Theor Appl Climatol (2009) 95:279–289
DOI 10.1007/s00704-008-0006-8

ORIGINAL PAPER

Evaluation of urban thermal environments in commercial
and residential spaces in Okayama City, Japan,
using the wet-bulb globe temperature index
Y. Ohashi & T. Kawabe & Y. Shigeta & Y. Hirano &H. Kusaka & H. Fudeyasu & K. Fukao

Received: 5 February 2007 / Accepted: 30 December 2007 / Published online: 24 April 2008
# Springer-Verlag 2008

Abstract We estimated wet-bulb globe temperature(WBGT) using measured meteorological data to understandthe bioclimates of human living spaces during the summer
season. Our research focused on commercial and residential
areas of Okayama City, Japan (population ∼700,000). The
commercial spaces (CO) mainly consisted of multi-story
office buildings, whereas the residential spaces (RE)
consisted of one- or two-story residential buildings. On afine day with southeast winds, the spatially averaged
WBGT measured in the CO was higher than that in the
RE. The difference was statistically significant and would
have caused noticeable discomfort and a high risk of heatdisorder for occupants of the CO over the long term. For
instance, at 1900 Japan Standard Time (JST), the maximum
difference in the WBGT between the CO and RE sites was
2.0°C (23.5°C for the CO and 21.5°C for the RE). From
1800 to 1900 JST, the wet-bulb temperature in the CO was

still 1.5–2.0°C higher than that in the RE, even though bothareas had the same dry-bulb temperature. This indicates that
the CO retained greater amounts of water vapor for longer
periods compared to the RE. The wet-bulb temperature in
the CO increased rapidly at most observation points when
the southeast sea breeze arrived. In contrast, in the RE, thewet-bulb temperature decreased until evening. This difference was caused by moist air transported from a river about
1 km upwind from the CO. The moist air forced an increasein the WBGT and elevated the risk of heat disorder in the
CO. The spatially averaged globe temperature of the CO at
1500 JST was 6.2°C lower than that at the RE, causing the
WBGT of the CO to decrease. The results suggest that thehigher WBGT in the CO was caused by higher wet-bulb
temperatures. On a day with southwest winds, the CO andRE showed no difference in WBGT because the river was
not included in the upwind source area.

Y. Ohashi (*) : T. Kawabe : Y. Shigeta
Faculty of Informatics, Okayama University of Science,
Okayama, Japane-mail: ohashi@big.ous.ac.jp

1 Introduction

Y. Hirano
Faculty of Engineering, Gunma University,
Kinyu, Japan
H. Kusaka
Center for Computational Sciences, University of Tsukuba,
Tsukuba, Japan
H. Fudeyasu
International Pacific Research Center,
University of Hawaii at Manoa,
Honolulu, Hawaii, USA
K. Fukao
Faculty of Engineering, Gifu University,
Gifu, Japan

Heat indices, such as the temperature-humidity index andeffective temperature, have been used to evaluate theclimatic comfort of urban parks (Barradas 1991; Saaroni
and Ziv 2003), livestock stress (de la Casa and Ravelo
2003; Somparn et al. 2004), and heat stress during outdoor
activities (Hoshi and Inaba 2005). In Japan, the urban heatisland phenomenon, caused by artificial land surfaces andanthropogenic heat release, has become a serious social
problem, contributing to numerous incidents of heatdisorder among urban residents in the summer season. In
urban areas, it is thus important to minimize heat disorders
by predicting local climate with heat indices. However,while heat indices are useful for predicting and avoiding therisk of heat disorder, the aforementioned heat indices

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Theor Appl Climatol (2009) 95:279–289

exclude the effect of solar radiation, which is a key factor in
urban climate. To overcome this issue, the wet-bulb globe
temperature (WBGT) includes temperature, humidity, andradiation effects, and is a popular index for predicting heatdisorders in urban environments. This index was initiallydeveloped to control heat casualties during military training(Yaglou and Minard 1957) but has since been widely used,
including in regard to sports and physical labor (e.g.,Hughson et al. 1983; Smolander et al. 1991; Hoshi andInaba 2005). Two factors contribute to the widespread useof the WBGT index: the International Organization ofStandardization recommended it as a standard in 1989 (ISO7243), and the index allows for easy estimation of the riskof heat disorder without solving heat balance equations forthe human body.
To examine living-space climate in a mid-sized city, weinvestigated the urban climate of Okayama City (population∼700,000), Japan. The WBGT index was calculated frommeteorological observations by the authors and theircolleagues in commercial and residential spaces.

