65

Relationship between Pollen Diseases andMeteorological Factors in Japan
Koji MURAYAMA1 and Michihiko TONOUCHI1*
1

Japan Meteorological Business Support Center
3-17 Kanda-Nishiki-cho, Chiyoda-ku, Tokyo 101-0054, Japane-mail: mu2@jmbsc.or.jp*corresponding author

Abstract
Pollen counts have been increasing and patients suffering from pollen allergy now exceed 14% of
the population of Japan. The amount of pollen has a positive relationship with the air temperatures andsolar radiation of the preceding summer. Using this relationship, pollen counts of the next season are
estimated roughly. According to the results of cedar flower observations in late autumn, the forecast is
made more accurate. The warmer spring is, the earlier the pollen season starts. However, a warm winterresults in a relatively late pollen season in the same regions of southern Japan, because warm wintersdisturb cedars’ dormancy. Cedar and cypress forests occupy 18% of Japan’s total land area. The pollencounts in 2050 are expected to be 1.6 times more and the number of patients to be 1.4 times than atpresent.
Key words: cedar pollen, cypress pollen, Japan, pollen allergy, pollen observation

1. Introduction
The ratio of patients suffering from cedar andcypress pollen allergies exceeds 14% of the population of Japan (Baba, 1997). Pollen observations werestarted in Sagamihara Kanagawa Pref. in 1965, andpollen counts have been increasing continuously
during the last 40 years (Fig. 1). In accordance with
the increasing number of pollen allergy patients,
pollen information such as actual pollen levels andshort-range pollen forecasts for each prefecture has
been made available since the 1980s. From theviewpoint of human health and medical care, springpollen information is the one of the most important of
the TV, radio, newspaper and IT services in Japan.
In Fig. 1, a typical Japanese cedar forest and flowers of cedar trees are shown.
In this report, we give an overview of knowledgeof the relationship between pollen and meteorologicalfactors. First, we introduce observation methods inJapan, second, we review the basic relationships between pollen counts and meteorological factors andfinally, in the last part of the present study, we discuss
future prospects for pollen problems.

2. Observation Methods of Pollen in JapanFirst, we review observation methods of pollen in
Global Environmental Research
11: 65-71 (2007)
printed in Japan

(a)

(b)

Fig. 1(a) A Japanese cedar forest
in Kashiwazaki, Niigata
Pref., in 2006.
(b) Male flowers of Japanesecedar in Kisarazu, Chiba
Pref., on Feb. 7, 2007.

Japan. Observation methods fall into two categories:
manual observation and automatic observation.
Manual observation methods include the ‘Durham
method,’ ‘Burcard method,’ ‘Rotary Durham method’©2007 AIRIES66

K. MURAYAMA and M. TONOUCHI

and others. These methods involve counting the number of pollen grains fallen or vacuumed on a plate, andthe most traditional observation method is the‘Durham method’ (Fig.2). At more than 100 observatories the pollen count at the site is obtained daily andreported through public web sites and other media.
These observatories have preserved historical datafrom the last ten years and this data is used for seasonal and short range forecasts. In order to observe
pollen by the ‘Durham method,’ we set a ‘Durham
stand’ outside. The stand consists of two circular
stainless steel plates to protect it from rain and direct
depression particles, and between these two plates, aslide glass holder. We installed a glass plate pasted
with white petrolatum, which fixes particles dropped
from the air, and changed the plate once a day around
9 a.m.
The recovered plates were stained with methyl violet (Fig. 2), and the pollen grains, (about 30 micrometers) fixed on the glass plate were counted using a
microscope. The pollen count at a site was the numberof pollen grains collected per 1 square centimeter area
during the observation period.
On the other hand, several automatic measuring
counters have been developed. Measurements are being made with these in some places and the pollencounts are reported through the Internet to the public.
A counter named the KH-3000 (produced by Yamato
Co. Ltd.), vacuums 4.1 liters of air per minute(Takahashi et al., 2001). When the air passes through
(a)

(b)

