International Journal of Biometeorology
https://doi.org/10.1007/s00484-019-01782-2
SPECIAL ISSUE: SUBJECTIVE APPROACHES TO THERMAL PERCEPTION
Outdoor thermal comfort for pedestrians in movement: thermal
walks in complex urban morphology
Carolina Vasilikou 1,2 & Marialena Nikolopoulou 3,4
Received: 19 December 2017 / Revised: 26 July 2019 / Accepted: 5 August 2019
# The Author(s) 2019
Abstract
In the discussion of designing for a healthier city, people in movement between interconnected spaces perform a non-sedentary
activity enhancing sustainability and well-being. However, adverse weather conditions may create uncomfortable thermal
sensations that change or ruin the experience of people walking outdoors. This paper is presenting the findings of a 3-year study
on the perceptual variation of thermo-spatial conditions and comfort state for pedestrians moving between interconnected spaces.
Thermal walks were organised in two European pedestrian routes of 500-m length. The structured walks were conducted with
simultaneous microclimatic monitoring and field surveys of thermal perception based on 314 questionnaires, with a focus on the
variation of comfort states. The findings suggest that spaces in sequence do not affect significantly microclimatic variation but
have a large impact on the dynamic thermal perception of pedestrians. Interconnected spaces of high density result in a differentiation of thermal pleasantness between streets and squares. The aspect of movement along with complexity in urban morphology along a sequence enhances diversity in thermal sensation. This understanding opens possibilities in developing a
multisensory-centred urbanism, where the experience of the thermal environment plays an integral role for perception-driven
and healthier urban design.
Keywords Pedestrian movement . Spatial sequences . Thermal perception . Urban morphology . Environmental diversity .
Sensory urbanism . Healthier urbanism
Introduction
In the discussion of designing for a healthier city, people in
movement between interconnected spaces perform a physical
activity that promotes both sustainability (as a mode of transport) and well-being (in terms of physical health and social
interaction). During this activity, people gather multisensory
experiences that inform their state of comfort during their
* Carolina Vasilikou
K.Vasilikou@reading.ac.uk
1
Urban Living Research Group, School of Architecture, University of
Reading, Reading, UK
2
The Old Library Building, School of Architecture, University of
Reading, Reading, Berkshire RG1 5AQ, UK
3
Centre for Architecture and Sustainable Environment, Kent School
of Architecture, University of Kent, Canterbury, Kent, UK
4
Marlowe Building, School of Architecture & Planning, University of
Kent, Canterbury, Kent CT2 7NR, UK
navigation and wayfinding in the public realm. The latter
can be conceived as a series of urban entities (streets, squares,
widenings, suks, parks, water surfaces, etc.) that are
interlinked in a continuous urban sequence (forming a specific
route that is followed by pedestrians). In urban environments
that have stood the test of time, such as historic city centres,
these interconnected spaces create an intricate sequence of
perceptual experiences for people walking. From the interplay
of the multiple senses while walking outdoors, this paper focuses on the thermo-spatial environment outdoors and the
perceptual variations that occur due to the changes in the urban form as well as the microclimatic conditions at street
level. Variations in dynamic thermal perceptions due to a complex urban morphology and its microclimate have not been
addressed sufficiently. Following the sensewalking approach
(Henshaw et al. 2009), this study is based on the methodology
of ‘thermal walks’ (Vasilikou 2015, 2018) that investigates
pedestrian thermal perception through the analysis of the urban climate and spatial morphology. It is formed as a series of
focus group walks, where environmental monitoring happened hand-in-hand with people surveys. The new
Int J Biometeorol
methodology focuses on a point-to-point assessment of
thermo-spatial variations, combining the collection of objective microclimatic and spatial data with subjective responses
by people walking (Vasilikou and Nikolopoulou 2013).
Thermal comfort outdoors is predicted through the model
of thermal equilibrium. Although different models for the
prediction of outdoor thermal comfort have been developed
and used in the design of urban spaces, it is widely recognised
that the state of comfort may also be influenced by qualitative
parameters that are not included in the models based on the
thermal equilibrium (Brager and de Dear 1998). For example,
Aljawabra and Nikolopoulou (2009) highlighted the impact
of demographic factors (gender, age, culture, economic status); Ait-Ameur (2002) Ng (2012) and Chen and Ng (2012)
revealed the contextual parameters (building function, activities, climate, season); Henshaw et al. (2009) and Vasilikou
(2018) explored the multisensory and environmental interplay (thermal, aural, visual and olfactory); and Lenzholzer
et al. (2017), Lenzholzer and Koh (2010), Lam (2012) and
Nikolopoulou and Lykoudis (2007) brought to the surface
cognitive parameters (use, behavioural preferences and expectations), all of which play a critical role in the comfort
state for people walking. Other research has also demonstrated that in outdoor contexts particularly, where people have
limited control over their discomfort, thermal perception is
greatly influenced by the information that the person has in
a specific setting (Nikolopoulou et al. 2001). The above factors define Baker’s (2001) scope for adaptive opportunity and
thermal satisfaction outdoors. The latter is dependent on psychological factors (prior experience and time of exposure,
etc.; Nikolopoulou et al. 2001) as well as associated expectations and reasoned information (Knez and Thorsson 2006).
However, these factors cannot be evaluated solely based on a
quantitative approach (Lenzholzer et al. 2017).
