Changes in Temperatures in Okayama Area Compared with Different Urbanization Areas, Japan

doi:10.4236/jep.2011.22018

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Journal of Environmental Protection, 2011, 2, 162-167

doi:10.4236/jep.2011.22018 Published Online April 2011 (http://www.SciRP.org/journal/jep)

Changes in Temperatures in Okayama Area

Compared with Different Urbanization Areas,

Japan

Noriko Sakano1*, Nobuyuki Miyatake1, Shoko Murakami1, Takeshi Suzue2, Tomohiro Hirao2, Keiki

Ogino3

1Department of Hygiene, Faculty of Medicine, Kagawa University, Kagawa, Japan; 2Department of Public Health, Faculty of

Medicine, Kagawa University, Kagawa, Japan; 3Department of Public Health, Okayama University Graduate School of Medicine,

Dentistry and Pharmaceutical Sciences, Okayama, Japan.

Email: [email protected]

Received November 11th, 2010; revised January 10th, 2011; accepted March 1st, 2011.

ABSTRACT

To investigate the changes in temperatures in Okayama area compared with different levels of three urbanization areas

such as Tsuyama, Tokyo areas and Hachijo island in Japan. Data of temperatures in Okayama (1891-2009), Tsuyama

(1943-2009), Tokyo areas (1876-2009) and Hachijo Island (1907-2009) in Japan was obtained from Japan

Meteorological Agency. Changes in temperatures in 4 areas in Japan were analyzed and compared. By using data from

1943 to 2009, some parameters of temperatures were significantly correla ted with years. The change in parameters of

temperatur es in Hachijo Island was calmest among 4 areas. The changes in mean temperature in Augu st and in a year

in Okayama area for 50 years were the highest (August: 1.55˚C, Year: 2.05˚C) among 4 areas. In addition, correlation

coefficient rate between years and the number of days over 35˚C in August in Okayama area was highest (r = 0.407, p

= 0.0037). Parameters of temperatures were gradually increased with years in Okayama area, especially in recent

years. However, those associations were not clearly noted in Hachijo Island. In conclusion, global warming in

Okayama might be accelerated more rapidly than that in Tokyo area in recent 50 years.

Keywords: Temper ature, Global Warmin g, Urbanization, Okayama Area

1. Introduction

Global warming has become a serious issue for human

beings. The Fourth report of the Intergovernmental Panel

on Climate Change (IPCC) at 2007 on climate change has

forecast that global warming will have a major impact on

health conditions [1]. Global average temperatures are

projected to increase between 1.8 and 4.0 °C by the end of

21st century [1]. Heat waves such as Shanghai in 1998 and

Paris in 2003 may be representative of the increases in

short-term climate change events [2-5]. It has also reported

that the levels of atmospheric CO2 concentrations are

increasing since the last century [6,7]. In addition, global

warming has accelerated, and changes in temperatures

were remarkably noted since the 1980s, resulting in

increased numbers of heat related disorder in summer

[8,9].

Most cities show a large heat island phenomenon,

registering 5-11˚C warmer than surrounding rural areas

[10]. On local and regional scales, changes in land cover can

sometimes exacerbate the effect of greenhouse-gas-induced

warming, or even exert the largest impact on climatic

conditions.

We have also previously reported that higher

temperatures were closely linked to higher ambulance

transports in Okayama area, Japan [11]. However, accurate

analysis of warming, whether temperature is actually

increasing in Okayama area and what affects this will

have, remain to be investigated.

The aim of this study was to investigate the current

status of global warming in Okayama. In addition, we

compared various parameters of temperatures between

various areas from the viewpoint of the heat island effects.

2. Methods

2.1. Study Area

Okayama area in Okayama Prefecture is on the southern

Changes in Temperatures in Okayama Area Compared with Different Urbanization Areas, Japan163

shore of Honshu Island. The population of 700 000

people is situated on Okayama area. Currently several

public offices of Chugoku district are located in Okayama

area. Although the surrounds of Okayama area had been

used primarily as paddy fields for agriculture, recently

they have undergone rapid changes, developing into

residential and/or commercial areas (Figure 1).