Fig. 2 (a) Durham stand and (b) cedar pollen.
(Sahashi, 2006)

its nozzle, the number of pollen grains is counted bylaser rays from two directions, the reflections of whichallow the instrument to distinguish the shapes andsizes of particles. In early spring, airborne sphericalparticles of about 30 micrometers in diameter are
mostly pollen, so the counter can determine theamount of pollen in the air. Another pollen counter,named the KP-1000 (Kowa Co. Ltd.) measurespolarized reflection from particles by ultraviolet laser
ray, and can distinguish types of pollen particles by
the ratio of Red/Green/Blue rays of reflection. Someother types of counters have been developed and are
in experimental use (Murayama, 2004).
The Ministry of the Environment started developing a pollen observation network called ‘Hanako’from 2003. The areas covered by the counters are
spreading year by year. By the spring of 2008, thenetwork will cover all of Japan. The hourly observation data are open to the public at the following website; http://kafun.taiki.go.jp/
Additionally, to enhance public awareness of pollen diseases, the Ministry of the Environment publishes and updates health guidelines for pollen diseases annually and provides the guidelines on their
web site; http://www.env.go.jp/chemi/anzen/kafun/html/
001.html

3. The Relationship between Pollen andMeteorological Factors
3.1 Seasonal pollen
Before a pollen season starts, patients wish toobtain predictions of (1) whether pollen counts in the
coming spring will be greater or lesser than averageand (2) when the season will start. To cure or ease
their symptoms, doctors should recommend theirpatients to start effective medical care two weeks
before the pollen season starts.
As is well known, the total pollen count in a year isaffected by the previous summer’s meteorologicalconditions. Cedar trees grow their male flowers,
female flowers and generative cells in the previous
summer. By photosynthesis cedar trees make nutrition
to promote growth of their flowers and cells, and if theduration of sunshine is shorter or the amount of solar
radiation is insufficient that season, cedar trees willconsume that nutrition to maintain themselves instead.
As a result, the number of flowers will become lessthan average and consequently the pollen count will
decrease the next spring.
Table 1(a) shows correlative factors between seasonal pollen counts and meteorological factors of theprevious July and August. Solar radiation has the mostpositive correlation with the pollen count of the next
season, and the maximum temperature, average airtemperature and duration of sunshine also have significant positive correlations. Precipitation and humidity have a negative relationship with the pollen countof the next season.

Relationship between Pollen Diseases and Meteorological Factors in Japan

67

In order to elucidate the appropriate periods affecting cedar pollen production, we calculated the correlative coefficients between the next season’s pollencounts and solar radiation for different periods asshown in Table 1 (b). The period with the strongest
relation to the next year’s pollen count, is the durationof sunshine from the first ten days of July to the firstten days of August. Data from shorter periods tends toshift more widely because of different tendencies
among different years, so to achieve reliable forecasts,
we adopted meteorological data of at least of 5 weeks
duration for forecasting seasonal amounts of pollen
particles.
Significant correlations with pollen counts of thenext season vary city to city. However, it can be concluded that generally the maximum air temperatureand solar radiation or duration of sunshine of theprevious summer are the best factors for predicting thenumbers of pollen particles in the next season.
As shown in Fig. 3, large amounts of solar radiation brought greater pollen counts the next spring, but
the condition of the cedar trees may also affect thisrelationship. For example, in the pollen seasons of1996 and 2003, the numbers of pollen particles decreased anomalously as compared to the generalrelationship. It is thought that when cedar trees
produce too much pollen, they cannot produce thesame level of pollen the next season. After great pollen dispersals, their production of pollen particles
tends to become smaller than would be estimated frommeteorological conditions.
In order to achieve more accurate forecasting, weapplied observation of cedar flowers in the lateautumn. Cedar trees stop producing their flowers bylate autumn, so by observing the numbers of cedar
flowers in autumn, we could adjust the pollen forecasts of the next season. Observation of the male
flowers is performed by evaluating cedar flowers ofeach tree in four categories. The cedar flower index inforests has a significant relationship with actual pollencounts (Kanazashi, 2003). By adding the results ofpollen flower observations and considering the average rate of increase of pollen particles, we improved
our pollen forecasts as shown in Fig. 4.

Table 1 Relationship between the pollen count of thenext season and meteorological factors of theprevious summer.