Potvin (2000) showed that the sensory experience of the
urban continuum is produced in a dynamic state. The sequential nature of interconnected spaces enhances this dynamic perceptual mode through the actual motion between
spaces (Ouameur and Potvin 2007). Both studies assert that
wind and solar radiation are the main factors attributed for
variations in outdoor thermal comfort in any given period,
resulting to a wide range of combinations of environmental
diversity. The objective to achieve comfort during walking
needs to take into account both temporal and spatial variations, as well as opportunities for adaptation. Sensations may
include both momentous pleasant and unpleasant experiences. The body in motion itself plays an important role
for a comfortable thermal sensation, based on quality of
movement, evaporative cooling (production of sweat) and
metabolic rate. This paper investigates how people walking
in a sequence of irregular spaces may experience thermal
diversity through instantaneous variations with the potential
for reducing thermal discomfort. Part of a wider longitudinal
study, the aim of this paper is to present the differential
thermal experience of urban microclimate as induced by a
complex urban morphology in the spectrum of the temperate
climate (warm and cold). Evaluating the thermal comfort
conditions for pedestrians in movement, it provides an understanding of subtle changes in thermo-spatial conditions
between interconnected spaces of a spatial sequence. The
combined effect of urban morphology and materiality
(Table 1) during walking provides a multivariable description of pedestrian thermal perception that contributes to the
understanding of how to create more comfortable thermal
experience for people in movement and to inform the principles of multisensory and healthier urbanism.
The methodology of thermal walks
The assessment of the way walkers perceive thermal variations in urban spaces due to their physical activity relies on a
multiparametric analysis (Johansson et al. 2014). The interaction between embodied experience and the thermo-spatial
environment mediated by walking forms the basis of this
work. Two walking paths in temperate European sites were
chosen, both placed in the historic core of London, UK, and
Rome, Italy, representing popular everyday walking routes
(Fig. 1). This selection resulted in comparing interconnected
spaces with similar sequential geometric variations, at the
scale of the neighbourhood, in the wider context of temperate climate. The period of on-site primary data collection
took place in summer 2012 and winter 2013 in both cities
to evaluate variations between seasons. Each case study
comprised of a triptych of urban squares that are connected
with short segments of streets, with a comparable differentiation in their geometric descriptors (aspect ratio and sky
view factor). The London site starts at Seven Dials junction
up to Covent Garden square, passing through Neal and
James Street. The area is commercial with shops at the
ground floor and offices on upper floor, with scarce vegetation. Most frequent uses of space include people meeting
and pedestrian activities, with Covent Garden being the
main place attractor. The selected site is the longest continuous semi-pedestrian route in the historic core of London.
The equivalent route in Rome begins at Campo dei Fiori, an
open-air market place at daytime, to conclude in Piazza
Cairoli, one of the few urban squares with vegetation in
the historic centre. Via dei Giubbonari connects the beginning and end of the route and is a sixteenth century commercial street of Rome, with unwavering use. The selected
route is intersected in the middle by a small public space
that is entirely enclosed, Largo dei Librari. Pedestrian activities take place. The route is densely built with compact
blocks of buildings and narrow street segments.
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Table 1
Geometric descriptors at the scale of focus points for each of the thermal walks in Rome and London
Focus points of monitoring
Rome
London
Indicators at ‘focus point’ scale
Aspect ratio H/W
Sky view factor
Average albedo of surfaces
DoE (0–1)
DoE
(Steemers, 2004)
AR
0.45
0.54
0.2
0.2
4.85
BR
5
0.44
3.5
1.2
0.3 (0.5)
0.76
2.4
1.25
2.9
1.7
0.3
0.19
0.42
0.28
0.47
0.61 (vegetation incl.)
0.57
0.4
0.49
0.23
0.32 (vegetation)
0.52
0.2
0.2
0.2
0.2
0.27
0.2
0.19
0.2
0.21
0.2
0.2
0.08
0.16
0.19
0.22
0.38
0.74
0.09
0.54
0.11
0.17
0.26
11.71
5.95
5.23
4.57
2.65
1.35
10.75
1.85
8.94
5.77
3.8
CR
DR
ER
FR
AL
BL
CL
DL
EL
FL
Microclimatic monitoring
During the thermal walks, environmental monitoring took
place simultaneously with group surveys, to evaluate objective data at street level with subjective perceptions. A portable
weather station was fixed on an aluminium trolley with a
CR800 Campbell Scientific datalogger and five sensors
(complying with ISO 7726 1998) fixed on a telescopic pole
at a height of 1.75 m, to represent the average height of a
pedestrian. The environmental monitoring included Tair and
RH (using a CS215 probe with white radiation shield), Tglobe
(CT100 probe), wind velocity (ultra-sonic two-dimensional
anemometer) and illuminance (Skye lux meter). People completed a questionnaire during the simultaneous environmental
monitoring. Participants recorded their subjective thermal sensation at each focus point. An infra-red thermometer gun was
used to record surface temperatures of urban walls and
Fig. 1 The routes of thermal
walks in Rome (left) and London
(right) (source: Google Earth
2013 adapted by author)
pavement close to where participants were positioned.
Precise time-monitoring, constant during the days of monitoring, was accompanied by photographic documentation, showing the participants’ position next to the environmental equipment, and their position in the sun, shade and space in the
street.
