179

Present Situation of Outdoor Wind Environmental Issues in Japan
Ryuichiro YOSHIE* and Masaaki OHBATokyo Polytechnic University
1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan*e-mail: yoshie@arch.t-kougei.ac.jp

Abstract
This article introduces the current status of outdoor environmental issues in Japan. The outdoor
environment is greatly affected by various wind conditions, commonly classified as strong winds and weakwinds. Strong winds around high-rise buildings have been a social issue for over 30 years in Japan. Windtunnel experiments have been conducted to assess the environmental impact of strong winds at the pedestrian level and are regarded as the most reliable prediction method. In recent years, the application ofcomputational fluid dynamics (CFD) to this problem has been rapidly gaining popularity and acceptance. To
ensure the reliability of CFD simulations, “AIJ guidelines for practical applications of CFD to pedestrianwind environments around buildings” was published in 2007.
On the other hand, weak wind conditions can also cause problems. Air pollution and the heat island
phenomenon intensify when winds are weak. Owing to the restrictions on the emission of harmful substances from both facilities and automobiles, Japan’s outdoor air quality has been gradually improving. The
annual averages of NO2, SO2, CO, and SPM concentrations have remained steady or gradually declined inrecent years, but the compliance rates with the Environmental Quality Standards have been extremely low
for photochemical oxidants. Heat island phenomenon currently occurs in most cities in Japan due toanthropogenic heating, poor urban ventilation and oversized artificial ground coverage areas. Several
countermeasures have been taken by governmental authorities. Recent researches on urban heat islands inJapan are reviewed in the latter part of this article.
Key words: air pollution, CFD, heat island phenomenon, pedestrian wind environment,
wind tunnel experiment

1. Introduction
Winds have a great influence on the outdoor environment in urban areas. Problems they cause roughly beclassified into strong wind and weak wind issues. The
first half of this article addresses strong-wind issues, i.e.,strong winds around high-rise buildings. This article
introduces the current situation of the pedestrian windenvironment around high-rise buildings, environmental
impact assessment methods using wind tunnel experiments and computational fluid dynamics (CFD), and thecriteria for assessment in Japan. Next, the paper considers the outdoor air pollution problem and the heat island
phenomenon, both of which are more serious in
weak-wind regions in urban street canyons. The importance of air ventilation in urban areas is now broadly
recognized as a countermeasure to the urban heat island
phenomenon and air pollution problem, so it is becoming extremely important to ensure adequate air ventilation in urban spaces. Nowadays, researchers in the fieldof environmental wind engineering are paying more
attention to these weak-wind-related issues as opposed
Global Environmental Research
13/2009: 179-188
printed in Japanto strong-wind issues. The middle part of this paper
describes environmental quality standards and laws foroutdoor air pollutants and the present situation of outdoor air pollution in Japan, based on the Environmental
White Paper (Ministry of the Environment, Governmentof Japan (2009)). Lastly, the paper reviews several countermeasures taken by the government authorities andrecent studies on urban heat islands in Japan.

2. Pedestrian Wind Environment Around
High-rise Buildings
2.1 Present situation of the pedestrian windenvironment
Strong winds around high-rise buildings have been asocial issue for more than three decades in Japan. Conflicts between construction companies and residents are
not unusual, and occasionally develop into lawsuits.
Although the assessment of the pedestrian wind environment is not regulated by Japanese law, some local
governments require developers to make preliminary
investigations, estimates and assessments regarding the©2009 AIRIES180