3.2 The first day of the pollen season
In Japan the first day of the pollen season is considered to be the first day with consequential pollen
dispersal, which is defined as having a pollen count of
more than 1 particle per square centimeter. Cedar male
flowers accomplish most of their growth by the previous November and go through diapause during winter.

(a)Meteorological factors

FactorAverage temperature
Maximum temperature
Humidity
Solar radiation
Sunshine duration
Precipitation

Correlative coefficient
0.78
0.78
–0.76
0.82
0.79
–0.32

(a)

8,000
7,000

(b)

Period6,000

Last dayFirst day
Jun 1
Jun 11
Jun 21
Jul 1
Jul 11
Jul 21
Aug 1
Aug 11Aug 21

Jun
10
0.1

Jun
20
0.08
0.12

5,000

Jun
30
0.15
0.15
0.18

Jul
10
0.22
0.28
0.34
0.34

Jul
20
0.25
0.51
0.61
0.62
0.48

Jul
31
0.51
0.55
0.71
0.74
0.74
0.51

Aug
10
0.48
0.61
0.72
0.83
0.68
0.64
0.32

Aug
20
0.41
0.51
0.58
0.72
0.61
0.52
0.31
0.29

Aug
31
0.33
0.37
0.49
0.66
0.49
0.48
0.32
0.27
0.21

Correlative coefficients between solar radiation at JMA in Tokyo, in
Chiyoda-ku, Tokyo, and subsequent year’s pollen counts observaed at
the Kanda Health Care Center, Chiyoda-ku, Tokyo.

Solar radiation

2,000
1,000
0
0

2,000

4,000

6,000

8,000

10,00012,000(b)

12,00010,000

6,000
4,000

10,000

2,000

8,000
6,000

3,000

8,000

grains / cm2
12,0004,000

0Pollen counts

0

2,000

4,000

6,000

8,000

10,00012,000

4,000
2,000
0

Fig. 3 The pollen count in a season and solar radiation of the previous summer.

Fig. 4 Improvement of estimations through pollen flower
research.
(a) With solar radiation only.
(b) With solar radiation and pollen flower observations.

68

K. MURAYAMA and M. TONOUCHI

After the cold days pass, their diapause becomeslighter. For example, in the Kanto area around Tokyo,
about 35 cold days are required before cedar trees
awaken from their diapause (Kanazashi & Yokoyama,
2002). After their winter dormancy, cedar trees start
preparing to flower. Once cedar trees awaken fromtheir dispause, basically the higher the temperaturerises, the sooner their flowers start to open.
Figure 5 shows the relationship between the timingof the first dispersal, in terms of number of days fromJanuary 1st, and the accumulated maximum temperature in 17 cities of the northern Tohoku area in 2002.
The relationship between the two factors is clear andthe first day of the pollen season can be estimated byweather forecasts. In cold areas, cedar trees sleep
enough during the cold winter, so the relationship isclear and forecasting is relatively easy. In warmer
areas, though, it is difficult to tell when cedar trees
will awaken from their diapause exactly, and the relationship between the first day of the pollen season andthe accumulated maximum air temperature is not clear.
As a result, forecasting is more difficult. Additionally,
if there is a cold spell or snow fall right before thecedar flowers bloom, the dispersal of pollen will shift
several days later than expected.
Figure 6 shows shifting of the ‘pollen front’ calculated from the average day of the first pollen observed
during ten seasons. The Japanese cedar pollen season
starts in early February along the Pacific coast andshifts northward. Finally the front arrives in southern
Hokkaido, the northern limit of natural cedar trees, atthe beginning of April. The cypress pollen season
starts in early March and arrives in Hokkaido in April.
According to the monthly average of maximum airtemperatures from 1997 to 2006, temperatures in
Kagoshima (12.9°C) are higher than in Oita (10.6°C),
but the average first pollen date from 1997 to 2006
was slightly later in Kagoshima (Feb. 12th) than in
Oita (Feb. 8th).
This is explained by the dormancy breaking theory.
Cedar flowers awaken and prepare for flowering after
cold weather. If cedar trees have not been exposed toenough cold air, they have been unable to sleep well,and the lack of dormancy makes the trees awaken later.
For this reason, the first day of the pollen seasons inwarmer Kagoshima is later than in Oita. It seems thatsuch delays began from the 1990s. In the same way,
the warmer December and January are, the later thepollen season starts.
3.3 Daily pollen dispersal
About one week after the first day of pollen dispersal, the daily cedar pollen count exceeds 10 particles.
Three or four weeks later, the pollen season reaches its
peak for the year. The cedar pollen season lasts about
two months in both eastern and western Japan.
Figure 7 shows daily pollen counts and maximum
temperatures in Tokyo in the spring of 2005. When itis (1) a fine warm day, the pollen count was relatively°C
Fig. 5 Accumulated maximum temperature from January
1st. and the first dispersal day from January.