Walking surveys
Participants were part of a thermal walking group, repeating
the walk at noon and at 2 pm. They were instructed to use their
own personal pace and stop at six focus points in order to
record their thermal sensation. The measuring device—a
moving feature in itself—did not interfere with the walking
pace of the participants. They were asked to evaluate their
reaction to the thermal environment when they would stop
in a square or in the middle of a pedestrian street, based on
Int J Biometeorol
the questionnaire. Participants assessed their thermal sensation and its variation as they moved through the spatial sequence from one point to the other. The questionnaire was
designed with a benchmark of actual sensation vote recorded
for every focus point of the walk. This facilitates the comparative analyses of ASVs between walking points, but also the
recording of the perceived differential ASV (dASV, i.e. the
variation in thermal sensation between two interconnected
urban spaces). The thermal walks questionnaire was developed including the evaluation of various aspects of thermal
perception: thermal sensation, wind sensation, sunlight sensation, perceived thermal comfort and differential thermal sensation (dASV), shown in Table 2.
Participants were randomly selected. The groups of participants consisted mainly of people working in the street, researchers and general inhabitants of the city, who were shortly
briefed about the nature of the research before the walk. An
open-ended question on the quality of space allowed for any
biased appreciations of the walks. They were studied in a natural
situation that would inherently involve walking, to evaluate their
perception of the thermal and spatial environment. The survey
was completely structured and prearranged with people from a
wide range of background that had given consent of participation
beforehand. In the structured questionnaire, the participants were
asked to concentrate on the variations that might occur between
different points of the walk, in terms of their thermal sensation,
preferences and characteristics of the space around them.
Overall 314 thermal walks questionnaires were completed
in London and Rome. Participants walked and evaluated their
thermal sensation, state of comfort and the surrounding space at
six different points along the given route, completing the relevant questionnaire section with both close- and open-ended
questions. The walks were repeated daily during the monitoring
periods at 12 pm and 2 pm, to evaluate the differences in the
thermal environment resulting from the effect of the solar angles and the sun and shade patterns in the space at different
times of the day. There were 5 to 10 participants per day, repeating both walks. The initial part of the questionnaire included completing general data about gender, age range, clothing
level to indicate clothing insulation and, finally, food and/or
drink consumption. General data concerning the time span of
the walk was completed by the researcher at the time of questionnaire collection. Due to the nature of the research that uses
sense-walking techniques, the engagement of participants on a
long-term basis (repeating the same walk twice in the same
day) and the duration of every survey (30–40 min), the recruitment of participants was challenging.
The study is based on a longitudinal approach with some
participants engaging in a dynamic assessment of their thermal perception (Table 3). Completed questionnaires are usually twice the number of participants, as 90% of those participated in both walks of the day of fieldwork. The age range is
fairly well represented with one peak at the category of 25–34.
Clothing levels for summer and winter conditions vary between 0.30–0.70 and 1.00–1.65 respectively which are considered appropriate for each season.
The microclimate of two spatial sequences
A series of graphs (and DEMs) show the combination of
multiparametric data that depict the variations in microclimatic
conditions (graphs (c) and (d)) and actual sensation votes
(graphs (a) and (b)) during the thermal walks. Figure 2 focuses
on the thermal walks in Rome during summer 2012 for every
minute of the walk from point A to point F at 12 noon and
2 pm. At 12 noon the most thermally pleasant variation
(approx. 60% of participants) occurred in spaces D (H/W = 6,
Table 2 The questionnaire was designed to record changes in the thermal sensation of pedestrians during their movement (in a 5-point scale: colder,
cooler, none, warmer, hotter) and perceived comfort condition
Question 1 (ASV)
How do you find the thermal environment at this precise moment?
Temperature
a) Cold
b) Cool
c) Neither warm nor cool
Wind
a) No wind
b) Breeze
c) OK
Sun
a) Would like more
b) OK
c) too much sun
Question 2 (dASV)
Do you feel a thermal variation in relation to your previous sensation?
a) Colder
b) Cooler
c) No variation
Question 3 (PTC)
You find this:
a) Uncomfortably cold
b) Uncomfortably cool
c) Comfortable
d) Warm
e) Hot
d) Windy
e) Too windy
d) Warmer
e) Hotter
d) Uncomfortably warm
e) Uncomfortably hot
Int J Biometeorol
Table 3
Participants’ descriptive sample for winter and summer walks in Rome and London respectively
Summer and winter participants—Rome (n = 94) (participants in daily walks = 79; in single walks = 15)
Gender
Summer
Winter
Age
Summer
Winter
Clo
Summer
Winter
Male
19
17
< 18
0
0
0.30–0.39
17
1
Female
33
25
18–24
25–34
35–44
9
21
6
3
18
9
0.40–0.49
0.50–0.59
0.60–0.70
1
26
8
12
26
3
45–54
7
6
55–64
6
3
> 64
3
3
Summer and winter participants—London (n = 79) (participants in daily walks = 69; in single walks = 10)
Male
Female
6
34
6
33
< 18
18–24
0
4
0
6
0.30–0.39
0.40–0.49
2
14
1
12
25–34
35–44
30
6
31
1
0.50–0.59
0.60–0.70
21
3
22
4
45–54
0
1
55–64
> 64
0
0
0
0
SVF = 0.18) and F (H/W = 0.4, SVF = 0.36). At 2 pm, more
than 60% of the same participants recorded space B (H/W = 8,
SVF = 0.11) as the space with the thermally pleasant variation.
As expected, air temperature and relative humidity remain
homogeneous throughout the walks. Wind velocity and solar
radiation/light intensity influence largely the variation in ASV of
participants between points. The collected data is coupled by two
maps (i and ii) that show the position of people during monitoring.