R. YOSHIE and M. OHBA

environmental impact of their development projects. For
example in Tokyo, developers who plan to build ahigh-rise building over 100 m in height with a total floorarea of over 100,000m2 must carry out procedures according to the “Environmental Impact Assessment Ordinance of the Tokyo Metropolitan Government.” Windtunnel experiments or CFD simulations are typicallycarried out for this kind of environmental impact assessment.
2.2 Assessment of the pedestrian wind environment
by wind tunnel experiment
In the wind tunnel experiments for this type ofassessment, multi-channel thermistor anemometers arewidely used in Japan to measure wind speed. Since theanemometers are relatively strong and hard to break,they can be installed from under the turntable, as shownin Fig. 1. Once the anemometers are set at the measuring
points, wind speeds of many points can be measured at
the same time. Therefore, it does not take too much time
to measure the wind speeds of many wind directions andof several experimental cases. However, the frequency
response of the anemometers is low (lower than 1Hz).
The gust wind speeds cannot be measured with this typeof anemometer. This is one of the problems in estimating the occurrence frequency of maximum gust speeds
as will be described later.
2.3 Assessment of the pedestrian wind environment
by CFD simulations
The application of CFD to the prediction of windenvironments has been rapidly increasing. Despite its
widespread use, the accuracy of prediction and manyfactors that affect the simulation results are still not thoroughly understood. In order to clarify the ambiguities
and make practical guidelines for CFD prediction of thewind environment, a working group was organized by
the Architectural Institute of Japan (AIJ) in 1997. This
group consists of researchers from several universities
and private companies. The working group has con-ducted various comparative studies as follows.
・ Flow field around a high-rise building without
neighboring buildings, as shown in Fig. 2
・ Flow field around a high-rise building within amodel city block, as shown in Fig. 3
・ Flow field behind a tree canopy, as shown in Fig. 4.
・ Flow field around high-rise buildings in actual urban
areas, as shown in Fig. 5.
The results of CFD were compared with those ofwind tunnel experiments and field measurements, andmany factors such as computational domain, grid,boundary conditions, numerical schemes for advection
terms, and turbulence models were examined to clarify
their influence on the simulation results (Yoshie et al.,2007).
Based on these investigations, “AIJ guidelines forpractical applications of CFD to pedestrian windenvironments around buildings (2007)” was publishedin 2007 (Fig.6). An English version was also publishedin 2008 (Tominaga et al., 2008).

b

wind
Wind

4b

H=2b
4b

b
b

(a) 2:1:1 square prism(b) 4:4:1 square prism

Fig. 2 Flow field around a single high-rise building.

Fig. 3 Flow field around a high-rise building within a modelcity block.

Fig. 1 Multi-channel thermister anemometers installed inbuilding models.

Fig. 4 Flow field behind tree canopy.

Present Situation of Outdoor Wind Environmental Issues in Japan(a) Niigata city

181(b) Shinjuku

Fig. 5 Flow field around high-rise buildings in actual urban areas.
Table 1 Criteria for assessment of pedestrian wind environment
based on occurrence frequency of daily maximum gustspeed.

Table 2 Criteria for assessment of pedestrian wind environments based on cumulative frequency of mean windvelocity.

Fig. 6 AIJ guidebook for numerical simulation of thewind environment in urban areas.

2.4 Criteria for assessment of wind environment atpedestrian level
The occurrence frequencies of wind speeds at thepedestrian level can be calculated using statistical winddata from a nearby meteorological observatory and theresults of wind tunnel experiments or CFD simulation.
One of the most widely used methods for assessing thewind environment is based on the occurrence frequencyof the daily maximum gust speed proposed by
Murakami et al. (1983) as shown in Table 1. The otherassessment method based on the cumulative frequencyof mean wind speeds (averaged over 10-minute periods)
proposed by the Wind Engineering Institute (1989) asshown in Table 2 is also widely used in Japan.
Murakami et al. (1983) conducted long-term observations of wind speed and wind-induced problems incooperation with many inhabitants in downtown Tokyo.

The criteria were determined considering the relationships between the daily maximum gust speeds andimpressions of the wind environment or wind-induced
problems.
As mentioned above, because multi-channel thermistor anemometers with poor frequency response are usedin the wind tunnel experiments, gust wind speeds cannot
be obtained from the experiments. Furthermore, most of
the CFD simulations for the assessments are based on
Reynolds averaged turbulence models, so the obtained
results are mean wind velocities and not gust wind182

R. YOSHIE and M. OHBA

velocities. Therefore, when using Murakami’s criteria,
the gust factor (the ratio of peak gust wind velocity tomean wind velocity) has to be assumed. However theoccurrence frequency of the daily maximum gust speed
strongly depends on the assumed gust factor. Nishimura& Takamori (2002), and Hongo & Nakayama (2003)
have proposed gust factor estimation methods, but wehave not reached a general consensus about the determination of the gust factor yet.

3. Outdoor Air Pollution
3.1 Environmental quality standard and laws foroutdoor air pollutants
Table 3 indicates Environmental Quality Standards(EQS) for SO2, CO, SPM, NO2, and Ox specified in the“Basic Environmental Law.” Other than these substances, EQS for benzene, trichloroethylene, tetrachloroethylene, dichloromethane, and dioxins are also
specified in the “Basic Environmental Law” The EQS
are policy objectives which are desirable for the protection of human health and conservation of the living
environment. The “Air Pollution Control Law” restricts
the emission of soot and smoke, volatile organic compounds, and particulates from factories and facilities.
The Law also specifies maximum permissible limits on
the amount of exhaust gases from motor vehicles. In
areas where factories are concentrated and it is considered difficult to maintain EQS, the total load control isenforced for factory units according to the total amountreduction program prepared by the governor of eachprefecture.

