[Original]
Evaluation of output of abnormal weather and heat island phenomenon
Yosuke HORIE1, Masahide AIKAWA2
1

Atmospheric Environmental Division, Hyogo Prefectural Institute of Environmental Sciences,3-1-27 Yukihira-cho, Suma-ku, Kobe, Hyogo, 654-0037 Japan

2

Center for Global Environmental Research, National Institute for Environmental Studies ,16-2 Onogawa, Tsukuba, Ibaraki, 305-8506 Japan

2006 年度の暖冬とヒートアイランド現象の解析
堀江

1

2

洋佑 1,

藍川

昌秀 2

兵庫県環境研究センター 大気環境科（〒654-0037 神戸市須磨区行平町 3-1-27），

国立環境研究所

地球環境研究センター（〒305-8506

茨城県つくば市小野川 16-2）

As part of a heat island survey campaign, we have been continuously monitoring the air temperature in an urban
area of approximately 10 x 15 km in Hyogo Prefecture, Japan. We analyzed the data sets of the air temperature
obtained in the above campaign from the viewpoint of the spatial distribution of the air temperature and theinfluence of abnormal weather. The air temperature in December 2006 was 2.8 C higher than that in December
2005. The winter from December 2006 through February 2007 was unusually warm. The temperature difference (2.8
C) between December 2005 and 2006 was attributed to the abnormal winter of 2006, since the 2.8 C deviation was
too large to be attributed to the progression of the heat island phenomenon in one year; further its deviation waswithin the range of the variation observed in the survey results by the Meteorological Agency of Japan around thestudy area. The abnormal winter of 2006 produced higher air temperatures in the early morning, which was the mostsignificant difference with the winter of 2005. This study newly indicates that the abnormal weather or the unusuallywarm winter of 2006 in Japan appeared in the daily-lowest air temperature, a phenomenon that generally occurs as aresult of a heat island phenomenon.

Keywords: Urban heat island, Air temperature, Spatial distribution, Annual variation, Daily-lowest air temperature,
Abnormal weather
haveI

studied

the

urban

heat

islandphenomenon 1-7). Because urban heat islands are a

INTRODUCTION

local environmental pollution issue and not a
global one, local governments must counteract

With

the

objectiveoflimiting

thermalthem. The

pollution in urban areas, scientists worldwide

6

government of Hyogo

Prefectureimplemented measures against heat islands inAugust 2005. The air temperature must be

II

METHODSmeasured to verify the effects of action plans andto establish effective measures in the future.
Aikawa et

al.8)

1.

Air temperature measurement

studied the accumulated air

The air temperature was measured at elementarytemperature data in a 15 x 15-km urban area inand junior high schools located within a 10 x 15-km

Hyogo Prefecture, Japan, and characterized thearea in Hyogo Prefecture, Japan. The geographic

growing heat island phenomenon in the area. In

characteristics and the land use of the study area are

addition,thedescribed in detail elsewhere 7). The locations of thecharacteristic air temperature distributions bysites are shown in Fig. 1. The air temperature wasseason in the relevant area using the data setsmeasured by a thermometer calibrated with aobtained

newly

thermostat bath and installed in a naturally ventilated

Hyogo

thermometer shelter positioned about 1.5 m above thePrefecture. To precisely verify the effect of theground. The data measured on the hour, i.e., hourly

actiondata, was used for the evaluation.

Aikawafromconstructed

a

by

plans

et

al. 7)

monitoring
the

and

to

clarified

network

government
proposeofeffective

andappropriate measures in the future, detailed data
sets on the air temperature must be continuously

2.

Analyzed periodcollected and properly analyzed. The data sets

In general, December, January, and February are

obtained in 2005 were previously studied inconsidered to be the winter season in Japan. Aikawa etdetail 7), and the annual variation in the summeral.7) studied in detail the characteristic air temperatureseason was also studied (unpublished). In the

distributions observed in summer and winter in urban

present study, accumulated winter data sets fromareas of Japan; in the study, they used the data sets of2005 to 2007 were analyzed, and the findings are

August and December as the representative periods ofreported in this paper.

thesummerandwinterseasons,

respectively.

Therefore, in the present study, the air temperatures
obtained in December of 2005 and 2006 wereanalyzed as the representative periods of the 2005 and2006 winter seasons.
3.

Number of survey sites
The air temperature was measured at 18 survey

sites. However, the data was missing from one surveysite in December 2005 and from two sites in
December 2006, as a result of which 17 datasets for
December 2006 and 16 for December 2005 wereavailable. To compare the monthly air temperature
distributions in December of 2005 and 2006, the data
sets obtained at 15 survey sites, excluding the above 3(1+2) survey sites, were used.
4.