The digital elevation models show that 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 occurrence
of clear or overcast sky during the walk is shown by the blackand-white bank in the middle of the matrix in Fig. 2.
Similar analysis is shown for walks in Rome during winter.
Figure 3 shows the Largo dei Librari (C) (H/W = 0.9, SVF =
0.35) as one of the most thermally pleasant for both 12 noon and
2 pm walks. In colder conditions, the number of participants
(max. of 50%) that vote no variation in their thermal sensation
throughout the walk is increased (in comparison with a max. of
25% during warm seasonal conditions). The positioning of participants becomes non-relevant for winter conditions, as overcast
sky prevailed during the days of monitoring. In clear sky conditions, the sun penetration would not reach street level and thus,
sun/shade patterns were not taken into consideration in terms of
where the participants positioned themselves.
In the London case study (Fig. 4), summer variation in
ASV is non-homogeneous (that means that votes are divided
between cooler and warmer throughout walk), applying to
both daily walks. Neil square, located at a crossroad (H/W =
1.1, SVF = 0.41), received the votes for the highest change in
a thermally pleasant sensation (72% of participant voted a
warmer thermal sensation at 2 pm walk). Wind velocity and
solar radiation conditions were the main influence for this
perceptual variation. Transitions from higher to lower aspect
ratios (2.6 to 1.1) at 2 pm were voted as thermally more pleasant, warmer, during fairly overcast conditions and with wind
velocity decreasing from 1.5 to 0.8 m/s. In winter conditions
(Fig. 5) at 12 pm, Tair remains stable throughout the walk at
5 °C, while mean MRT remains below Tair values from points
A and B, while gradually increasing from point C until the end
of the walk. Points E and F present the highest means of MRT
at 6 °C and 8 °C respectively. A slight variation between
points occurs at the transition from point A to point B, with
an average ΔMRT of 2%. Average wind speed shows fluctuation during the walk with minimum value of 0.5 m/s and
maximum wind speed of 2 m/s occurring at point D. The small
range of values reflects the overcast conditions prevailing during the winter session of thermal walks. Average wind speed
at 2 pm shows slight fluctuation during the walk, with maximum value of 2.1 m/s occurring at point D and minimum
values of approx. 0.5 m/s at point F. There is slight variation
of 0.5 m/s during the transitions from points C to D (increase)
and from points D to E (decrease).
Perceived thermal sensation during walking
The two routes in Rome and London are characterised by a
similar variation in aspect ratio and sky view factor. However,
the effect of microclimatic differences is evident on people’s
perceived thermal comfort while walking. In winter, while
pedestrians in Rome found a comfortable thermal state during
their walk, in London the perception was predominantly uncomfortably cool for the duration of the walk. The effect is
Int J Biometeorol
a
b
Variation in Thermal Sensation
Rome in summer at 12 noon
100
Cold(er)
Cool(er)
Variation in Thermal Sensation
90
Cold(er)
Cool(er)
Warm(er)
Hot(ter)
Neither
90
Warm(er)
Hot(ter)
80
80
70
70
ASV Variation in %
ASV Variation in %
Rome in summer at 14 pm
100
Neither
60
50
40
60
50
40
30
30
20
20
10
10
0
0
A
B
C
D
E
F
A
B
C
Urban Spaces / Focus Points
c
D
E
F
Urban Space / Focus Points
Environmental diversity / Rome / summer
Mean / Tair
Mean / Tgl
Tmrt
OT
Mean / RH
60
40
A
B
C
D
E
F
A
B
C
D
E
F
35
55
50
25
Relave humidity (%)
Temperatures (C)
30
20
45
15
12pm
14pm
40
10
Sun
Shade
d
Mean / Wind
M
Mean / Lux
x
2.5
90000
80000
2
70000
50000
40000
1
Light Intensity (Lux)
