, or choosing a route with other people.
The way pedestrians experience the thermal
environment outdoors is based largely on the sensory
cues they pick up during their movement in the urban
continuum [4]. Microclimatic conditions and
environmental diversity seem to influence pedestrian
experience and perception of open spaces especially in
high density urban fabrics [2, 5]. The act of walking
itself can be analysed in a sequence of different spatial
and thermal experiences, with various intensities. The
variations between sequential urban spaces are
distinguished here in a) spatial, i.e. different urban
morphology, b) microclimatic, i.e. fluctuations in
temperature, wind speed, solar radiation, etc. and c)
perceived, i.e. the subjective experience and
psychological variables of pedestrians on assessing the
above physical variations.
METHODOLOGY
Previous studies have focused on the thermal sensation
of users standing or sitting in outdoor spaces [6]. This
study investigates variations in thermal comfort during
the dynamic state of pedestrian movement in a
comparative analysis of the thermal experience between
different urban spaces in a continuum. The sensitivity of
walkers for their environment and the effects of the
weather on their activity have to be taken into account
when assessing thermal perception. For this purpose, the
methodology used includes sense-walking techniques
[7] along with environmental and human monitoring.
Thermal Walks
The fieldwork was organised in structured walks
with participants walking along selected pedestrian
routes in the two cases study city centres. In each route,
a walking distance of approximately 500m or 20-25
minutes was covered. Participants were briefed in a prewalk meeting for the nature of the research, in order to
provide climate-conscious responses. The thermal walks
were repeated twice a day, at 12 noon and 2pm, to
record the diurnal variation at the time of the day were
pedestrian frequentation has been recorded through
observations as more elevated (lunch time). The
duration of each session in summer and winter was 5
days for each location.
included inhabitants, people working in the area and
visitors of all age.
The questionnaire included a section dedicated to
general observation data, such as age, gender, clothing,
etc. The second part consists of seven questions that
evaluate the thermal conditions, sensation, preference
and satisfaction of subjects. It also includes an
evaluation of the surrounding urban morphology. Four
sections followed, designed to provide a comparative
evaluation between the focus points of the walk. The
final part of the questionnaire provided an overall
assessment of the walk, aiming to link variations in
climatic conditions with different spaces along the route.
Tale of two cities: London and Rome
Two pedestrian study areas with similar variations in
their geometric descriptors were carefully selected in
two different latitudes (London, UK and Rome, Italy) to
represent respectively the cool and temperate climate
zone. Each route is characterised by three urban squares
that are connected with short segments of streets, with a
sequential differentiation in their geometric descriptors
(aspect ratio and sky view factor).
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Environmental Monitoring
During the thermal walks, a portable weather station
(Thelonius) was used to record the urban climate at
street level. It was comprised of a CR800 Campbellsci
datalogger on a lightweight trolley with five sensors
mounted and a telescopic pole at 1.75m, to simulate the
average walking person’s height. The environmental
parameters monitored were a) air temperature and
relative humidity (CS215 probe with white radiation
shield), b) globe temperature (CT100 probe), c) wind
speed (ultra-sonic two-dimensional anemometer), d) lux
levels (Skye lux meter), and e) carbon dioxide levels.
Thelonius monitored and recorded the variation in
microclimatic conditions continuously throughout the
given routes, with six focus points of recording.
Human Monitoring
Pre-walk observations were used to record patterns
of pedestrian movement along the selected case studies,
as well as frequentation times, through video recording,
people following techniques and people counting. In the
context of the thermal walks, participants were asked to
record their thermal sensation, preferences and
satisfaction by completing a structured questionnaire.
Walking simultaneously with the portable weather
station, participants focused on six points along the
route to record variations in their thermal sensation (in a
5-point scale: colder, cooler, none, warmer, hotter) and
comfort state. Participants were randomly selected and
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Figure 1: The two »case study routes in London (top) and
Rome (bottom).
The case study in London is the route from Seven
Dials junction to Covent Garden square, walking
through Neal and James Street (Fig. 1, top). It is a
commercial area with shops at the ground floor and
offices, with little or no vegetation. People meeting and
walking through are the most frequent activities, with
Covent Garden being one of the main destinations of
pedestrians. The case study is the longest continuous
semi-pedestrian route in the historic city centre of
London.