2 Meteorological observations
We conducted meteorological observations from 1000 to2000 JST on September 3 (first observation), 2004, andfrom 0800 to 2000 JST on August 9 (second observation),
August 30 (third observation), and September 17 (fourth
observation), 2005, in urban commercial space consistingof multi-story office buildings and substantial humanactivities, and in suburban residential space consisting ofone- and two-story housing in Okayama City (Fig. 1). In

each type of space, we measured surface meteorologicalelements at a height of 1.5 m at eight (2004 observation) or
nine points (2005 observations). The observation points inthe commercial space extended over a 500-m square area,
while those in the residential space extended over an 800-m
square area. The observation points were chosen so as toinclude north-south streets, east-west streets, and street
crossings (Fig. 2); we traveled by bicycle to the sites andmeasured meteorological elements at each site once anhour. We also estimated the sky-view factor at eachobservation site and photographed the sky with a fish-eyelens. While the commercial space had mean sky-view
factors of 0.57 (first observation) and 0.44 (second, third,
fourth observations), the residential space had values of
0.77 and 0.70 (Table 1). Hereafter, we refer to commercial
and residential spaces as CO and RE, respectively. The
observed spaces were located approximately 16 km fromthe south coast of the Seto Inland Sea, with the RE locatedabout 2.5 km southwest of the CO.
The Okayama Meteorological Observatory is located near
the CO (the solid circle in Fig. 2a). Figure 3 shows thesunshine duration (at a height of 70.8m; i.e., above theurban canopy layer) measured by the Okayama Meteorological Observatory during the observation periods. Sunshine duration at an hour represents the value over theprevious hour; for example, the sunshine duration at 1500
JST indicates the value for 1400–1500 JST. A Pacific highpressure system covered Japan during the first and second
observation periods, creating clear, calm conditions at
Okayama City, as shown in Fig. 3. However, at 1800 JST
during the second observation, our observation was interrupted by a short rain shower. Cloudy conditions occurred

50

35

Okayama Prefecture

45

34.9

Latitude (° )

40

34.8
35

36
34.7
30

Latitude (° )Japan 35.5

25

35

20
120

125

130

135

140

Longitude (° )

34.5

145

150

Commercial space

•
34.6

•

Residential space

A

34.5

34

Latitude (° )34.4

Seto Inland Sea

33.5
34.3
133.5 133.55 133.6 133.65 133.7 133.75 133.8 133.85 133.9 133.95

33

Longitude (° )

32.5

32
132

132.5

133

133.5

134

134.5

135

135.5

136

Longitude (° )Fig. 1 Map showing the locations of the observation points in Okayama City, Japan134

134.05 134.1 134.15 134.2

Theor Appl Climatol (2009) 95:279–289

281

Fig. 2 Map of the observation points in (a) commercial (CO) and (b)residential (RE) spaces. Arabic numerals indicate the observation
points in 2004, while Roman numerals represent the observation

points in 2005. The solid circle in (a) shows the location of the
Okayama Meteorological Observatory

during the third and fourth observations, with the thirdobservation discontinued after 1400 JST because of rain.
We moved to the observation points by bicycle andmeasured the wind speed and direction, dry- and wet-bulb
temperatures, and road-surface temperature at each point.
We also checked whether the observation point was sunnyor shaded. Table 2 summarizes the measured meteorological elements. The dry- and wet-bulb temperatures and theroad-surface temperature were measured by a thermistor
thermometer. Wind speed and direction were recorded as
the mean speed and the most frequent direction within a 3min period, respectively. The meteorological elements wererecorded every 15 s; the data were then analyzed as timemean values for 3 min.

shield. We then converted the measured temperatures into
natural values as follows:

1900

1800

1700

1600

1500

1400

1300

1200

1100

1000

Obs.1stObs.2ndObs.3rdObs.4th0900

Here, Tw (°C) is the wet-bulb temperature, Tg (°C) is theglobe temperature, and Td (°C) is the dry-bulb temperature.
Normally, Td and Tw are measured under natural ventilation,with the Tw thermometer exposed to solar radiation and theTd thermometer shaded from radiation. To obtain standard,
accurate temperatures, we measured Td and Tw under forced
ventilation and placed the instrument sensors in a radiation