Wind speed (m/s)
60000
1.5
30000
20000
0.5
12pm
14pm
10000
0
14:00
14:01
14:02
14:03
14:04
14:05
14:06
14:07
14:08
14:09
14:10
14:11
14:12
14:13
14:14
14:15
14:16
14:17
14:18
14:19
14:20
14:21
14:22
14:23
14:24
14:25
14:26
14:27
14:28
14:29
14:30
14:31
14:32
14:33
14:34
14:35
12:00
12:01
12:02
12:03
12:04
12:05
12:06
12:07
12:08
12:09
12:10
12:11
12:12
12:13
12:14
12:15
12:16
12:17
12:18
12:19
12:20
12:21
12:22
12:23
12:24
12:25
12:26
12:27
12:28
12:29
12:30
12:31
12:32
12:33
12:34
12:35
0
Time (m)
i
Fig. 2 Diagram of the factors connecting ASV, actual climatic data and
geometric descriptors of the summer thermal walks in Rome. Graphs (a)
and (b) show the variation in the ASV and H/W ratios; graphs (c) and (d)
ii
show the Tair, MRT, RH, wind speed and light intensity data; and maps i
and ii show the DEMs with positioning of participants
Int J Biometeorol
Variation in Thermal Sensation
Variation in Thermal Sensation
Rome in winter at 12 noon
100
Cold(er)
Cool(er)
Neither
90
Cold(er)
Cool(er)
Warm(er)
Hot(ter)
Neither
90
Warm(er)
Hot(ter)
80
80
70
70
ASV VAriation in %
ASV Variation in %
Rome in winter at 14 pm
100
60
50
40
60
50
40
30
30
20
20
10
10
0
0
A
B
C
D
E
F
A
B
C
Urban Space / Focus Point
D
E
F
Urban Spaces / Focus Points
Environmental diversity / Rome / winter
Mean / Tair
Mean / Tgl
Tmrt
OT
Mean / RH
20
80
B
C
D
E
F
A
B
C
D
E
F
75
10
70
5
65
Relave humidity (%)
Temperatures (C)
A
15
1
14pm
12pm
0
60
Sun
Shade
Mean / Lux
x
2.5
25000
2
20000
1.5
15000
1
10000
Light Intensity (Lux)
Wind speed (m/s)
Mean
n / Wind
5000
0.5
12pm
14pm
1
0
12:00
12:01
12:02
12:03
12:04
12:05
12:06
12:07
12:08
12:09
12:10
12:11
12:12
12:13
12:14
12:15
12:16
12:17
12:18
12:19
12:20
12:21
12:22
12:23
12:24
12:25
12:26
12:27
12:28
12:29
12:30
12:31
12:32
12:33
12:34
12:35
14:00
14:01
14:02
14:03
14:04
14:05
14:06
14:07
14:08
14:09
14:10
14:11
14:12
14:13
14:14
14:15
14:16
14:17
14:18
14:19
14:20
14:21
14:22
14:23
14:24
14:25
14:26
14:27
14:28
14:29
14:30
14:31
14:32
14:33
14:34
14:35
0
Time (m)
Fig. 3 Similar use of diagrammatic visualisation of data for the ASV variation (dASV) in winter Rome at 12 noon and how it is connected to the H/W
ratio of each focus point of the walk
Int J Biometeorol
Variation in Thermal Sensation
Variation in Thermal Sensation
London in summer at 12 noon
100
Cold(er)
Cool(er)
90
Cold(er)
Cool(er)
Warm(er)
Hot(ter)
Neither
90
Hot(ter)
ASV Variation (number of people) in %
Warm(er)
ASV Variation (number of people) in %
London in summer at 14 pm
100
Neither
80
70
60
50
40
30
20
10
80
70
60
50
40
30
20
10
0
0
A
B
D
C
E
F
B
A
D
C
Urban Spaces / Focus Points
E
F
Urban Space / Focus Points
Environmental diversity / London / summer
40
60
Mean / Tair
35
A
B
C
D
E
Mean / Tgl
Tmrt
F
OT
A
Mean / RH
B
C
D
E
F
55
25
50
Relave humidity (%)
Temperatures (C)
30
20
45
15
12pm
4
14pm
10
40
sun
shade/overcast
90000
2.5
Mean / Wind
M
W
Mean / Lux
M
80000
2
70000
50000
40000
1
Light intensity (lux)
Wind speed (m/s)
60000
1.5
30000
20000
0.5
12pm
14pm
0
10000
14:00
14:01
14:02
14:03
14:04
14:05
14:06
14:07
14:08
14:09
14:10
14:11
14:12
14:13
14:14
14:15
14:16
14:17
14:18
14:19
14:20
14:21
14:22
14:23
14:24
14:25
14:26
14:27
14:28
14:29
14:30
14:31
14:32
14:33
14:34
14:35
12:00
12:01
12:02
12:03
12:04
12:05
12:06
12:07
12:08
12:09
12:10
12:11
12:12
12:13
12:14
12:15
12:16
12:17
12:18
12:19
12:20
12:21
12:22
12:23
12:24
12:25
12:26
12:27
12:28
12:29
12:30
12:31
12:32
12:33
12:34
12:35
0
Time (min)
Fig. 4 The data collection of ASV, actual climatic data and geometric descriptors for London during summer
reversed for summer conditions: people’s perception in Rome
is divided between a comfortable and uncomfortably warm
state, whereas in London people voted for a consistently comfortable thermal experience throughout the walk.