The selected route in Rome commences from Campo
dei Fiori, usually an open air market until noon, and
ends in Piazza Cairoli, one of the few urban squares
with vegetation in the historic core of the city (Fig. 1,
bottom). Via dei Giubbonari that connects the two
squares is one of the historic commercial streets of
Rome, with continuous use since the sixteenth century.
The street is intersected in the middle of the route by a
small fully enclosed square, Largo dei Librari. Similar
activities as with the London case study take place. The
urban morphology is characterised by dense, compact
blocks of buildings and narrow street segments with
frequent intersection of paved open squares.
RESULTS
This study presents initial results from the analysis of
the data collected in summer 2012 and winter 2013 in
Rome and in summer 2012 in London. The data from
the last fieldwork session in winter 2013 in London are
currently being processed in parallel with writing this
paper. Overall 314 questionnaires were completed
during the thermal walks in both locations. In Rome,
summer thermal walks involved 90 interviews and 90 in
winter, whereas in London 66 questionnaires were
collected in summer and 68 in winter.
London
Rome
Table 1: Average measured microclimatic conditions for the
two locations, Rome and London.
summer
Tair
(°C)
31.9
Tglobe
(°C)
32.6
RH
(%)
41
Ws
(m/s)
0.6
Light
(lux)
16310
winter
9.1
9.9
52
1.2
10649
summer
19.3
21.1
40
1.1
12900
winter
6.2
7
57
0.9
8900
The weather conditions that occurred during the
fieldwork are presented in Table 1. There is a significant
difference in air temperature for both Rome and London,
with mean summer air temperature of 31°C and 19°C
respectively. Winter mean temperature is more similar
for both locations, at 6-9 °C. Relative humidity is
similar for both locations, at 40% during summer and
52-57% during winter. Thermal preferences (Fig. 2)
differ between case studies and seasons. During
summer, participants in Rome prefer to be cooler (78%),
whereas in London, 56% of participants prefer to be
warmer and 40% prefer no change. In winter Rome,
67% of participants prefer to be warmer.
Figure 2: Thermal preferences in Rome (winter and summer)
and London (summer).
Variations in Thermal Perception
The thermal walks were iterated during five days
(including weekends), while, when possible, same
participants were interviewed for more than one day and
for both seasons. The focus of this longitudinal study of
thermal variations is on the link between three
parameters of the outdoor urban continuum: urban
morphology, microclimatic conditions and perception of
pedestrians.
Figure 3 presents a matrix of graphs and DEMs that
show a holistic view of the three parameters for the
walks taking place in Rome summer 2012. Graphs (a)
and (b) show the variation in the Actual Sensation Vote
(ASV) of participants as they walked from focus points
A to F at 12 noon and 2 pm respectively. It is shown that
at 12 noon the most thermally pleasant variation
(approx. 60% of participants) occurred in spaces D
(H/W=6, SVF=0.18) and F (H/W=0.4, SVF=0.36). At
14pm, more than 60% of the same participants recorded
space B (H/W=8, SVF=0.11) as the space with the
thermally pleasant variation. These results can be related
to the actual climatic conditions that were monitored in
parallel (Graphs (c) and (d) in Figure 3 show the
climatic conditions for the 12 noon and 2 pm walks). As
expected, air temperature and relative humidity remain
homogeneous throughout the walks. Wind speed and
solar radiation / light intensity have the greatest impact
on the changes in ASV of participants for each focus
point.
Finally, the Digital Elevation Model (DEM) for the
Rome case study (Fig. 3, maps i and ii) show the
positioning of participants during the monitoring. Due to
the urban morphology and solar angle, at 12 noon 40%
of participants were positioned in the sun (even in
spaces with H/W>2.5), while at 2 pm 93% of
participants walk in shade. The black-and-white band in
the middle of Figure 3 illustrates the sun-shade pattern at
the two different times of the walks.
(a)
(b)
(c)
(d)
(i)
(ii)
Figure 3: Matrix of the three parameters shows the relation between the ASV, actual climatic data and geometric descriptors of
the summer thermal walks in Rome. Graphs (a) & (b) show the variation in the ASV and H/W ratios, graphs (c) & (d) show the
Tair, MRT, RH, Wind speed and light intensity data and maps i and ii show the DEMs with positioning of participants.