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0800

ð1Þ

ð3Þ

where Tdv and Twv are the forcibly ventilated and shaded
temperatures from our observations, respectively. Equations(2) and (3) were obtained from regression analysis in ourprevious research. Here, Tg in Eqs (2) and (3) were
measured by using the Belnon-type globe temperature.
Normally, Tg is measured with a globe thermometer.
However, the direct measurement of Tg is difficult for

0700

WBGT ¼ 0:7Tw þ 0:2Tg þ 0:1Td :Tw ¼ Twv þ 0:0423Tg  0:6703;

0600

The WBGT under outdoor conditions is given by thefollowing formula:

ð2Þ

and

Sunshine duration (hour)

3 Results

Td ¼ Tdv þ 0:1326Tg  3:7442

JST
Fig. 3 Sunshine duration measured at the roof level (70.8 m) of the
Okayama Meteorological Observatory

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Theor Appl Climatol (2009) 95:279–289

Table 1 Characteristics of the sky-view factor in the CO and the RE
1st Obs.

Average
S. D.
Maximum
Minimum

2nd/3rd/4th Obs.

CO

RE

CO

RE

0.57
0.12
0.76
0.41

0.77
0.08
0.84
0.60

0.44
0.15
0.67
0.24

0.70
0.08
0.76
0.51

moving observations because of the need for long-term
measurement. Accordingly, we used the estimation scheme
for Tg proposed by Tonouchi et al. (2006):
Tg ¼ Tdv þ 0:017S  0:208U ;

ð4Þ

−2

−2

where S (W m ) is the solar radiation, and U (m s ) is thewind speed. This scheme was constructed empirically fromdata including many actual observations and has been used
for predicting heat disorder risk, as discussed on thewebsite of the National Institute for Environmental Studies
of Japan (http://www.nies.go.jp/health/HeatStroke/).
The surface wind speed measured at the observation
points was used for U in Eq. (4). Since the calculation of
globe temperature required estimation of the solar radiation,
the hourly solar radiation (Sh) was calculated using thesunshine duration measured at a tower of the Okayama
Meteorological Observatory:
Sh ¼ Sh;SDh ¼0 ð1  SDh Þ þ Sh;SDh ¼1 SDh ;ð5Þ
Sh;SDh ¼0 ¼ 0:1312 þ 0:1762SDday S0 þ 0:00586;

ð6Þ

duration to the possible daily sunshine duration, and Tday isthe daily average temperature (°C). Sh,SDh = 0 and Sh,SDh = 1
represent the hourly solar radiation under cloudy and clearsky conditions, respectively. Thus, Eqs. (6) and (7) imply
that the solar radiation amounts under cloudy and sunnyconditions were averaged and weighted by the sunshine
duration. These equations were proposed by Nimiya et al.
(1997), who validated them based on data from numerous
observation stations.
The solar radiation reaching a nearby road surface had tobe estimated at each observation point. The Sh value of
insolation in the horizontal plane was divided into solar
radiation directed at and scattered onto the road:Sh ¼ Sdir þ Ssca ;ð8Þwith the directed and scattered radiation used in Eq. (8)separated as follows (Japan Meteorological Agency 1999):

Ssca¼ a0 þ a1 KT þ a2 KT2 þ a3 KT3 þ a4 KT h þ a5 h þ $M :Sh
ð9ÞIn the above equation, KT is the ratio of Sh to S0, and h is
the solar altitude (deg.). The constant values of a0, a1, a2,
a3, a4 and a5 depend on the sunshine duration, and ΔM isthe correction term for each month.
We also noted whether an observation point on the roadwas sunny or shaded. Accordingly, the solar radiation on
the road, S, was calculated as follows:
S ¼ Sdir þ Ssca SVF;

ð10Þ

if a sunny road;

and

and

Sh;SDh ¼1 ¼ 0:7696 þ 0:074SDday  0:00231Tday S0  0:2889;