We selected three areas, Tokyo as the city part area,

and Tsuyama or Hachijo Island as the provinces, for the

analysis in comparison with Okayama city, Japan.

Tsuyama area in Okayama prefecture is on the central

of Chugoku area, Japan. The population of 110 000

people is situated on the Tsuyama area. Tsuyama area

had been used primarily as paddy fields for agriculture

compared to Okayama area (Figure 1).

Tokyo area is the largest metropolitan area in Japan

and its population is about 13.0 million. Tokyo central

(8.8 million population, 621 km2) is located in the center

of the metropolitan area, and is mostly urbanized in

Japan (Figure 1).

Hachijo Island (65.52 km2) is located at the south from

Tokyo area (287 km) and the population of 9 000 people

is situated on the Hachijo Island. Island is affected by the

Kuroshio Current (in an oceanic climate zone) (Figure

1).

2.2. Temperatures

Daily, monthly and annual temperatures in Okayama,

Tsuyama, Tokyo area and Hachijo Island in Japan for the

required periods were obtained from Japan Meteorological

Agency (http://www.data.jma.go.jp/obd/stats/etrn/index.

php, accessed 27 Jan, 2010). Mean temperature in Au-

Tsuyama Area

Tokyo Area

Okayama Area Hachijo Island

Figure 1. Four study areas in Japan. (Craft Map: http://

www.craftmap.box-i.net/map.php, accessed 6 Aug, 2010).

gust, mean temperature in a year, mean of the highest

temperatures in August, mean of the highest temperatures

in a year, mean of the lowest temperatures in August and

mean of the lowest temperatures in a year (Okayama area:

1891~2009, Tsuyama area: 1943~2009, Tokyo area:

1876~2009, Hachijo Island: 1907~2009). The number of

days over the level of various temperatures in August

was also used for analysis (1961~2009).

2.3. Statistical Analysis

Pearson’s correlation analysis by using Statistical

Package of SPSS 12.0J for Windows was performed to

examine the significance of the linear relationship among

continuous variables: p < 0.05 was considered to be

statistically significant. In addition, joinpoint regression

program (National Cancer Institute Joinpoint regression

program, version 3.4.3, http://srab.cancer.gov/joinpoint/,

accessed 18 August, 2010) was also used to investigated

the where the different lines of temperatures are

connected together.

3. Results

Simple correlation analysis by Pearson’s correlation

between years and parameters of temperatures in 4 areas is

summarized in Table 1 . All parameters of temperatures in

Okayama area (1891~2009) were significantly correlated

with years. Tokyo area (1876~2009) also showed

significant relationship between various parameters of

temperatures and years (Table 1 ). In Tsuyama area, some

parameters of temperatures i.e. mean temperature in a

year, mean of the highest temperatures in a year and mean

of the lowest temperatures in a year was significantly

correlated with years.

To adjust the observation period, by using data from

1943 to 2009, we also analyzed the relationship between

various parameters of temperatures and years in 4 areas

(Table 2). In Okayama area, all parameters except mean

of the highest temperatures in August, were also

correlated with years. Mean temperature in a year, mean

of the highest temperatures in a year and mean of the

lowest temperatures in a year were significantly correlated

with years in Tsuyama and Tokyo areas. Mean of the

lowest temperatures in August in Tokyo areas was also

correlated with years. However, no parameters were

correlated with years in Hachijo Island.