Int J Biometeorol
Variation in Thermal Sensation
Variation in Thermal Sensation
London in winter at 12 noon
100
Cold(er)
Cool(er)
Warm(er)
Hot(ter)
Cold(er)
Cool(er)
Warm(er)
Hot(ter)
Neither
90
ASV Variation (number of people) in %
90
ASV Variation (number of people) in %
London in winter at 14 pm
100
Neither
80
70
60
50
40
30
20
10
80
70
60
50
40
30
20
10
0
0
B
A
D
C
E
F
B
A
D
C
Urban Spaces / Focus Points
E
F
Urban Space / Focus Points
Environmental diversity / London / Winter
Mean / Tair
Mean / Tgl
Tmrt
OT
Mean / RH
80
20
B
C
D
E
F
A
B
C
D
E
F
75
10
70
5
65
Relave Humidity (%)
Temperatures (C)
A
15
1
14pm
12pm
60
0
Sun
Shade
Mean / Lux
2.5
25000
2
20000
1.5
15000
1
10000
0.5
5000
12pm
1
14pm
0
12:00
12:01
12:02
12:03
12:04
12:05
12:06
12:07
12:08
12:09
12:10
12:11
12:12
12:13
12:14
12:15
12:16
12:17
12:18
12:19
12:20
12:21
12:22
12:23
12:24
12:25
12:26
12:27
12:28
12:29
12:30
12:31
12:32
12:33
12:34
12:35
14:00
14:01
14:02
14:03
14:04
14:05
14:06
14:07
14:08
14:09
14:10
14:11
14:12
14:13
14:14
14:15
14:16
14:17
14:18
14:19
14:20
14:21
14:22
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14:24
14:25
14:26
14:27
14:28
14:29
14:30
14:31
14:32
14:33
14:34
14:35
0
Time (m)
Fig. 5 The multivariable diagram for London thermal walks during winter conditions
Light Intensity (Lux)
Wind speed (m/s)
Mean / Wind
Int J Biometeorol
Fig. 6 Perceived thermal comfort
(PTC) and aspect ratio (H/W) of
the six focus points (A, B, C, D, E
and F) in Rome and London during winter
Looking at the variation of the thermal experience between spaces along the walk of Figs. 6 and 7, there are
subtle variations in the relation between perceived thermal
comfort (PTC) and the aspect ratio (H/W) of the six focus
points (A, B, C, D, E and F) in Rome and London. For
example, in London, during winter conditions, there is no
distinct tendency between PTC and aspect ratio (Figs. 6 and
7). However, despite the spatial homogeneity of the urban
fabric (low variation in aspect ratio between spaces), people’s responses show a higher variation in perceived thermal comfort between spaces than in Rome for the same
season (without a pattern emerging that differentiates
squares and streets). Two groups are created: points A, B,
C and D (uncomfortably cool) and points E and F
(uncomfortably cold). For Rome in winter, there are two
groups of sensations: in points C and F people responses
show a comfortable thermal experience, while points A, B,
D and E show a slightly uncomfortable experience.
Summer conditions show reversed patterns for the two cities. In Rome, a thermally comfortable experience is
achieved in spaces with higher aspect ratios (narrow
streets), whereas uncomfortably warm experiences are reduced when moving towards the end of the route to a square
with vegetation and presence of a water fountain (element
of ‘naturalness’). It is suggested that the beginning of the
walk, points A–C, forms one thermal experience, followed
by points D–F (more comfortable), due to both the effect of
urban morphology and the expectation of being in a space
Int J Biometeorol
Fig. 7 Summer variation in PTC
between focus points of the
thermal walk
with vegetation and natural shading. In London, the perceived thermal comfort state is fairly even throughout the
six different spaces. Here, street canyons seem to reduce the
perception of thermal comfort, mainly due to the lack of
Fig. 8 Actual sensation votes (ASV), dASV in Rome during summer and winter
Int J Biometeorol
Fig. 9 Summer and winter variation in ASV between focus points of the thermal walk in London
exposure to direct solar radiation and the orientation of the
street axis in parallel to the prevailing wind direction.
Variation in actual sensation votes in London
and Rome
Actual sensation vote (ASV) and its variation (dASV that
records colder, cooler, no variation, warmer or hotter effects)
across the length of the route show a noticeable change in the
thermal perception between the six focus points. Although in
both cities neutral ASV and dASV remain similarly low
(Figs. 8 and 9), specific spaces along the route result in changes in the prevailing thermal perception. For example, during
winter in Rome, the small, enclosed square in the middle of
the walk (point C) causes a warmer thermal sensation for the
majority of participants. This is reversed when people continue their walk in the shaded and narrow street canyon. In
London, the reverse pattern seems to occur. People record a
warmer thermal sensation when they move from an exposed
small square (point C) to the narrowest part of the selected
path (point D). This shows that irregularity in the urban fabric
can account for instances of thermal pleasantness along a
route.
Rome
Figure 8 presents the frequencies of the actual sensation votes
of participants for points A and F, along with the changes in
their thermal perception (dASV) for points B, C, D and E
during summer for both the 12 pm and 2 pm walks. During
summer walks, the majority of participants started the walk
with a thermal sensation of ‘warm’ (38%) or ‘hot’ (49%).
During the walk and the transition from squares to streets
and vice versa, 40–55% of participants felt ‘warmer’ or ‘hotter’ and 35–50% of participants felt ‘cooler’ while moving
from spaces B, C, D and E. The walk ended with 40% participants feeling ‘warm’, 15% participants feeling ‘hot’ and 35%
of participants feeling ‘cool’. Throughout the walk, at spaces
B, C, D and E, only 10–20% of participants did not perceive
any thermal variation. In total, no participant voted for a ‘cold’
or ‘colder’ sensation.
During winter conditions, participants voted the starting
point of Campo dei Fiori as ‘warm’ (40%), ‘cool’ (22%)
and ‘neither cool nor warm’ (38%). Participants finished the
walk with a ‘warm’ thermal sensation (40%), a ‘cool’ thermal
sensation (40%) and ‘neither’ at 20%. During the physical
transition along Via dei Giubbonari from point B to point E,
the thermal sensation of participants varied so that 25–50%
felt warmer, 10–50% felt cooler and 20–40% felt no thermal
variation. Interestingly, votes of ‘cold(er)’ thermal sensation
were not recorded by participants. This may be explained by
the wide range of daily air temperature during the fieldwork,
which ranged from 5 to 15 °C.
In addition, according to Fig. 8, there is pattern in the ASV
and dASV votes in winter conditions. Participants seemed to
vote for warm and warmer thermal sensations in spaces with
the morphological characteristics of a square (points A, C, E
and F) with votes ranging from 40 to 50%. This is consistent
with increased ASV and dASV votes of cool and cooler thermal sensations in narrow urban canyons, such as points B and
D. However, variations in microclimatic conditions from point
to point (as shown in Figs. 2 and 3) are significantly low.