ð7Þ
where SDh is the hourly sunshine duration (ranging from
0.0 to 1.0), S0 is the hourly extraterrestrial horizontal
radiation (J m−2 h−1), SDday is the ratio of the daily sunshine

S ¼ Ssca SVF;ð11Þ

if a shaded road;where SVF is the sky-view factor over the road at theobservation point. The values of S obtained by Eqs. (10)and (11) were substituted into Eq. (4) to calculate the globe
temperature.
Unfortunately, during the second observation, insolation
conditions were not noted at the observation points. As
shown in Fig. 3, the day of the second observation had clear
weather similar to that for the first observation. The
insolation conditions cannot be inferred from the results

Table 2 The meteorological elements measured in this study

Dry-bulb temperature
Wet-bulb temperature
Road-surface temperatureWind speed
Wind direction
Check of sunshine

1st Obs.
2004 September 3

2nd Obs.
2005 August 9

3rd Obs.
2005 August 30

4th Obs.
2005 September 17

○
○
○
○
○
○

○
○
×
○
○
×

○
○
×
○
○
○

○
○
○
○
○
○

Theor Appl Climatol (2009) 95:279–289

283

of the first observation because the observation points
differed. For this reason, we assumed that all observation
points were sunny until 1600 JST at the CO and 1700 JST
at the RE.
Figure 4 shows the WBGT values estimated for each CO
and RE site using Eqs. (1) to (11). In the first observation,
the CO and RE had the same spatially averaged WBGT insunny areas until 1200 JST. Then, the WBGT in the RE
gradually decreased until 1900 JST, whereas the WBGT in
the CO did not decrease substantially after 1300 JST. The
sunny WBGT in the CO was higher than that in the RE at
1500 JST and 1600 JST (P<0.01). On the other hand, theshaded WBGT at the CO was higher than that at the RE at
1700, 1800, and 1900 JST (P<0.01; two-sided T-test). The
mean WBGT for the CO was 1.4°C higher than that for the
RE at 1900 JST. At this time, the greatest difference in
the WBGT estimated at each observation point was 2.0°C(23.5°C and 21.5°C for the CO and RE, respectively).
Table 3 displays the WBGT value at each observation pointof the CO and RE during the first observation period. The
light, medium, and heavy shadings indicate “warning”,“alert”, and “severe alert” conditions, respectively, foroutdoor activities (sports or daily life). “Safe” conditions

exist below 21.0°C, “warning” conditions exist between
21.0 and 25.0°C, “alert” conditions exist between 25.0
and 28°C, “severe alert” conditions exist between 28.0 and
31.0°C, and “ban on sports” or “danger” conditions exist
over 31.0°C. These ratings have been proposed by theJapan Sports Association (JASA) and the Japanese Societyof Biometeorology (JSB). At all sunny points for both the
CO and RE, “alert” conditions appeared until 1600 JST. All
CO and RE points were shaded after 1700 JST, and “alert”
conditions were changed back to “warning” conditions.
However, the mean WBGT values of the CO began toexceed those of the RE after 1400 JST. This difference
remained even when all observation points were shaded(1800–1900 JST).
In the second observation, the mean WBGT exceeded
27°C, corresponding to “alert” conditions. After 1000 JST,
“severe alert” conditions appeared, followed by “ban on
sports” or “danger” conditions beginning to appear around1100 JST. There was little difference in the mean WBGT
between the CO and RE during the second observation
period (except for between 0900 and 1000 JST when data
were missing for the CO). In the third observation, themean WBGT was between 25 and 26°C until a rain shower(a) 1st Observation(b) 2nd Observation

29.0

RE (sunny)
P < 0.01

CO (shade)

WBGT (°C)

27.0

RE (shade)

P < 0.01

26.0
25.0

P < 0.01

24.0

P < 0.01

23.0

WBGT (°C)

28.0

CO (sunny)

P < 0.01

22.0
21.01100 1200 1300 1400 1500 1600 1700 1800 1900

CO (sunny)
34.0
RE (sunny)
33.0
CO (shade)
32.0
RE (shade)
31.0
30.0
29.0
28.0
27.0
26.0
25.0
24.0
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900

JST

JST
27.0

(c) 3rd Observation

26.0

CO (shade)
RE (shade)

WBGT (°C)

25.0

CO (sunny)
RE (sunny)
CO (shade)