Correlation coefficients between various parameters of

temperatures and years in Okayama area were the highest

among 4 areas. From single regression line, positive

change in mean temperature for 50 years was corresponded

to 2.05˚C in Okayama area, Japan (Table 2). However,

the change in temperatures was the lowest in Hachijo

Island among 4 areas. In addition, using single regression

line in Tables 1 and 2, positive changes in temperatures

Changes in Temperatures in Okayama Area Compared with Different Urbanization Areas, Japan

164

for 50 years in Table 2 were higher than those in Table 1

in Okayama area. Therefore, positive changes in

temperatures for 50 years were accelerated in Okayama

area. In Tokyo areas, positive changes in mean

temperature in a year and mean of the lowest temperatures

in a year were also accelerated. However, other parameters

in Tokyo areas and Hachijo Island were not accelerated. In

addition, using joinpoint regression program, we analyzed

the point of change in mean temperature in 4 different

areas. The point of change in mean temperatures in

Tokyo was 1921, that in Okayama was 1973 (Figure 2)

and that in Tsuyama was 1984. However, the point of

change in mean temperature in Hachijo Island was not

noted.

Finally, the relationship between the number of days

of over various temperatures which seem to be related to

heat disorder is pointed out and years was also evaluated

(Table 3). The number of days of over 33˚C and 35˚C in

Okayama area was significantly correlated with years.

Especially correlation coefficient between the number of

days of over 35˚C and years in Okayama area was the

highest (r = 0.407, p = 0.0037) (Fi gure 3).

Table 1. Simple correlation analysis between years and paramete r s of temperature in four areas.

r p Single regression line Changes in temperatures (˚C)

for 50 years

Okayama prefecture

Okayama area (f r om 1891 to 2009)

Mean temperature in August 0.416 < 0.0001y = 0.012x + 3.139 0.60

Mean temperature in a year 0.648 < 0.0001y = 0.015x – 14.969 0.75

Mean of the highest temperatures in August 0.328 0.0003 y = 0.012x + 8.965 0.60

Mean of the highest temperatures in a year 0.668 < 0.0001y = 0.012x – 4.023 0.60

Mean of the lowest temperatures in August 0.518 < 0.0001y = 0.015x – 6.511 0.75

Mean of the lowest temperatures in a year 0.580 < 0.0001y = 0.018x – 24.349 0.90

Tsuyama area (from 1943 to 2009)

Mean temperature in August 0.130 0.2939 y = 0.006x + 14.814 0.30

Mean temperature in a year 0.458 < 0.0001y = 0.014x – 13.598 0.70

Mean of the highest temperatures in August 0.043 0.7299 y = 0.003x + 25.890 0.15

Mean of the highest temperatures in a year 0.447 0.0001 y = 0.014x – 8.107 0.70

Mean of the lowest temperatures in August 0.132 0.2866 y = 0.005x + 11.671 0.25

Mean of the lowest temperatures in a year 0.443 0.0002 y = 0.014x – 18.968 0.70

Tokyo prefecture

Tokyo area (from 1876 to 2009)

Mean temperature in August 0.556 < 0.0001y = 0.018x – 8.853 0.90

Mean temperature in a year 0.887 < 0.0001y = 0.025x – 32.904 1.25

Mean of the highest temperatures in August 0.353 < 0.0001y = 0.013x + 0.6077 0.65

Mean of the highest temperatures in a year 0.728 < 0.0001y = 0.015x – 9.010 0.75

Mean of the lowest temperatures in August 0.714 < 0.0001y = 0.025x – 24.606 1.25

Mean of the lowest temperatures in a year 0.917 < 0.0001y = 0.033x – 53.700 1.65

Hachijo island (from 1907 to 2009)

Mean temperature in August 0.285 0.0036 y = 0.006x + 15.136 0.30

Mean temperature in a year 0.350 0.0003 y = 0.005x + 7.624 0.25

Mean of the highest temperature in August 0.249 0.1111 y = 0.007x + 15.819 0.35

Mean of the highest temperature in a year 0.290 0.0029 y = 0.004x + 12.482 0.20

Mean of the lowest temperature in August 0.364 0.0002 y = 0.008x + 8.178 0.40

Mean of the lowest temperature in a year 0.416 < 0.0001y = 0.008x + 0.379 0.40

Changes in Temperatures in Okayama Area Compared with Different Urbanization Areas, Japan165