Altitude correction
The air temperatures were corrected by the altitudeof the sites and a temperature-lapse rate of 0.6 C /100
m when the air temperatures of the sites werecompared. The temperature-lapse rate should varydepending on the season and the time (daytime andFig. 1

Location map of the survey site.

7

nighttime). Therefore, it is difficult to reflect thep = monthly mean air temperature, monthly mean ofvariation of the temperature-lapse rate precisely. On

the daily highest air temperatures, monthly mean of

the other hand, fog is frequently observed at Mt.

the daily lowest air temperatures), Tip

Rokko (summit: 931 m a.s.l), which is located next totemperature at site i and for p, and T’p

the present study area

9-12)

. Aikawa et al.

7,13)is the airis theaverage of Tip for each p.

applied 0.6 C /100 m for the correction of the air

The distribution patterns in December 2005 andtemperature in the previous study. Therefore, we

2006 were similar, i.e., the air temperature in theemployed 0.6 C / 100 m in the present study,

north was lower than that in the south, although thealthough the fog is frequently observed in the summer.

pattern of 2006 was slightly different from that of2005 in the detailed distribution of the south. The

III

RESULTS AND DISCUSSION

2005 and 2006 distribution patterns of the deviation in
the monthly mean air temperature (Figs. 3 (a)-1 and1.

Peculiarities of the 2006 winter(b)-1), monthly mean of the daily highest air

Figs. 2 shows the trends of the monthly mean air

temperatures (Figs. 3 (a)-2 and (b)-2), and monthly

temperatures in December, January, and February,mean of the daily lowest air temperatures (Figs. 3

observed at the Kobe Marine Observatory. The 2006(a)-3 and (b)-3) were similar in each year. Therefore,

winter (December 2006 through February 2007)

the following analysis and discussion are based on theproved to be unusually warm. This peculiarity of thedata sets of the monthly mean air temperatures.

2006 winter was most typically observed in January
and February 2007.

4.

Difference in air temperature between Decemberof 2005 and 2006
2.

Comparison

of

the

monthlymean

airFig. 4 shows the distribution of the difference in thetemperatures

air temperature between December 2005 and 2006,

The monthly mean air temperature, not being

where the difference is defined as  = air temperaturecorrected by the altitude, is summarized in Table 1.

in December 2006 – air temperature in December

The monthly mean air temperature in December 2006

2005. In Fig. 4, the difference in the air temperature

was 2.8 C higher than that in December 2005. The

seems to be large at survey sites located in the north.

median values of the air temperature among the

In the present survey area, the altitude is higher in thesurvey sites in December of 2005 and 2006 were 6.0

north than in the south 7), showing that the higher

and 8.5 C, respectively, showing that the air

altitude likely resulted in the larger difference in thetemperature in December 2006 was higher than that in

air temperature. On the other hand, in the present

December 2005.

survey area, the survey site with the higher altitude is
generally located in an area far from the coast,

Table 1 Monthly mean air temperatures in Decembers 2005 and 2006
Unit: oC
2005
2006
Monthly mean air temperature

5.7

indicating that distance from the nearest coast mightalso be responsible for the variation in the air

8.5

temperature between December 2005 and 2006.

Note: The air temperatures are not corrected by the altitude.

Fig. 5(a) and (b) shows the relationship between thealtitude of the survey site (a), the distance from the3.

Distribution of the deviation in the monthly air

nearest coast to the survey site (b), and the difference

temperaturesin the air temperature between December 2005 andThe distribution of the deviation for the monthly

2006. In the relationship between the altitude and themean air temperature, monthly mean of the daily

difference (Fig. 5(a)), when the altitude of the survey

highest air temperatures, and monthly mean of thesite was higher than 20 m, the difference in the air

daily lowest air temperatures in December of 2005

temperature had a clearly linear relationship with theand 2006 are shown in Figs. 3(a) and (b), respectively,

altitude, and the higher altitude provided a larger

where the deviation is defined as Tip – T’p(i = site,

difference in the air temperature between December
82005 and 2006. In contrast, there was no relationshipFig. 6(b) indicates that the air temperatures in the

between the distance from the nearest coast to theearly morning (4:00 – 8:00) and during the daytime

survey site and the difference in the air temperature(8:00 – 18:00) made a larger contribution to thebetween December 2005 and 2006 (Fig. 5(b)). Aikawa

difference in the air temperature between December

et al.

7)demonstrated that the current survey area can2005 and 2006. In particular, the contribution in the

be classified into three categories: (1) the highly

early morning was large at most sites.

urbanized area along the coast, (2) the suburban area,
primarily in the southern part of the study area, and6.

Evaluation of the influence of an unusually warm(3) the residential area being developed as satellite

wintercities, primarily in the northern part of the study area.