25.0

26.0

WBGT (°C)(d) 4th Observation

RE (shade)

24.0
P < 0.01
P < 0.01

24.0

23.0

23.0

22.0

P < 0.01
P < 0.01

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900

900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900

JST

JST

Fig. 4 Temporal variation of the spatially averaged WBGT estimated from observations at the CO and RE sites. The solid and dashed lines
indicate the results for the CO and RE, respectively. The light and heavy lines represent sunny and shaded points, respectively

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Theor Appl Climatol (2009) 95:279–289

Table 3 WBGT calculated at each point in the (a) CO and (b) RE during first observation period(a) Commercial space(b) Residential space
Sunny Shade
Ave.
Ave.

1

2

3

4

5

6

7

8

27.6

26.4

26.6

26.0

26.3

26.6

25.8

27.4

26.6

1100JST

1200JST 28.3

27.4

27.7

27.0

27.6

27.5

27.9

28.2

27.7

1300JST 28.2

27.3

27.0

26.8

26.8

26.8

24.5

27.7

27.2

1400JST 25.6

27.6

27.6

27.2

27.6

27.0

24.2

27.3

1500JST 25.2

23.7

24.9

26.6

27.4

27.2

24.4

1600JST 24.4

24.1

25.0

25.5

26.3

26.1

1700JST 24.7

23.9

23.9

23.8

24.5

1800JST 23.3

23.5

23.6

23.7

1900JST 23.5

23.3

23.2

23.4

1100JST

Sunny Shade
Ave. Ave.

1

2

3

4

5

6

7

8

26.0

27.0

26.3

26.7

26.7

27.2

27.2

26.6

26.7

1200JST 27.2

28.2

27.9

28.0

28.3

27.4

27.9

27.7

27.8

24.5

1300JST 27.6

28.2

27.2

27.8

28.2

27.9

26.6

27.5

27.6

27.4

24.9

1400JST 27.3

27.6

26.2

26.6

27.1

27.6

×

27.7

27.2

26.8

27.0

24.5

1500JST 26.4

26.6

26.1

26.3

26.7

27.0

26.7

26.6

26.6

24.8

24.3

25.9

24.5

1600JST 24.8

26.0

25.0

25.3

24.9

25.4

25.5

25.6

25.3

24.2

23.7

24.1

24.1

1700JST 22.7

23.9

23.2

23.8

23.9

23.9

23.0

23.3

23.6

23.5

23.1

22.5

23.1

23.3

1800JST 22.3

21.9

21.7

22.5

22.6

22.7

22.1

22.4

22.3

23.2

23.1

23.0

23.3

23.3

1900JST 22.0

21.5

21.5

22.0

22.0

22.7

21.7

21.9

21.9

23.5

Heavy, medium, light, and no shading indicate “severe alert”, “alert”, “warning”, and “safe” conditions for outdoor activities, respectively, basedon guidelines from the Japan Sports Association and Japanese Society of Biometeorology

led to a discontinuance of observations. The mean WBGT
values for the CO and RE were almost the same in the thirdobservation. Because of cloudy conditions for the entire
day, conditions fell between “warning” and “alert.” In the
fourth observation, cloudy conditions produced some shadein both the CO and RE. Consequently, “warning” conditions occurred during the entire day. The mean WBGT in
the RE was higher than that in the CO especially until 1200
JST (P<0.01).
Table 4 shows the spatially and temporally averaged
values of all meteorological elements measured in the CO

and RE. In the afternoon of the first observation, WBGT
values in the CO were higher than those in the RE. The
spatially averaged air temperatures in the CO, however,were 1°C lower than those in the RE between 1300 and
1600 JST. As shown in Fig. 5, the globe temperature
calculated in the CO was lower than that in the RE.
Therefore, the high WBGT in the CO was induced by thehigh specific humidity (water-vapor contents) in that space.
Figure 5 also reveals that the wet-bulb temperature in the
CO was 1°C higher than that in the RE after 1400 JST. In
the second observation, the globe temperature differed little

Table 4 Mean values of the meteorological elements measured in the CO and the RE. Except for “hours of sun (shade),” the values inparentheses indicate the standard deviation of the mean

1st Obs.
2nd Obs. (Lack ofdata in 1800 JST
and 1000–1100 JST
in CO)
3rd Obs. (Lack of datain 1400–1900 JST)
4th Obs.