3.2 Present situation of outdoor air pollution
Owing to the restrictions of the “Air Pollution Control Law” on emission of harmful substances for bothfacilities and automobiles, the outdoor air quality has
been gradually improving in Japan.
According to the Environmental White Paper (Ministry of the Environment, Government of Japan, 2009),
the annual average nitrogen dioxide (NO2) concentration
at 1,379 Ambient Air Pollution Monitoring Stations(AAPMSs) was 0.013ppm and that at 431 Roadside Air
Pollution Monitoring Stations (RAPMs) was 0.025ppm
in FY 2007. The environmental quality standards (EQS)
for nitrogen dioxides specify that the daily average ofhourly values shall be within the range of 0.04 - 0.06
ppm or below this zone (Table 3). NO2 concentrations
have achieved a 100% compliance rate with the EQS at
the AAPMSs and 94.4% at the RAPMs. Compliancewith the EQS in areas designated for measures under the“Law concerning Special Measures for Total Emission
Reduction of Nitrogen Oxides and Particulate Matterfrom Automobiles in Specified Areas” (Automobile
NOx/PM Law) was 90.6% in FY2007, a marked
improvement from 43.1% in FY1998.
The annual average sulfur dioxide (SO2) levels in FY
2007 were 0.003 ppm at ambient stations (AAPMSs)
and roadside stations (RAPMSs), both remaining continuously at almost the same levels over the past several
years. The environmental quality standards for SO2
indicate that the daily average for hourly values shallnot exceed 0.04 ppm, and the hourly values shall not
exceed 0.1 ppm (Table 3). The compliance rates with the
EQS for SO2 were 99.8% at AAPMSs and 100.0% at

Table 3 Environmental Quality Standards in Japan.

Substance
Sulfur dioxide(SO2 )

Carbon monoxide(CO)Suspendedparticulate matter(SPM)

Environmental conditions

Measuring method

The daily average for hourly values shall not
exceed 0.04 ppm, and hourly values shall
Conductometric method or ultraviolet
not exceed 0.1 ppm
fluorescence method(Notification on May 16, 1973)
The daily average for hourly values shall not
exceed 10 ppm, and average of hourly
Nondispersive infrared analyzer method
values for any consecutive eight hour
period shall not exceed 20ppm(Notification on May 8, 1973)
Weight concentration measuring methods based
The daily average for hourly values shall not on filtration collection, or light scattering method;
exceed 0.10 mg/m³, and hourly values shall or piezoelectric microbalance method; or β-ray
attenuation method that yields values having a
not exceed 0.20 mg/m³
linear relation with the values of the above(Notification on May 8, 1973)
methods.

Nitrogen dioxide(NO2)

The daily average for hourly values shall be Colorimetry employing Saltzman reagent (withwithin the 0.04-0.06 ppm zone or below that Saltzman's coefficient being 0.84) or
chemiluminescent method using ozone.
zone (Notification on July 11, 1978)

Photochemical
oxidants(Ox)

Hourly values shall not exceed 0.06 ppm(Notification on May 8, 1973)

Absorption spectrophotometry using a neutral
potassium iodide solution; coulometry; ultraviolet
absorption spectrometry; or chemiluminescentmethod using ethylene.

1. Suspended particulate matter is defined as airborne particles with a diameter smaller than or equal to 10 µm.
2. Photochemical oxidants are oxidizing substances such as ozone and peroxiacetyl nitrate produced by photochemical
reactions (only those capable of isolating iodine from neutral potassium iodide , excluding nitrogen dioxide.)Present Situation of Outdoor Wind Environmental Issues in Japan