While Tair and RH show no significant variation from point
to point (ΔTair = 0.15 °C and ΔRH = 2%), MRT shows a
variation of 0.1 °C, from point A to point B and a maximum
ΔMRT equal to 0.6 °C, when moving from point D to point E.
The same pattern may be observed for wind speed, although
the variation is significantly low (ΔWS = 0.1 m/s).
These relations between subjective responses and monitored
data may suggest that the participants’ thermal perception is
highly responsive to slight fluctuations in the microclimatic
conditions. At the same time, this relation could be further
investigated in terms of the morphological characteristics of
the spatial sequence.
London
Figure 9 shows the differentiation of thermal perception (ASV
and dASV) during the transition from one focus point to the
Int J Biometeorol
next one for summer and winter respectively for both 12 pm
and 2 pm walks. A high number of participants perceived the
thermal environment to be ‘neither cool nor warm’ (60%) at
the starting point A of the thermal walk in summer. This tendency for higher ‘neutral’ votes may be observed throughout
the walk. In the spatial sequence, thermal perception varies
significantly from one point to the other. Neutral votes show
an alternation of increased and decreased frequencies during
the walk. At point B, 19% of participants voted for ‘no variation’. At the same time, 59% of participants voted that the
transition from point A (square) to point B (street) resulted in a
cooler thermal sensation. This vote was reversed for point C,
where 32% of those questioned did not sense any thermal
variation and 58% found this transition warmer.
Interestingly, at point D (narrow street), participants’ votes
were divided between a cooler and a warmer thermal sensation (39% and 42% respectively), while ‘no variation’ vote
was reduced to18%. At points E and F, 30% of participants
sensed ‘no thermal variation’ and ‘neither cool nor warm’
respectively during the transition. At the same time, the movement from one space to another resulted in no significant
variation in the ‘cool(er)’ vote (48% and 38% respectively).
Interestingly, the extreme votes (cold(er) and hot(ter)) were
not selected by participants, except for a small minority of
2% who voted a hotter thermal sensation at point E. In terms
of variation, summer data show that narrow streets (H/W > 2)
may be linked to high frequencies of cooler thermal perception by those surveyed than squares in the given route.
However, for an urban canyon of H/W > 3 that may provide
at the same time both sunlit and shaded zones, participants
seem to be equally divided between a cooler and warmer
sensation. Finally, streets that possess the geometric characteristic of an oblong square (such as point E) and oblong squares
(point F) seem to produce a similar thermal sensation effect as
that of a narrower street, with high frequencies of a ‘cool(er)’
thermal sensation. That is in contrast with the prevailing thermal sensation and variation of centralised spaces (warm(er)),
such as the square in point C. In terms of no variation, narrow
streets, such as points B and D, share a low frequency of votes
(18%) by those questioned. This is in contrast to increased
frequencies at point C (square) and point E (wide street) where
32% found no variation in their movement from a narrow
street to a square or wide street.
During winter conditions, unaltered thermal sensation
votes are shown for a seasonal change of Tair equal to
12 °C. The exact pattern of variations is observed for each
focus point. However, it is interesting to point out the
higher frequencies of neutral votes (‘neither cool nor
warm’ and ‘no variation’) throughout the walk than the
one in summer fieldwork. This may suggest that cool climatic conditions in the winter period may flatten microclimatic variations or hinder their perceived variation by the
participants. At the same time, an increased percentage of
‘warmer’ dASV for point C is consistent for both summer
and winter microclimatic conditions. This might suggest
that a variation in the thermal perception which improves
thermal comfort (warmer is more pleasant sensation in the
cold temperate climate) may be found in the middle of the
walk at Neil Square (C).
From the opposite spectrum, Earlham street (point B)
shows consistently in summer and winter an increased percentage of participants that perceive a ‘cooler’ thermal sensation when moving to this street. Poor insolation might explain
this tendency. However, it shows an expected result: moving
from an open space where thermal sensation is thermally neutral according to at least half of the participants to a narrow
urban canyon which remains in shade for the larger part of the
day seems to produce a sense of thermally cooler feeling. It is
suggested that this may be due to sun exposure, the presence
of overhead protection and high vehicular traffic that contributes to anthropogenic heat production.
Finally, findings at point A confirm the significance of the
architectural arrangement of the urban space. Neutral votes are
voted at high frequencies for both summer and winter.
Surprisingly, during the winter walks, 68% of those surveyed
voted the thermal sensation as ‘neither cool nor warm’. This
may be attributed to the effect of walking activity prior to the
commencement of the thermal walk, but most significantly to
the presence of a canopy close to the positioning of the survey
group.
The geometric descriptors of the six focus points (A, B, C,
D, E and F) in Rome and London show subtle variations. It is
interesting to point out the deviations from the standard patterns of ASV-dASV in relation to aspect ratio during winter in
Rome, where the only outlier is point C, which is attributed the
majority of ‘warm(er)’ votes. In summer, points B and D
(streets) provide the ‘cool(er)’ effect, whereas point A is attributed with the majority of the negative spectrum of ASV for
the season. Similarly, in winter London (Fig. 9), point D provides the ‘warm(er)’ and ‘neither_no variation’ votes in contrast with the rest of the points. Finally, during summer in
London, point D provides an equal spectrum of middle votes,
whereas point C is attributed the ‘warm(er)’ ASV-dASV.