Table 2. Simple correlation analysis between years and parameters of temperatures in four areas from 1943 to 2009.

r p Single regression line Changes in temperatures (˚C)

for 50 years

Okayama prefecture

Okayama area

Mean temperature in August 0.554 < 0.0001y = 0.031x – 33.852 1.55

Mean temperature in a year 0.833 < 0.0001y = 0.041x – 65.744 2.05

Mean of the highest temperatures in August 0.223 0.0701 y = 0.014x + 4.996 0.70

Mean of the highest temperatures in a year 0.558 < 0.0001y = 0.018x – 14.764 0.90

Mean of the lowest temperatures in August 0.619 < 0.0001y = 0.035x – 45.840 1.75

Mean of the lowest temperatures in a year 0.811 < 0.0001y = 0.053x – 93.859 2.65

Tsuyama area

Mean temperature in August 0.130 0.2939 y = 0.006x + 14.814 0.30

Mean temperature in a year 0.458 < 0.0001y = 0.014x – 13.598 0.70

Mean of the highest temperatures in August 0.043 0.7299 y = 0.003x + 25.890 0.15

Mean of the highest temperatures in a year 0.447 0.0001 y = 0.014x – 8.107 0.70

Mean of the lowest temperatures in August 0.132 0.2866 y = 0.005x + 11.671 0.25

Mean of the lowest temperatures in a year 0.443 0.0002 y = 0.014x – 18.968 0.70

Tokyo prefecture

Tokyo area

Mean temperature in August 0.233 0.0581 y = 0.013x + 0.841 0.65

Mean temperature in a year 0.825 < 0.0001y = 0.035x – 52.678 1.75

Mean of the highest temperatures in August 0.016 0.8956 y = 0.001x + 33.094 –0.05

Mean of the highest temperatures in a year 0.426 0.0003 y = 0.013x – 5.960 0.65

Mean of the lowest temperatures in August 0.396 0.0009 y = 0.022x – 18.966 1.10

Mean of the lowest temperatures in a year 0.889 < 0.0001y = 0.048x – 82.257 2.40

Hachijo island

Mean temperature in August 0.008 0.9505 y = 0.002x + 26.121 0.01

Mean temperature in a year 0.194 0.1152 y = 0.005x + 9.067 0.25

Mean of the highest temperature in August –0.130 0.2938 y = 0.004x + 38.272 –0.20

Mean of the highest temperature in a year 0.073 0.5565 y = 0.002x + 17.722 0.10

Mean of the lowest temperature in August 0.113 0.3625 y = 0.004x + 17.188 0.20

Mean of the lowest temperature in a year 0.153 0.2175 y = 0.004x + 7.593 0.20

Figure 2. Change point of annual mean temperatures in Okayama, Japan (1891~2009).

Changes in Temperatures in Okayama Area Compared with Different Urbanization Areas, Japan

166

Table 3. Simple correlation analysis between years and number of days over various temperatures in August from 1961 to

2009.

Okayama area Tsuyama area Tokyo area Hachijo island

r p r p r p r p

Number of days over

30˚C 0.071 0.6301 0.053 0.7169 0.016 0.9113 0.118 0.4213

Number of days over

31˚C 0.073 0.6184 0.004 0.9799 0.074 0.6127 0.107 0.4628

Number of days over

32˚C 0.173 0.2346 0.086 0.5552 0.023 0.8731 0.085 0.5637

Number of days over

33˚C 0.343 0.0159 0.069 0.6384 0.077 0.5968 0.058 0.6905

Number of days over

34˚C 0.266 0.0643 0.101 0.4917 0.130 0.3748

Number of days over

35˚C 0.407 0.0037 0.000 0.9978 0.125 0.3929

4. Discussion

We firstly investigated the changes in parameters of

temperatures among 4 different urbanization areas such

as Okayama, Tsuyama, Tokyo areas and Hachijo Island,

Japan. Parameters of temperatures were gradually

increased with years in Okayama area, especially in

recent years. In addition, the change point of 1973 in

mean temperature may be reflected that heat island effect

in Okayama area was remarkably accelerated.