RAPMSs in FY2007, showing satisfactory conditions inrecent years.
The environmental quality standards for carbon
monoxide (CO) indicate that the daily average of hourly
values shall not exceed 10 ppm, and average of hourly
values for any consecutive eight hour period shall not
exceed 20 ppm (Table 3). The annual average values in
FY 2007 were 0.4 ppm at AAPMSs and 0.5 ppm at
RAPMSs, showing a gradual decrease in recent years.
The compliance rates with the EQS for CO have been
100.0% for both AAPMSs and RAPMs.
The environmental quality standards for Suspended
Particulate Matter (SPM) indicate that the daily averagefor hourly values shall not exceed 0.10 mg/m3, andhourly values shall not exceed 0.20 mg/m3 (Table 3).
The annual averages of SPM concentrations were0.024mg/m3 at AAPMSs and 0.027mg/m3 at RAPMSs
in FY2007. The compliance rates with the EQS were
52.5% at AAPMSs and 34.3% at RAPMSs in FY 2002.
In FY 2001, under the Automobile NOx/PM Law,particulate matter was added to the list of substances tobe regulated. Owing to the law, compliance rates have
improved to 89.5% at AAPMSs and 88.6% at RAPMSs
as of FY 2007.
Photochemical oxidants are the cause of photochemical smog. In almost all regions throughout Japan,
photochemical oxidants still exceed the environmental
quality standards (EQS) (an hourly value of 0.06 ppm or
less: see Table 3). The compliance rate with the EQS in
FY 2007 was as extremely low as 0.2% at AAPMSs and
RAPMs. The number of days with warnings issued on
photochemical oxidants has risen to 144 (in 25 prefectures). There were 400 persons who reportedly suffereddiscomfort caused by photochemical air pollution. Air
pollution due to photochemical oxidants is expected to
improve through restricting the emission of nitrogenoxides and volatile organic compounds. To reducehydrocarbons discharged from automobiles, restrictionof exhaust gas has been enforced since 1973 in accordance with “the Air Pollution Control Law” issued in1968. Subsequently, these restrictions have been successively renewed.

4. Heat Island Phenomenon
The heat island phenomenon, in which the airtemperature in urban areas is higher than in suburban
areas, is now found in most large cities. According to
the Third Assessment Report of the Intergovernmental
Panel on Climate Change (IPCC) in 2001, it is estimatedthat the average global surface temperature increased by
0.6°C ± 0.2°C during the 20th century. However, inmajor cities such as Tokyo and Nagoya, the averagetemperature increased by 2°C - 3°C during the same
period. Thus, compared with the mean change in the
global climate, the increasing trend of heat islands inurban areas is remarkable. With these increases in air
temperature, the numbers of “tropical nights” in which
the temperature exceeds 25°C at night have been

183

increasing in many cities. The annual number of thetropical nights in Tokyo was on the order of several daysin the early 20th century, while it has reached a level of
30 to 50 days in recent years. Furthermore, the area overwhich this phenomenon extends is increasing. This has
detracted from the city's pleasant environment and has
also created thermal pollution problems.
At present, a lot of administrative countermeasures
are being taken against the heat island effect and studies
have been performed to find ways to cope with the heatisland problem. Among these countermeasures, recent
attention has focused on the creation of ventilation paths
in urban areas at the urban planning stage. In September
2006, a symposium entitled “Air Change and Ventilation
Paths in Urban Areas” was held by the Architectural
Institute of Japan. In this chapter, we review several
countermeasures taken by administrative authorities andrecent researches on the heat island phenomenon in
Japan.
4.1 Administrative countermeasures against theheat island effect4.1.1 Recent actions taken by administrative
authorities
The Japanese government and local public organizations have taken various countermeasures and actions to
mitigate the problem of the heat island effect. For thesecountermeasures to be effective, it is necessary to promote mutual cooperation among the relevant organizations and to take systematic action. An Inter-Ministry
Coordination Committee was formed to mitigate urban
heat island effects, and a basic policy has been determined in March 2004. As a result, the “General Principle of the Countermeasures to cope with the Heat Island
Problem” was publicized. This systematically summarized actual measures to be taken (Governmental
Liaison Council on Countermeasures Against the Heat
Island Effect, 2004). In July 2004, the Ministry of Land,
Infrastructure and Transport presented “Guidelines on
Building Design for the Alleviation of Heat Island
Phenomena” to local administrative authorities. In July
2005, CASBEE-HI (Comprehensive Assessment System
for Building Environment Efficiency on Heat Island
Relaxation) was publicly announced. In August 2006,
the “International Workshop on Countermeasures toUrban Heat Islands” was held in Tokyo under the joint
sponsorship of the Ministry of Land, Infrastructure andTransport and the International Energy Agency.
4.1.2 General principle of the countermeasures tocope with the heat island effect
The Governmental Liaison Council on Countermeasures Against the Heat Island Effect promulgatedgeneral guidelines in March 2004 as mentioned above.
These guidelines focused on four major policies:①reduction of anthropogenic heat, ②improvement ofground cover, ③improvement of urban forms, and④modification of lifestyles. It also recommended re-