Similar analysis is carried out for winter thermal
walks in Rome. Figure 4 shows focus point C
(H/W=0.9, SVF=0.35) as one or the more thermallypleasant for both 12 noon and 2 pm walks.
At the same time, in winter there is an increase in the
number of participants (max. of 50%) that record no
variation in their thermal sensation throughout the walk
(compared with a max. of 25% during the summer).
(a)
(b)
(c)
/Overcast
(d)
Figure 4: Multi-parametric matrix shows the relation between the ASV, actual climatic data and geometric descriptors of the
winter thermal walks in Rome. ASV variation in winter Rome at 12 noon is related to the H/W ratio of each focus point.
As shown, temperature and RH remain fairly stable
throughout the walks. Light intensity data are used for
indicating sunny, shady or overcast conditions.
Compared wind and light intensity mean data (summer
and winter respectively) with thermal sensation votes in
Rome suggest that transitions from H/W>2.5 to
H/W<2.5 increase non-homogeneous (either warmer or
cooler) variations in ASV. Low wind speed seems to
allow for more homogeneous thermal sensation votes
(for example, in summer Rome at 12 noon 67% of
participants found the transition from H/W=0.9 to
H/W=6 as thermally cooler, while wind speed reduced
from 1.6 to 0.6 m/s).
During the London summer walks (Fig. 5), variation
in ASV seems to be non-homogeneous (i.e. distributed
between cooler and warmer for the duration of the
walk), for both the 12 noon and 2 pm walks. Space C, a
small square in a crossroad (Earlham and Neil street;
H/W=1.1, SVF= 0.41) shows the highest thermallypleasant variation (72% of participant recorded a
warmer thermal sensation at 2 pm walk). Wind speed
and sunny or shady/overcast conditions (not shown
here) were the main climatic parameters of this
variation. Transition from H/W=2.6 to H/W=1.1 at 2pm
was recorded as thermally-more-pleasant, warmer,
during fairly overcast conditions and while wind speed
reduced from 1.5 to 0.8 m/s).
CONCLUSION
This paper presents initial findings from the study of
environmental diversity and pedestrian thermal comfort
in the continuum of complex urban spaces. The
fieldwork presented shows a tendency for pedestrians to
be able to perceive and identify consciously the
variations of microclimatic conditions, while walking.
Participants seemed to associate climatic variables with
specific urban spaces along their given walking route.
Initial findings suggest that thermally-pleasant spaces do
not share a specific geometric characteristic and may
vary between seasons (for example, in summer Rome,
H/W=6-8, whereas in winter, H/W=0.4-0.9).
Further analysis that will quantify this differentiation
using climatic simulation is currently under way.
Predicted climatic models, based on the complex urban
morphology under consideration will be compared with
the findings of the primary research. Further conclusions
will provide a detailed understanding of the perceived
variations in the thermal experience of pedestrians
walking in a complex urban continuum.
Figure 5: ASV variation during walks in London (summer).
Urban Spaces of Thermal Preference
Part of the interviews addresses the way participants
perceived the change in the surrounding spaces as they
moved from one focus point to following one. At the
end of the walk, an overall evaluation was included.
Each participant was asked to record the most pleasant
and unpleasant climatic variable and to identify the
space in which they experienced it. For example, Figure
6 shows the spaces that were thermally-more-pleasant in
summer and winter in Rome.
In Rome, Piazza Cairoli (point F), the square with
vegetation and water features, was voted as the space
with the most pleasant thermal aspect for both seasons
(Fig. 6). The results of the end-of walk evaluation of
thermally-pleasant spaces seem to correspond to the
findings from the multi-parametric matrix analysis of the
thermal walk and the variation in ASV (Fig. 3 & 4).
Figure 6: Thermally-most-pleasant spaces according to
participants in Rome during summer and winter walks.
ACKNOWLEDGEMENTS
Acknowledgements are due to Prof. G. Fontana-Giusti
for her help in identifying the London case study, Prof.
S. Yannas from the AA School, London for his help in
recruiting participants and overnight storage of
equipment, Dr. M. Baldi from CNR-Ibimet Rome, Dr.
C. Beltrano from CRA-CMA Rome and Dr. A.M. Siani
from University La Sapienza, for sharing weather data
and participating in the thermal walks fieldwork.
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