Typeof area

Mean airtemperature(°C)

Mean roadtemperature(°C)

Mean specifichumidity (g kg−1)

Mean windspeed (m s−1)

Mean winddirection

Hours of sunny(shade)

CO
RE
CO
RE

29.1 (0.6)
29.7 (0.7)
33.8 (0.5)
33.0 (0.6)

38.2 (3.2)
40.5 (2.2)
No data
No data

12.5 (0.7)
10.9 (0.3)
17.1 (0.2)
17.6 (0.2)

1.0 (0.8)
1.0 (0.4)
0.4 (0.5)
0.3 (0.3)

SE-S-SW LARGE
E-SE-S
S-SW LARGE
S-SW

42 (46)58 (30)No data
No data

CO
RE
CO
RE

27.8 (0.3)
27.5 (0.2)
27.4 (0.3)
27.3 (0.3)

No data
No data
32.2 (2.3)
35.6 (1.2)

22.8 (0.1)
22.5 (0.2)
12.3 (0.1)
12.5 (0.1)

0.4 (0.2)
0.3 (0.2)
0.4 (0.2)
0.3 (0.4)

SE-S-SW
Not specified
SE-S-SW LARGE
SE-S

4 (41)
8 (37)
21 (87)24 (84)

Theor Appl Climatol (2009) 95:279–289

(a)

1
0.5

1900

1800

1700

1600

1500

1400

1300

1200

1100

-0.5

1000

0
0900

Dry-bulb temperature
difference (°C)

1.5

285

JST

-1
-1.5
-2

Obs.1stObs.2ndObs.3rdcontrast, the globe temperature calculated for the CO waslower than that for the RE, which resulted in the CO andRE having the same WBGT. In the fourth observation, alltemperatures in the CO were lower than those in the RE
during the morning. As a result, the spatially averaged
WBGT in the CO was 0.8°C lower than that in the RE from
1000–1100 JST (P<0.01). In the following section, we
discuss how the meteorological elements and the WBGT
values differed between the CO and RE on each observation day.

Obs.4th

4 Discussion
Obs.1stWet-bulb temperature
difference (°C)

2
1.5

Obs.2ndObs.3rdObs.4th

(b)

1
0.5
0

Figure 6 shows the relationship between the sky-view
factor and the road surface temperature (Fig. 6a), WBGT
(Fig. 6b), which are averaged for the observation period.
The road temperature in the CO correlated positively withthe sky-view factor. Also, the road temperatures in the CO
were entirely lower than those in the RE. These mean thesolar radiation insolates sufficiently onto the road surfaces
in the RE. However, the WBGTs in the CO became to bealmost higher than those in the RE. This result suggests that

1900

1800

1700

Obs.3rdObs.4th

1

-3

1900

1800

1700

1600

1500

1400

1300

1200

-2

1100

-1

1000

0

JST

Temporally Averaged Road
Temperature (°C)

Obs.2nd

1600

1500

1400

1300

1200

Obs.1st

0900

42.0
41.0
40.0
39.0
38.0
37.0
36.0
35.0
34.0
33.0
32.0

-4
-5
-6

(a)
r = 0.08

r = 0.37

CORE

1st Obs.
0

(c)

-7

Fig. 5 Temporal variation of spatially averaged (a) dry-bulb
temperature differences, (b) wet-bulb temperature differences, and(c) globe temperature differences between the CO and RE (CO minusRE)between the CO and RE (Fig. 5c). Although the spatiallyand temporally averaged air temperature (dry-bulb temperature) in the CO was higher than that in the RE, the WBGT
value in the CO was almost the same as that in the RE; thereason is that the specific humidity (wet-bulb temperature)in the CO was lower than that in the RE, as shown in
Table 4 and Fig. 5.
During the third observation, both dry- and wet-bulb
temperatures in the CO were higher than those in the RE. In

0.2

0.4

0.6

0.8

1

Sky-View Factor (–)

Temporally Averaged WBGT (°C)

Globe temperature difference
(°C )