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R. YOSHIE and M. OHBA

inforcing the atmospheric monitoring network andpromoting research on the effects of these countermeasures.
(1) Reduction of anthropogenic heat
Anthropogenic heat is exhausted from air-conditioning units, electric devices, combustion facilities, motor
vehicles, etc. Various measures have been taken to
reduce anthropogenic heat. Some specific ones include:
production of high-efficiency energy-consuming equipment, construction of houses and buildings with highenergy-saving effects, development of low-emission
vehicles, and taking measures to improve traffic
distribution and encourage the use of public transportation. Table 4 indicates the targets for energy-saving performance in houses and buildings.
(2) Improvement of ground surface cover
Improving ground surface conditions may effectively
retain water and prevent high temperatures on the
ground surface. The target was to achieve open public
spaces in urban areas with water and green areas from
12 m2 per person in 2002 to 13 m2/person in 2007, i.e.,
an increase of about 10%.
(3) Improvement of urban forms
Ventilation paths from green belts and water surfaces
are thought to improve the thermal environment inurban areas very effectively. While conserving green
spaces in urban areas, it is necessary to establish a firm
network of water and green areas, so as to encourage thedevelopment of cities with lower environmental load.
For long-term planning, the target is to establish moderate-sized urban areas with low environmental loads.
(4) Improvement of life styled
To alleviate the heat island effect closely associatedwith social and economic activities in urban areas,
actions are now being taken with the aims of improving
the life style of the inhabitants. Specifically, it is aimed
to reduce carbon dioxide emission by 440,000 tons –850,000 tons by setting the air-conditioning temperature
to 28°C in summer and the heating temperature to lessthan 20°C in winter.
4.2 Recent researches on countermeasures against
the heat island effect4.2.1 Numerical simulations
To evaluate the heat island effect, it is important tounderstand correctly the heat flux within an urban area
Table 4 Energy-saving efficiency of houses and buildings.
Newly built houses
Newly built buildings

1999
5%
34%

2005
23%
70%

2008
50%
80%

Note 1:The energy-saving efficiency of houses is the ratio of houses
complying with energy-saving standards of the Energy-Saving
Act to houses newly built that year.

Note 2:The energy-saving ratio of buildings is the ratio of floor areas ofbuildings complying with “Judgment Standards” of the EnergySaving Act to those of the buildings (with an area of 2,000 m2 ormore) confirmed during the year.

and to elucidate the structure of the heat island. Satoet al. (2008a) established a method of evaluating theheat balance over an entire urban area from the resultsof numerical analyses based on a meteorological mesoscale model and they used it to analyze the heat islandeffect in the urban area of Tokyo. Most cities in Japanare located along the sea coast, and sea breezes exert a
considerable influence on the regional climatic characteristics as a cooling source. Ooka et al. (2008) proposed a mean kinetic energy balance model based on themeso-scale climate analysis to estimate the structure of
the sea breeze. The balances of four areas in the Tokyo
metropolitan were analyzed by using this method. It wasclarified that the sea breeze was interrupted by the resistance and turbulence caused by buildings at the inter city.
Furthermore, they (Sato et al. 2008b) proposed a newconcept “moving Control Volume” along the sea breeze
in order to clarify the interaction between sea breeze andurban climate. By using this model, they investigated
the sensible heat, latent heat and mean kinetic energybalances of the moving Control Volume. Sasaki et al.
(2008) proposed a “heat balance map” for Sendai City
based on a meso-scale numerical climate analysis. This
“heat balance map” illustrated the areas where theinfluence of sea breezes was significant in contrast withheat generated from ground surfaces and anthropogenic
heat release, and it could be used as the basis of a newcity planning and urban canopy project. In order toaccounts for drag force by buildings and heat transfer
inside the urban canopy, Ashie & Vu (2004), Harayama
et al. (2005) and Kawamoto & Ooka (2009) incorporated the urban canopy model with the metrologicalmeso-scale model.
However, the analysis based on the metrologicalmeso-scale model described above cannot evaluate
winds in detail that flow between buildings or along
streets and rivers. To analyze wind flows that are
tiny-scale compared to meso-scale flows, it is necessary
to perform a micro-scale CFD analysis with buildings
and trees adequately reproduced. Ashie et al. (2007)
applied a large-sized parallel computer called an “Earthsimulator” to the study of urban environmental problems. Specifically, large-scale numerical calculations
were performed for 10 square kilometers in the Tokyo
Bay area with 5 m × 5 m horizontal grids. By accuratelyreflecting the arrangement of buildings, topography andland utilization, the wind flows through spaces between
rivers, canals and buildings were reproduced, and air
ventilation performance in the area was clearly evaluated from the viewpoint of alleviation of the heat islandeffect. Furthermore, Kataoka et al. (2006) has applied
Large Eddy Simulation to a study on the climate in the
Shinjuku area of central Tokyo and evaluated theblockage effect of high-rise tower buildings on sea
breezes. In order to quantitatively clarify the effect ofvarious relaxation measures to the heat island phenomenon, Tsuchiya et al. (2008) conducted coupled numerical simulations of convection, radiation and conduction
in Otemachi area, as a high-rise office block, and inPresent Situation of Outdoor Wind Environmental Issues in Japan