In general, the daily lowest air temperature was7)

According to the classification by Aikawa et al. ,observed in the early morning in the diurnal variation,

there would be no or little change of the land use

and, in fact, the daily lowest air temperature waspattern in the southern part, while the residential

noted at 8:00 at all sites in the present study. As

development possibly progressed in the northern part.

shown in Fig. 6(b), the largest contribution to the

When quantitatively considering the surface conditiondifference in the air temperature between December

around the survey area, Britter and Hanna

14)

studied2005 and 2006 was observed in the early morning, or,the surface roughness length of the urban area byin other words, the influence of the warm winter of

introducing “lambda parameter”; and further, Klysik

2006 was the clearest in the difference in the earlyand Fortuniak 15) studied the degree of the obstruction

morning. On the other hand, larger increasing trendsof the horizon around the survey site. However, wefor the daily lowest air temperature were reported as

can not calculate the change of the land use patternrelated to the phenomenon of urban heat islands 16-19).

between 2005 and 2006 because the land use data

In the present study, the air temperature in December

prepared in 1997 by the National Land Agency of2006 was 2.8 C higher than that in December 2006,

Japan is the latest. On the other hand, the change ofas described in 3.2. The mean difference in the air

the land use pattern would not be so drastic becausetemperature between December 2005 and 2006

the passage of time is just one year.

observed in the survey by the Meteorological Agencyof Japan around the present survey area was 3.5 C

5. Temporal dependence of the difference in air(the number of the site: 20); maximum and minimum

temperature between December 2005 and 2006

was 4.2 C and 2.6 C, respectively. The variation of

The temporal dependence of the difference in the

2.8 C was within the range of the variation observed

air temperature between December 2005 and 2006 isin the results by the Meteorological Agency of Japan.

shown in Fig. 6(a). Fig. 6(a) indicates that the air

The survey sites of the Meteorological Agency oftemperatures in December 2006 were higher at any

Japan were distributed in the rural and remote areas asgiven time than those in December 2005. On the otherwell as in the urban area. Therefore, the variation ofhand, the difference seems to show a temporal

2.8 C in our present study should be mainly

dependence in that the difference was larger in theattributed to the deviation due to global phenomena,

early morning (4:00 – 8:00) than at any other time.

such as abnormal weather, rather than local causes,

Fig. 6(b) also shows the difference in the airsuch as the progression of the heat island phenomenon.

temperature between December 2005 and 2006, where

The influence of the heat island phenomenon is

the following value is plotted along the vertical axis:

clearlytemperature

The value of the vertical axis = it - iobserved(i = site, t =16-19)

in

the

daily

lowestair. Accordingly, the present study

newly indicates that global phenomena, such as

0:00 to 23:00), where it is the difference in the air

abnormal weather, may influence changes in the daily

temperature between December 2005 and 2006 at site

lowest air temperature along with heat islandi and at time t, and iphenomena.

is the average of it at site i.
92006 data

December(2006 winter season)

o

C

9

/

6

2005 data

3(2005 winter season)
2007

1997

1987

1977

1967

1957

1947

1937

1927

1917

1907

0
1897

Mean air temperature in December

12

12January
2007 data

9(2006 winter season)

C
/

o

6

2006 data

3(2005 winter season)
2007

1997

1987

1977

1967

1957

1947

1937

1927

1917

1907

0
1897

Mean air temperature in January

Year

12

February

2007 data

9(2006 winter season)

C

6

2006 data(2005 winter season)

3

2007

1997

1987

1977

1967

1957

1947

1937

1927

1917

1907

0
1897

/

o

Mean air temperature in February

Year

Year

Fig. 2

Trend of the monthly mean air temperature in December, January and February.

The data was observed in the Kobe Marine Observatory.

10

(a)-1

(a)-2

(a)-3

(b)-1

(b)-2

(b)-3

Fig. 3 (a)-1: Distribution of the deviation in the monthly mean air temperatures in December 2005.
(a)-2: Distribution of the deviation in the monthly mean of the daily-highest air temperatures in December 2005.
(a)-3: Distribution of the deviation in the monthly mean of the daily-lowest air temperatures in December 2005.
(b)-1: Distribution of the deviation in the monthly mean air temperatures in December 2006.
(b)-2: Distribution of the deviation in the monthly mean of the daily-highest air temperatures in December 2006.
(b)-3: Distribution of the deviation in the monthly mean of the daily-lowest air temperatures in December 2006.