2

1100

1000

0900

JST
-0.5

26

(b)

r = 0.55

25.6
r= 0.70

25.2

24.8

CO
RE

st

1 Obs.
24.4
0

0.2

0.4

0.6

0.8

1

Sky-View Factor (–)
Fig. 6 Scatter diagrams of the sky-view factor and the (a) temporally
averaged road surface temperature, (b) temporally averaged WBGT, in
the first observation. The value of symbol r represents the correlation
coefficient286

Theor Appl Climatol (2009) 95:279–289

Table 5 Parameter values used in Eqs. (12) and (13) for calculation of the source area (from Schmid 1994)
Parametersaexm

StableUnstable
StableUnstable
StableUnstable

Equation

α1

α2

α3

α4

(12)
(12)
(12)
(13)
(12)
(13)

0.773
0.853
30.4
40.4
4.30
5.37

1.24
1.23
1.23
1.22
1.28
1.25

0.957
0.441
2.60
15.5
1.74
5.96

1.25
1.00
0.452
−0.5480.688−0.472the WBGT does not depend only on the radiation
environment locally at the point. Within a day, meteorological fields are affected not only by the microscale
environment but also by the upwind environment. Thus,
Fig. 7 Regions including thesource area aligned from the
upwind edge to the downwindedge for each site under (a)unstable and (b) stable conditions in the CO (z0=1.0 m) andRE (z0=0.2 m). Solid lines represent areas connecting theedges of the source-area lengthfor z/L=0.1 in (a) and -z/L=
4.0×10−4 in (b). Dashed lines
represent those connecting the
upward edges of source areas
for z/L=2.0×10−4 in (a) and-z/L=1 in (b)we consider upwind areas that influenced the backgroundmeteorological fields of the observation points.
Schmid (1994) estimated the “source area” for passive
scalars that influence observation data using a backward(a) Unstable conditions
CO

2nd Obs.

RE

1st Obs.

1st Obs.

2nd Obs.

Asahigawa River(b) Stable conditionsCO
3rd , 4th Obs.
RE
3rd , 4th Obs.

Asahigawa River

Theor Appl Climatol (2009) 95:279–289

287

trajectory that considered the effects of turbulent diffusion.
The parameters D1 and D2 of the source area vary withatmospheric stability: a2
  z a 4 z
D 1 ¼ z0 a 1
exp a3
ð12Þ
z0
L
and
D 2 ¼ z0 a 1

 a2 zz a4
1  a3
;
z0
L

ð13Þ

where z0 is the roughness length, and L is the MoninObukhov stability length. Table 5 lists the values of α1, α2,
α3, and α4. Although z represents the actual observation
height, we regarded this height as the sea-breeze heightover the CO canopy layer (i.e., z=30m). In Eq. (12), D1
corresponds to a (m) under stable and unstable conditions
and to e (m) and xm (m) under stable conditions, where a isthe distance from the upwind edge of the source area to an
observation point, e is the distance from the downwindedge of the source area to an observation point, and xm isthe maximum source location from an observation point.
On the other hand, e and xm under unstable conditions arecalculated using Eq. (13) (i.e., D2 is e and xm). Here, we
assume z0 values of 1.0 and 0.2 m, respectively, for the CO
and RE. The calculation results for the source area aresummarized in Fig. 7 and Table 6.
The Pasquill stability classes (Pasquill 1961) when a sea
breeze arrived at the CO and RE were estimated at location
A (the Air Quality Monitoring System of Okayama
Prefecture) shown in Fig. 1. The classes were determinedby the shortwave radiation and wind speed measured at thattime. When sea breezes covered location A, the Pasquill
stability class was B or C, implying unstable or weak
unstable conditions, respectively. This result reveals that

Table 6 Calculation results forthe source-area parameters.
The upper figure shows thelocations of the source-areaparameters