According to the research of Osaka in Japan, the mean

warming rate in Osaka surface air temperature is about

2.0˚C over the period from 1883 to 2006, at least half of

which can be attributed to the urban heat island effects [12].

However, this surface air temperature warming was not as

strong as the ground warming recorded in the subsurface

temperature profiles. Therefore, the anthropo- genic

thermal impacts on the subsurface can be more persistent

and profound than the impacts on the atmosphere.

Figure 3. Simple correlation analysis between the number

of days over 35˚C and years in Okayama area, Japan

(1961~2009).

In some previous reports, the relation between high

temperatures and heat stroke in Japan [16-18]. Nakai et

al. investigated heat-related deaths in Japan from 1968

through 1994 and heat-related deaths were most prone to

occur on days with a peak daily temperature above 38˚C

[16]. In addition, they reported that incidence of heat-

related deaths showed and exponential dependence on

the number of hot days [16]. Piver et al. reported that

heat stroke was associated with prolonged exposures to

higher air temperatures that usually occur in the summer

months of July and August in 1980-1995 in Tokyo.

Residents in Tokyo were also often exposed simultaneously

to high concentrations of air pollutants [17]. Qui et al.

reported that an unusual hot spell in 1999 was followed

by a high mortality rate in Hokkaido, Japan [18]. We

have also previously showed that higher temperatures

were closely linked to ambulance transports in Okayama

area, Japan [11].

Taniguchi et al. reported that subsurface environmental

indicators were evaluated from three points of view i.e.

human activities, climate change, and character of

urbanization and social policies. Heat island effect due to

urbanization creates subsurface thermal contamination in

many cities [13]. Average subsurface temperature profiles

in four Asian cities (Tokyo, Osaka, Seoul and Bangkok)

were compared and analyzed to evaluate the effects of

surface warming [14]. The magnitude of surface warming

is evaluated to be the largest in Tokyo (2.8 ˚C), followed by

Seoul, Osaka and Bangkok. And this observation showed

mean depth of deviation from the regional geothermal

gradient in each urban area may be a useful indicator of the

history of urbanization. The combination of the heat island

effect due to urbanization and global warming on

subsurface temperatures also relates to global ground water

quality issues. This relationship holds because increased

subsurface temper- atures alter the ground water system

chemically and microbiologically [15].

In this study, we compared points of change in mean

temperature among 4 areas, and we found that point of

Changes in Temperatures in Okayama Area Compared with Different Urbanization Areas, Japan167

change in mean temperature in Tokyo was 1921, that in

Okayama was 1973 and that in Tsuyama was in 1984.

Therefore, it seems reasonable to suggest that simply

dealing with heat island effect in Okayama area i.e.

innovation of the thermal energy metabolism in cities

and individual coping with high temperatures is urgently

required in Okayama as well as Tokyo area, Japan. In

addition, the point of change in mean temperature may

be good parameter of urbanization in Japan.

Potential limitation still remains in this study. The

changes in parameters of temperatures, which were noted

in 4 areas, may not apply for all areas in Japan. Therefore,

we could not accurately evaluate the changes in

temperatures in Japan. Further studies are required to prove

the changes in temperatures and heat island effect in Japan.

In conclusion, the mean temperature in Okayama area

is rising intentionally higher than that in Tokyo area,

especially in recent years. The number of days of over

33˚C and 35˚C in only Okayama area was significantly

correlated with years.

5. Acknowledgements

We gratefully thank to Mrs. Michiyo Mitani for

assistance of data preparation.

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