11

Fig. 4

Distribution of the difference of the airtemperature between Decembers 2005 and 2006

Variation of air temperature[=2006.12-2005.12] / oC

5(a)Fig. 6

4

Temporal dependence of the difference of the
air temperature between Decembers 20053

and 2006

Fig. 6

Temporal dependence of the difference
2of the air temperature between
Decembers 2005 and 20061(a): Vertical axis: Difference itself in air
0temperature between December
0
50
100
150
200
250
2005 and 2006
Altitude /m(a): Vertical axis: Difference itself in air temperature
between December 2005 and 2006
(b): Vertical axis: Value = it - ito 23:00)

it ; Difference in air temperature between(b): Vertical axis: Value = it - (b)(i =iDecember 2005 and 2006 at site i and at

site, t = 0:00 to 23:00)
4it ; Difference in air
temperature3
between December
22005 and 2006 at
site i and at time t,
1time t,[=2006.12-2005.12] / oC

Variation of air temperature5i ; Average of it at site i

i ; Average of it at

0
0

5

10

site i15

20

Distance to the nearest coast /km
Fig. 5(i = site, t = 0:00

Relationship between the altitude of the surveysite (a), the distance from the nearest coast to the surveysite (b) and the difference of the air temperature between
Decembers 2005 and 2006

12

Atmospheric Environment, 27B: 121-128.

IV

CONCLUSIONS

4)

Saitoh TS, Shimada T, Hoshi H, 1996. Modelingand simulation of the Tokyo urban heat island.

The data sets for the air temperature in December

Atmospheric Environment, 30: 3431-3442.

2005 and 2006 obtained from a survey network that5)

Yamashita S, 1996. Detailed structure of heatcovered a 10 x 15-km urban area in Hyogo Prefecture,island phenomena from moving observations

Japan were studied from the viewpoint of comparing

from electric tram-cars in metropolitan Tokyo.

the spatial distributions and influences of an unusual

Atmospheric Environment, 30: 429-435.

warm winter. The findings are summarized as follows.

6)

Oke TR, Spronken-Smith RA, Jauregui E,
Grimmond CSB, 1999. The energy balance of(1)The monthly mean air temperature in December

central Mexico City during the dry season.

2006 was 2.8 C higher than that in December 2005 in

Atmospheric Environment, 33: 3919-3930.

our survey network.

7)(2)The higher air temperature

was presumably

Aikawa M, Hiraki T, Eiho J, Miyazaki H, 2007a.
Characteristic

airtemperature

distributions

attributed to the deviation due to abnormal weather

observed in summer and winter in urban area inrather than to the progression of the heat island

Japan.

phenomenon in just one year.

Asseessment, 131: 255-265.

(3)The spatial distribution of the deviation in the8)

Environmental

Monitoringand

Aikawa M, Hiraki T, Sumitomo S, Eiho J, 2006.

monthly mean air temperature, monthly mean of theDistribution and Variation of the Air Temperature

daily highest air temperatures, and monthly mean offrom 1990 through 2003 in Urban Areas ofthe daily lowest air temperatures showed similar

Hyogo Prefecture from the aspect of Heat Island

patterns in each year.

Phenomenon. Bulletin of the Hyogo Prefectural(4)The influence of the warm winter was clearlyInstitute of Public Health and Environmental

observed at survey sites at higher altitudes.

Sciences, 2: 1-9.

(5)The influence of global phenomena, such as

9)

Aikawa M, Hiraki T, Shoga M, Tamaki M, 2001.

abnormal weather, was observed in the daily lowest

Fog and precipitation chemistry at Mt. Rokko in

air temperature; in other words, the influence of both

Kobe, April 1997-March 1998. Water, Air andthe heat island phenomenon and the abnormal weather

Soil Pollution, 130: 1517-1522.

was observed in the daily lowest air temperature.

10) Aikawa M, Hiraki T, Shoga M, Tamaki M, 2005a.
Chemistry of fog water collected in the Mt.

ACKNOWLEDGEMENTS

Rokko area (Kobe city, Japan) between April
1997 and March 2001. Water, Air and Soil

The authors are grateful to Professor Dr. Masakazu

Pollution, 160: 373-393.

Moriyama of Setsunan University and Dr. Hideki11) Aikawa M, Hiraki T, Shoga M, Tamaki M, 2005b.

Takebayashi of Kobe University for his support with

Six-year trend and frequency distribution of thethe calibration of the thermometer.

pH value of fog water collected on Mt. Rokko(Kobe City, Japan). Bulletin of the Hyogo

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要約2005 年度と 2006 年度の冬期（12 月から 2 月）の気温を比較すると，2006 年度の冬期は 2005 年度の冬期と比べて 2.8℃高かった．これはヒート
アイランド現象が 1 年間でより顕著になったとして解釈できる気温差ではなく，この 2.8℃の気温差は 2006 年度の冬期が暖冬（異常気象）であったためであると考えられる．2005 年度と 2006 年度の冬期を比べると，最も顕著な気温差は早朝の気温差に観測された．一般にヒートアイランド現象の影響は早朝気温（日最低気温）に，より顕著に現れるとの研究報告があるが，暖冬等の異常気象
14