Comparison between cities
In order to understand the effect of urban morphology on the
average perceived thermal comfort (PTC), statistical analysis
is carried out, comparing average PTC variation in squares,
such as points A, C and F, compared with streets, such as
points B, D and E. Figure 10 shows the variation between
cities and seasons for the different interconnected spaces of
the thermal walks. During summer, the people walking in
Rome reported less thermal discomfort in streets than in
squares (t (50) = − 2.622, p = 0.012 and Mstr = 1.38 vs.
Msq = 1.22). This may occur due to the increased shaded
Int J Biometeorol
Fig. 10 Perceived thermal comfort between streets and squares in the two cities during summer and winter
parts of the street canyons and the effect of wind channelling. During winter time in Rome, squares were reported
more thermally comfortable than streets ((t (41) = 2.508,
p = 0.016 and Msq = 1.34 vs. Mstr = 1.18). This may occur
due to the increased solar exposure in the squares of the
route.
In London, the comparison between streets and squares
shows marginal differences. Squares are perceived as more
thermally comfortable in summer (t (33) = 1.981, p = 0.056
and Msq = 1.67 vs. Mstr = 1.54). However, PTC for both
urban entities, streets and squares show a relatively high
degree of thermal comfort. This may occur due to low
changes in the variation of aspect ratio between the interconnected spaces that resulted in low variation in the perception of thermal comfort. During winter no significant
differences between streets and squares were recorded (t
(34) = − 0.281, p = 0.780). Participants found the walk uncomfortably cool throughout the overall route. This may
occur due to the seasonal low temperature, as well as low
solar radiation that resulted to a relatively homogeneous cold
thermal sensation.
Conducting a one-way ANOVA (F (3, 158) = 13.522,
p = 0.000) for the four fieldworks in summer and winter
showed variations between the two locations, London
and Rome. Perceived thermal comfort did not show significant variation between summer and winter Rome (p =
0.000). In London, average PTC during summer was
higher the equivalent from Rome (p = 0.015), while average PTC in winter was lower (p = 0.007). This suggests
that outdoor thermal comfort is achieved in Rome during
both seasons due to the higher complexity of the urban
morphology and higher opportunities of urban surfaces to
be exposed in solar radiation. In London, only summer
walks showed opportunities for thermal comfort while
conditions in winter would require a mitigation strategy.
Conclusion
Observing dynamic thermal sensation in interconnected
spaces can reveal significant understanding about the impact
of intricate urban morphology on the microclimatic conditions and subsequent thermal perception of people in movement. The physical act of walking acted as a mediator in the
juxtaposition of objective monitoring of the thermal environment and the collection of subjective people responses. The
complexity of the study and its visualisation creates challenges to the urban designer. The thermal walks in the two
cities during two different seasons (summer and winter) reveal the reverse thermo-perceptual effect for each set of participants, mainly due to differences in air temperature.
Perceived thermal comfort was recorded for both locations,
with the thermal walk in London during summer showing the
higher rate of satisfied participants of all thermal walks. An
evident differentiation between streets and squares was recorded in Rome for both seasons, with the diversity of spatial
typologies providing the potential of thermal comfort according to the time of the year. This was not observed for the
London case study, where winter fieldwork was not done
under ideal conditions. In terms of morphological descriptors,
aspect ratio and its variation in the spatial sequence play the
foremost role in differentiating thermal comfort in squares
and streets (particularly in Rome). In summer, streets seem
to provide a higher potential of cooler conditions of thermal
Int J Biometeorol
variation than squares. However, the resulting thermal sensation still lies in the comfortable-uncomfortably-warm spectrum. Variation exists but it is subtle. Conversely, squares in
winter Rome provide a more thermally comfortable effect
during the walk.
Using case studies from the historic core of metropolises
provides the benefit of exploring unique urban spaces of continuous use in time. In these, the perception of thermal comfort
by pedestrians seems to derive from the opposite function of
adjacent spaces. It is not squares or streets that may be thermally comfortable. It is the variation created by the adjacency
of a street to an open space that may provide a thermally
interesting transition in the urban continuum.
Combining dynamic thermal experience and urban morphology revealed the need for more detailed quantitative and
qualitative description of urban entities in order to identify all
spatial characteristics that may result in a specific thermal sensation according to time of day and season. At the scale of the
spatial sequence, an intermediate scale between the urban entity and the neighbourhood, the degree of complexity seems to
determine the thermal diversity of the urban continuum. The
research has demonstrated that the use of thermal walks can
provide an in-depth knowledge of the role of irregular urban
forms in contributing to thermal diversity at street level.
Findings suggest a greater thermal diversity was found in the
urban texture of Rome, rather than in London. This understanding opens possibilities in developing a multisensorycentred urbanism, where the experience of the thermal environment plays an integral role for perception-driven design.
Acknowledgements The author would like to thank Simos Yannas from
the Architectural Association for hosting the portable weather station
during the London fieldwork and the informative discussions; Marina
Baldi, Ibimet Rome, Carmen Maria Beltrano, Ibimet Rome and Anna
Maria Siani, University La Sapienza, for support during the Rome fieldwork; and Gordana Fontana-Giusti for advice on urban design. Special
thanks are extended to all the participants in the surveys who made this
project possible.
Funding information The research was funded by the Academy of
Athens, and the travel for the field surveys was covered by the Faculty
of Humanities Fund, University of Kent.
Open Access This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the
Creative Commons license, and indicate if changes were made.
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