Kyobashi area, as a middle-rise office block in Tokyo.
The result showed that the measures of high albedo
material and greening on ground and road were effective
in Otemachi, and heat release point and way of airconditioning affect very much in Kyobashi.
4.2.2 Field measurements
Recently in Tokyo, high-rise tower buildings havebeen constructed along the bay. They are said to have
prevented the penetration of sea breezes into the downtown area. Mikami et al. (2006) performed fieldmeasurements in downtown Tokyo. From airflow
characteristics and air temperature distributions, he indicated that the temperature in the wake region ofhigh-rise tower buildings was 2°C - 3°C higher than thatnear an upwind large green space. Taniguchi et al. (2008,2009) carried out the field measurement in the urban
district in Hiroshima City. They measured wind velocity
and temperature in the sea breeze in summer. They
showed mitigation effect of the sea breeze and river
breeze for heat island phenomenon in Hiroshima.
Hashimoto & Horikoshi (2008) clarified the effect of thesea breeze blowing over the Horikawa Canal on theurban climate in Nagoya by field measurements at
10 fixed points along the canal. They observed that thesea breeze proceeded along the Horikawa Canal up to
9 km from the sea.
4.2.3 Reflective painting and greening on buildings
and ground surfaces
Studies have been performed on light-colored surfaces intended to reduce solar absorption on roofs andwalls of buildings and on the ground to determine theireffectiveness in mitigating the heat island effect. It was
found that they suppress increases in ambient temperature and heat storage in ground coverage and building
frames. Roof coatings with highly reflective materials
are called “Cool roofs.” A Cool Roof Committee wasalso established in the Architectural Institute of Japan,
and studies have been carried out to determine theperformance of cool roofs and walls in alleviating theheat island effect. The Tokyo Metropolitan Governmentis actively promoting the adoption of roof greening androof coatings with highly reflective materials. Kondo
et al. (2008) conducted field measurements on pavement
where two areas of surface were coated with high reflective paint and ordinary material. The heat flux on theurban surface was calculated on the basis of heat budget
equation with the measured data, and the result wascompared with the artificial heat release from buildings
etc. in 23 wards of Tokyo. They showed that the highreflective pavement (cool pavement) could reduce sensible heat flux from pavement to urban air and it was very
effective to relax the heat island problem. But they
pointed out the possibility that the surface temperatureof human body and SET* became higher on the coolpavement than those on ordinary pavement according to
the amount of reflective heat (Kondo et al. 2009). Satoet al. (2004) analyzed the environmental influence by