(a)

(b)

Fig. 6 ‘Pollen fronts’ of (a) cedar and (b) cypress,
average of seasons from 1996 to 2005.
(F: February, M: March, A: April)

Pollen count (grains/day cm2)

Maximum Temperature (°C)

Fig. 7 Daily numbers of pollen particles and temperatures in Tokyo in March 2005.

Relationship between Pollen Diseases and Meteorological Factors in Japanlarge, but on (2) a day with low humidity and a strong
wind and/or (3) a day after rain has fallen, the numbers of pollen particles are much greater than usual.
The Pollen Information Standardization Committee (1995) reported that categories of daily pollen
levels have been set based on research on the relationship between the number of pollen particles observedby the ‘Durham Method’ and patients’ symptoms as
Table 2.
3.4 Hourly pollen dispersal
As mentioned above, lots of pollen floats in the air
on fine warm days. Figure 8 shows hourly pollencounts observed by the ‘Durham Method’ in Tokyo on
March 9th. 2003.
Depending on the weather conditions and location,a daily distribution of pollen with two peaks is normally observed on fine calm days. The first peak iscaused by a pollen run-off from cedar trees in mountainous areas. The distance from Tokyo to the main
cedar forests is around 50 to 70 km and it takes several hours for pollen to be transported from the forests
to the Tokyo area. The second peak is caused by thesubsidence of pollen floating in the air after sunset.
On the other hand, according to data from the automatic pollen counters, we found a third peak in theearly morning (Suzuki et al., 2005). It is thought thatpollen from the Izu Peninsula arrived after turning
toward the Kanto Plain or that, from northern forests,
pollen particles are transported separately by mountain breezes to the Tokyo area.

Table 2 The relationship between the number of pollen
particles and patients’ symptoms.
Patients’ symptoms(Category)
Low
MiddleHigh
CautionParticles (per day per 1 cm2)
less than 10 particles
10 to 29 particles
30 to 49 particles
more than 50 particles

Grains/hour cm2

69

4. Future Prospects for Pollen
As mentioned in the first section, pollen observations started in 1965, and the numbers of pollen particles during recent years have exceeded those of 1965
by a factor of two or three, as shown in Fig. 9.
The reason pollen has increased so rapidly can be
explained from two points of view: (1) cedar/cypress
forests themselves have been increasing because of
the decline of forest industries, leaving cedar/cypress
forests without any maintenance, resulting in diseases
and lots of untrimmed branches, (2) due to climatechange, the summer temperatures have become
warmer and the duration of sunshine has become
longer.
According to Forestry Agency’s reports (2002),
cedar and cypress forests have each increased by
100 million hectares from 1970 to 2000, and occupy
more than 18% of the entire land area of Japan (cedar
forests increased from 355 to 453 million hectares andcypress forest increased from 146 to 256 million hectares). The pollen production of cedar and cypress isknown to be at a prime when they’re in their middle
age, older than 30. Most Japanese cedar/cypress trees
grow up to such ages and younger trees are expected
to become adults for several decades. From this situation alone, the pollen count will be increasing every
year for a while. Additionally, ‘global warming’ helps
trees to produce more pollen. According to the Japan
Meteorological Agency’s reports (2005), the annual
average temperature has become 3°C higher during
the last 110 years (2005). In the next 100 years,
average temperatures will go up 3°C or 4°C higher
than at present.
The trends of recent meteorological factors inTokyo in July from 1987 to 2006 are that solar radiation has increased 19%, duration of sunshine has become 11% longer, average temperatures have become
1.7°C higher, and monthly precipitation has increased
by 24%.
As mentioned above, the duration of sunshine andair temperatures have a positive relationship to thepollen count of the next season, but increased precipitation affects cedar/cypress by inhibiting pollen
production. Recently, however, heavy rain of short
Grains/cm2

cedar/cypress pollen in Sagamihara

25,00020,00015,00010,000
5,000
0
Hours

Fig. 8 Hourly pollen dispersal at Tokyo on March 9,
2003.