unstable conditions still occur in the sea-breeze stage
because of surface heating by solar radiation. That is, thefirst and second observations were under unstable conditions during the daytime. Consequently, a=35–56 (52–81) m, e=551–2553 (785–3637) m, and xm =150–376(226–563) m are valid for the CO (RE) from thecalculations of Eqs. (12) and (13). In Fig. 7a, the valuesof e (i.e., the source area length parallel to the winddirection) were drawn according to the prominent winddirection of sea breezes, including the southeast andsouthwest sea breezes (data measured at the Okayama
Meteorological Observatory) during the first and second
observations, respectively. During the first observation, thesource area of the CO included a nearby “Class A” greatriver (the Asahigawa River), while that of the RE included
an area of many residential houses but not the river.
Therefore, the southeast sea breeze tends to transport moist
air supplied from the river into the CO, leading to higher
wet-bulb temperatures in the CO than in the RE (Fig. 5b).
As shown in Eq. (1), the wet-bulb temperature strongly
affects the WBGT value (70%), whereas the dry-bulb
temperature is not so important for the WBGT (10%). Thus,
the WBGT in the CO exceeded that in the RE during thesouthern sea-breeze stage, despite the lower globe temperature of the CO.
In contrast, in the second observation, the higher drybulb temperature and slightly lower wet-bulb temperature
measured in the CO probably resulted from the transport ofwarm, dry air from the many office buildings and heavy
traffic within the upwind source area. However, thesefeatures had little effect on the WBGT difference between
the CO and the RE.
The third and fourth observations were made understable conditions created by clouds. Therefore, a=52–55

wind
a

d

xm
e

Observation
point

Source areaCOz/L

-1 -4 10-4
(unstable)

a (m)

RE
10-4 0.1(stable)-1 -4 10-4
(unstable)

2 10-4 0.1(stable)

36 56

52 55

52 81

77 81

xm (m)

151 377

336 478

226 563527 749e (m)551 2,553

2,107 4,995

785 3,637

3,052 7,233

2

288

Theor Appl Climatol (2009) 95:279–289(77–81) m, e=2107–4495 (3052–7233) m, and xm =336–
478 (527–749) m were estimated for the CO (RE) as shownin Table 6. During daytime, the east wind was prominent inboth the third and fourth observations. In addition, understable conditions, the source area extended further downwind compared with the source area for the unstableconditions in the first and second observations. As shownin Fig. 7b, the source areas in both the CO and RE included
not only the river, but also quasi-homogeneous land-use
surfaces (mainly rice paddies, fields, and forests). As aresult, there was little difference in dry- and wet-bulb
temperatures between the CO and RE.

breezes. This result is attributable to the similarity of the
upwind sources areas for the CO and RE.
The above results demonstrate that the daily biometeorological environment in the study area is determined by
not only radiation and microscale meteorological conditions
but also by mesoscale flow conditions, as defined by thesource area. Therefore, assessments of human discomfort
within living spaces should include both the microscalebiometeorological environment and overlying mesoscalemeteorological conditions.
In the future, we will simulate the urban bioclimatecharacterized in this study using a mesoscale meteorological model coupled with an urban canopy model (e.g.,
Kusaka et al. 2001; Kondo et al. 2005; Ohashi et al. 2007).

5 Conclusions
We estimated the wet-bulb globe temperature (WBGT)
using measured meteorological elements to understand thebioclimates of human living spaces during summer. Our
research focused on commercial and residential spaces in
Okayama City (population of ∼700,000), Japan. The
commercial spaces (CO) mainly consisted of multi-story
office buildings, while the residential spaces (RE) consistedof one- or two-story residential buildings. The results arebriefly summarized as follows.
–

Under conditions of sunny days and southeast sea
breezes:

The WBGT value in the CO was higher than that in the
RE despite lower dry-bulb and globe temperatures in theCO; the difference appeared from 1300 JST only in sunny
locations, and after 1700 JST in shaded locations. This
relationship was caused by higher wet-bulb temperatures in
the CO created by the sea-breeze transport of moist air
originating from a river; because of the difference inupwind source areas, only the CO was affected by the
moist river air, which was the main reason for the increased
WBGT value and the enhanced the risk of heat disorders
until evening in the CO.
–

Under conditions of sunny days and southwest sea
breezes:

The CO and RE had almost the same WBGT values.
Although the dry-bulb temperature in the CO exceeded thatin the RE, the wet-bulb temperature in the CO was lower
than that in the RE because there were many buildings in
the upwind source area. While warm air increased the
WBGT, dry air decreased the WBGT in the CO. Consequently, WBGT values were similar in the CO and RE.
–

Under conditions of cloudy days with east winds:

The WBGTs in the CO and RE were almost the sameand similar to the results for sunny days with southwest sea

Acknowledgements The meteorological data were provided by theJapan Meteorological Agency, Okayama Prefecture, and relevant
cities.

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