185

greening and high albedo surface. In summer season,
they have great effect on urban thermal environment. On
the other hand, they had less impact in the winter season.
Hirano (2005) quantified the mitigation effect of urban
greening on urban heat island and its effects on energy
consumption for air-conditioning and water heating. A
scenario of urban greening was that the vegetation
coverage in Tokyo metropolitan increased by 11.8%.
Urban climate simulations were conducted using a
meso-scale meteorological model and the energy consumption of air-conditioning and water heating wasestimated based on the simulated air temperatures. Theenergy consumption decreased by 13.8TJ/day on a typical summer day, and increased by 6.7TJ/day on a typicalwinter day. Ichinose et al. (2006) investigated heat andwater budget characteristics of rooftop greening basedon long term actual measurement, and estimated mitigation effect of heat island phenomenon.
4.2.4 Wind tunnel experiments on urban ventilation
Urban ventilation is one of the effective countermeasures for the heat island phenomenon. The urban ventilation is greatly dependent on urban forms. There aresome recent researches on this issue based on wind tunnel experiments. Kubota et al. (2007) investigated therelationship between the building density and the average wind velocity at pedestrian level in residential
neighborhoods. They conducted wind tunnel tests on 22
residential neighborhoods selected from actual Japanesecities. The results show that there is a strong relationshipbetween the gross building coverage ratio and the mean
wind velocity ratio. They proposed guidelines for realizing acceptable wind environment in residential
neighborhoods using the gross building coverage ratio.
Yoshie et al (2008) investigated characteristics of air
ventilation and thermal environment in a built-up areawith closely-packed high-rise buildings by wind tunnel
experiments. As the experimental results, spatial averageof wind velocity ratios at pedestrian level could be expressed by “vertical average of gross building coverage
ratio”, and the height variation of buildings was very
effective for improving the air ventilation and the thermal environment in this dense area. The height variationbuildings increased the vertical transport of air and heat
both by advection and turbulent diffusion. They called
this effect “vertical ventilation path”. On the other hand,
Hagishima et al. (2007) investigated a bulk drag coefficient of rectangular blocks in a wind tunnel, and theyfound out the height variation of blocks makes the bulk
drag coefficient large.
4.2.5 Comprehensive assessment system ofbuilding environmental efficiency
CASBEE is a method of evaluating and rating buildings for their environmental efficiency (Murakami et al.
2006-1, 2006-2, 2007). It is a comprehensive system forassessing building environmental efficiency, including
not only the reduction of environmental load such asenergy-saving, resource-saving and recycling efficiency,

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R. YOSHIE and M. OHBA

but also environmental quality and improvement of efficiency by taking indoor comfort and various scenarios
into account. The CASBEE assessment has been developed in accordance to the following three concepts:• Assessment can be made throughout the life cycle
stages of the buildings.
• Assessment can be made from two viewpoints: the“environmental quality and building efficiency (Q)”and “environmental load of the buildings (L).”• Assessment is made using the newly developed
assessment index BEE (building environmental efficiency) based on the concept of “environmental efficiency”.
Under BEE, buildings are given 5-step ratings.
CASBEE utilizes four basic tools depending on thelife-cycle stage of the buildings and additional extended
tools to suit individual purposes. These are collectively
called the “CASBEE Family.” Of these, CASBEE-HI
has been developed as a tool for assessing the alleviation of the heat island effect in buildings (Murakami
et al., 2006a, 2006b, 2007). This plays a role in detailed
and quantitative evaluation of items to be assessedwhich relate to the heat island effect. It performs detailed assessment of the outdoor thermal environment
and the heat island load. In CASBEE-HI, the environmental efficiency (BEEHI) of the alleviation of the heatisland effect is evaluated by the following equation:
BEE Hi =

QHI
=
LHI

improvement of thermal environment inside the virtual boundary
Heat island load outside the virtual boundary

CASBEE-HI is now widely used for evaluating and rating newly planned buildings and existing buildings.
4.3 Future works and prospects
The present researches on countermeasures for heatisland phenomenon might not have reached the sufficient level to correctly evaluate their effects. There arestill many uncertainties in meso-scale numerical climate
analysis. Most of the researches using CFD simulation
are based on RANS models which cannot precisely predict the flow and temperature field in weak wind region
in the street canyon. We have to continuously makeefforts to improve and assure the quality of these models
that are applied for predicting flow and heat transport
processes in urban environments. We also don’t haveenough evidence for urban form planning which relax
the urban heat island. For example, height variation ofbuildings improve urban ventilation of that area, but
momentum and cool heat of the wind is consumed atthat area, and then the wind velocity might decrease andair temperature might increase in the leeward areas.
Which is fair and reasonable we consume cool energy ofsee breeze in coastal areas or inland areas? The promising method to answer this question is meso-scale
numerical climate analysis incorporated with urban canopy model. However parameters in the canopy modelsuch as drag force coefficients and heat transfer coeffi-

cients etc. on different urban forms are not clarified yet.
We have to build universal models to evaluate theseparameters based on the wind tunnel experiments andlarge eddy simulations.