1965

1970

1975

1980

1985

1990

1995

Fig. 9 Trends of pollen counts in Sagamihara,
Kanagawa Pref.
(Murayama, 2003)

2000

70

K. MURAYAMA and M. TONOUCHI

duration, as in tropical countries, has been increasing
and the number of rainy days has remained at thesame level, so it is difficult to conclude that more rain
will reduce pollen in the future.
Figure 8 shows future pollen counts in the case thatcedar/cypress forests increase and summers becomehotter. In the season of 2050, it can be estimated to be
1.6 times greater than in the season of 2000 if thetrend of the previous 20 years continues (Fig. 10(a)).
The number of patients visiting hospitals has astrong positive relationship to pollen counts. In Fig.
10 (b) shows the relationship between the number ofpatients visiting hospitals for the first time in their life
and the pollen count of the season. It reveals that thegreater the pollen count is, the more new patients start
to suffer from pollen allergies.
Medical doctors recognize this fact, and if the next
season’s pollen will be greater, they warn theirpatients and tell them how to prepare for the next pollen season, for example, to take pills earlier, to usemasks earlier than usual, to stay at home and so on.
Based on the increase in pollen calculated using
forest and climate data and the relationship between
numbers of pollen particles and new patients, we will
be able to estimate future trends in pollen allergy
patients as shown in Fig. 9(a). Pollen counts are
expected to be 1.6 times greater than at present.
The number of new patients should also increase by
1.4 times.

Pollenpatients

4,000

(a)

3,800
pollen

3,600
3,400
3,200
3,000

patients

2,800
2,600
2,400
2,200
2,000

Incidentally, ‘global warming’ makes autumn warmer, and warmer autumns affect the start of the nextpollen season, making it arrive later. Now the pollen
season in western Japan starts in the middle ofFebruary, but recently the first day of the pollen season has become later some of the time. On the other
hand in northern Japan, the first pollen dispersal day
has become earlier. It is thought that the beginning of
the pollen season in western Japan will gradually become later contrastively, while in eastern Japan, thefirst pollen dispersal day will become earlier at first,
but later in later years. Additionally, in recent years,
differences among individual forests have become
wider. This situation makes pollen forecasting moredifficult.

5. Discussion and Conclusion
Through more than 20 years of research, the relationship between pollen diseases and meteorologicalfactors has been elucidated greatly. However, the recent abnormal winter climate affects the beginning
day of the cedar pollen season. In the 2007 spring season, a new record was set for the first pollen dispersal
day in Tokyo on January 31. In western Japan inparticular, cypress pollen has been increasing rapidly
and as a result, the spring pollen season has become
longer. Cypress flowers grow not only in the previous
summer also in the early spring, in February andMarch, so it makes pollen forecasting more difficult.
However, information on the numbers of pollen
particles has been greatly developing. In the 2008
season, the network is going to cover all of Japan.
A numerical pollen prediction model has beendeveloped using past observation results. In the 2008
season, hourly pollen forecasts may be released
experimentally. With a variety of information, people
can easily check actual pollen counts and obtain futureforecasts. Such information will help patients to
reduce their risk of exposure to high concentrations ofpollen in the air and to ease their symptoms.

Year

Acknowledgements

1,800
Pollen

1,600
1,400

Finally we would like to express our gratitude to A.
Usami, N. Sahashi and all the members of the
non-profit organization Pollen Information Network
Japan.

(b)

1,200
1,000
800
600
400

References

200
Pollen (grains)

0
0

2,000

4,000

6,000

8,000

10,00012,000Fig. 10 (a) Trends in pollen counts and patients, (b)the relationship between pollen counts andpatients.
(Nishihata, 2004)

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