5. Conclusions
The paper has demonstrated the present status of outdoor wind environmental issues and studies in Japan
based on recent researches and reports, and one cansummarize the results as follows:
1) For the environmental impact assessment ofstrong winds around high-rise buildings, researchers
often carry out wind tunnel experiments or CFD simulations. In particular, use of the CFD method has been
rapidly increasing. To ensure the reliability of CFD
simulations, “AIJ guidelines for practical applications of
CFD to the pedestrian wind environment around buildings” was published in 2007.
2) The criteria for assessing the wind environment
based on the occurrence frequency of daily maximum
gust speed proposed by Murakami et al. and the criteria
based on the cumulative frequency of mean wind velocities (averaged over 10-minute periods) proposed by theWind Engineering Institute are widely used in Japan.
3) The “Basic Environmental Law” specifies environmental quality standards (EQS) for SO2, CO, SPM,
NO2, Ox, benzene, trichloroethylene, tetrachloroethylene, dichloromethane and dioxins
4) The “Air Pollution Control Law” restricts theemission of soot and smoke, volatile organic compounds
and particulates from factories and facilities. The Law
also specifies maximum permissible limits on theamount of exhaust gases from motor vehicles.
5) Owing to the restrictions on emission of harmful
substances from both facilities and automobiles, the outdoor air quality has been gradually improving in Japan.
The annual averages of NO2, SO2, CO, and SPM
concentrations have remained steady or gradually
declined in recent years, but the compliance rates with
the Environmental Quality Standards were extremely
low for photochemical oxidants.
6) The compliance rates with the EQS in FY 2007
were as follows.
･NO2： 100% at Ambient Air Pollution Monitoring
Stations (AAPMSs), 94.4% at Roadside Air
Pollution Monitoring Stations (RAPMs) and
90.6% at areas designated by the Automobile
Mox/PM Law･SO2： 99.8% at AAPMSs and 100% at RAPMs･CO： 100% at AAPMSs and 100% at RAPMs･SPM：89.5% at AAPMSs and 88.6% at RAPMs･Ox： 0.2% at (AAPMSs) and at (RAPMs)
7) The governmental liaison council on countermeasures against the heat island effect has publicly announced the “General Principle of the Countermeasures
to Cope with the Heat Island Problem” in 2004. This has
systematically summarized actual measures to be taken.

Present Situation of Outdoor Wind Environmental Issues in Japan

8) Resent researches in Japan on countermeasuresagainst the heat island effect (numerical simulation,
field measurement, wind tunnel experiment, reflective
painting and greening) were reviewed.
9) Murakami et al. has proposed CASBEE-HI(Comprehensive Assessment System of Building Environmental Efficiency for Heat Island Relaxation) in
2006, and it is now widely used for evaluating and rating buildings for their environmental efficiency.
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Ryuichiro YOSHIE
Ryuichiro YOSHIE is a professor at the
Department of Architecture, Faculty ofEngineering, Tokyo Polytechnic University
since 2004. He graduated with a BA from
Kyoto University in 1984. Before joining
Tokyo Polytechnic University, he worked in
Maeda Corporation (construction company,“Maeda Kensetsu Kogyo” in Japanese) from1984 to 2003. He was concurrently a researcher at the Institute of Industrial Science (IIS), University of Tokyo,
from 1990 to 1994. He earned his doctorate (Dr. Eng.) in 1996 from the
University of Tokyo with the dissertation entitled “Numerical simulationof variable density flow with high buoyancy”. He has received three timesof the President of Maeda Corporation Prize Award for his outstanding
work in the field of Research & Development. His research interests
include computational and experimental wind engineering, urban ventilation, gas dispersion in cities, HVAC system utilizing natural energy (solar
energy and natural ventilation). Prof. Yoshie is the chairman of “WG for
prediction of ventilation and pollutant dispersion in urban areas” in theArchitectural Institute of Japan. He is also the chairman of “WG for windenvironment in cities” and the secretary of editorial committee in Japan
Association for Wind Engineering. He is one of the project leaders of the
Global COE Program: New Frontier of Education and Research in Wind
Engineering.

Masaaki OHBA
Masaaki OHBA is a professor of Architectural Engineering, Faculty of Engineering,Tokyo Polytechnic University since 1992.
He earned his B.Eng. in 1971 from Nihon
University and M. Eng. in 1974 from
National Yokohama University and D. Eng.
in 1978 from University of Tokyo. He
worked as a visiting scientist with chief
director W. Snyder at Fluid Modeling Division of US Environmental Protection Agency from 1992 to 1993. His
current research interests include cross-ventilation, digital imaging
technique and heat transfer phenomena in urban areas. At present, he isworking as a group leader for the Global COE Program : New Frontier of
Education and Research in Wind Engineering.

(Received 13 October 2009, Accepted 7 December 2009)