 Seto Sea Climate
The Seto Inland Sea climate is one of the climate divisions
of Japan . It is also called the Seto Inland Sea climate ,
Seto Inland Sea type climate, or Setouchi climate . It is
mainly found in the Setouchi region.
Graphic - The yellow on the
map is the area affected by the Seto Inland Sea climate.
Click for a larger graphic
The Setouchi region is known for its moderate climate, with
a stable year-round temperature and relatively low rainfall
levels. |
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Insert Osaka Precipitation Map and
Other Pictures |
The summer monsoons are blocked by the Shikoku Mountains,
while the winter monsoons are blocked by the Chugoku
Mountains. As a result, the weather and humidity are stable
throughout the year, and precipitation peaks in May, June,
and July (the rainy season) and in September (autumn rains
and typhoons). The most notable feature is that
precipitation is extremely low in August (midsummer) between
the two peaks, which shows a large depression on the
rain-temperature chart.
The number of rainy days throughout the year (the number of
days when precipitation of 1mm or more is observed) is also
low, except during the rainy season (which includes
meteorological phenomena similar to the rainy season). This
differs from the situation in areas with a Pacific or Japan
Sea climate, where the number of rainy days increases or
decreases depending on the wind direction.
The amount of annual precipitation varies widely, and not
all areas are low-rainfall areas. Southern Okayama
Prefecture and Kagawa Prefecture have low precipitation
during the rainy season, at around 1,000 mm per year, making
them areas with low precipitation in Japan. In the Seto
Inland Sea region of the western Chugoku region, such as
western Hiroshima Prefecture and Yamaguchi Prefecture,
precipitation during the rainy season, when southwesterly
winds blow in from the Suo-Nada Sea and the Bungo Channel,
is higher than in other areas with a Seto Inland Sea climate. In addition, there
are a relatively large amount of rain
clouds introduced during the passage of low pressure systems
throughout the year, so the annual precipitation is around
1,600 mm, which is the average precipitation in Japan, and
reaches nearly 2,000 mm in mountainous areas. The Kinki
region, Ehime Prefecture, Fukuoka Prefecture, and the coast
of the Suo-Nada Sea in Oita Prefecture are intermediate
between these two. In addition, in the Kichu region of
Wakayama Prefecture, northern Tokushima Prefecture, and
southern Oita Prefecture, precipitation during the autumn
rainy season and when typhoons approach can be significantly
higher than in other areas with a Seto Inland Sea climate
and are treated as transitional
zones with the Pacific climate.
When there is little rain in the summer, drought damage can
occur. As a countermeasure, reservoirs have been built on
land adjacent to farmland since ancient times. Also, since
rain that falls on the mountains on the Pacific and Japan
Sea sides flows through rivers, water shortages can be
dealt with by building dams (such as the Yoshino River in
northern Tokushima Prefecture and Kagawa Prefecture) or by
using natural lakes and marshes upstream (such as Lake Biwa
in the Kinki region). Although the number of reservoirs is
decreasing due to residential development and improvements
in water utilization, there are still reservoirs of various
sizes (including those that have lost their original
purpose) in the Senshu region of Osaka Prefecture, the
Higashi -Harima region of Hyogo Prefecture, and Awaji Island. In addition, Kagawa Prefecture is known for having many
reservoirs because it has few mountains and often suffers
from water shortages. In particular, Okayama City in
Okayama Prefecture has adopted the slogan " Land of Sunshine
" because the number of days of precipitation has been the
lowest among prefectural capitals in the country since 1989
.
The climate is relatively warm, but in areas directly facing
the Sea of Japan or where the Chugoku Mountains are lower,
such as the Keichiku region of Fukuoka Prefecture, northern
Oita Prefecture, southern Yamaguchi Prefecture, and
western Ehime Prefecture, the number of days of
precipitation in winter is not as high as on the Sea of
Japan side due to the influence of northwesterly seasonal
winds, but is more than other areas on the Seto Inland Sea
side, and the characteristics of the climate on the Sea of
Japan side are somewhat seen. Also, around Hiroshima City
in southwestern Hiroshima Prefecture, which is at the foot
of the Chugoku Mountains, the number of days of snowfall in
winter is somewhat more than other coastal areas of the Seto
Inland Sea. In addition, in western Kagawa Prefecture and
eastern Ehime Prefecture (Shikoku Chuo City , etc.), the
hours of daylight in winter are short due to the influence
of seasonal winds that cross the Seto Inland Sea directly
from the Kanmon Straits and seasonal winds that pass through
the low-lying areas of the Gono River basin, and the climate
is similar to the Kyushu-type Pacific coast climate.
The amount of snowfall and number of snowy days is
relatively light along the Seto Inland Sea coast, but the
amount of snow is heavy along the mountains (especially the
Sanuki Mountains and Ishizuchi Mountains ), and many roads
become icy.
Additionally, northern Wakayama Prefecture, northern
Tokushima Prefecture, and central Oita Prefecture are on
the border (transition region) with a Nankai type Pacific
coastal climate; central Yamaguchi Prefecture, the Keichiku
region of Fukuoka Prefecture, and northern Oita Prefecture
are on the border with a Kyushu type Pacific coastal
climate; southern Kyoto Prefecture , northern Nara
Prefecture, southern Shiga Prefecture, and Iga in Mie
Prefecture are on the border with a Tokai type Pacific
coastal climate or a Central Highlands type inland climate;
and northern Harima and Tamba in Hyogo Prefecture, northern
Okayama Prefecture, and northern Hiroshima Prefecture are on
the border with a San'in type Sea of Japan coastal
climate.
Additional Climate Informaton
The Seto Inland Sea climate area has warmer temperatures and
less rainfall than the surrounding areas . The average
annual rainfall is between 1,000 and 1,600 mm. In
particular, during winter, the monthly sunshine hours are
about 1.5 times longer than in the Sanin region to the
north, separated by the Chugoku Mountains, and there are
areas with annual sunshine hours of over 2,000 hours.
The coastal winds are prone to land and sea breezes, and the
annual average wind direction is often perpendicular to the
coast. Also, the area is relatively unaffected by strong
winds blowing from the sky, and calms often occur when the
sea breezes and land breezes alternate. The evening calms
are famous, known as the "Evening Calm of Seto," and are a
factor that exacerbates the humidity in summer. However,
there are some areas where strong winds blowing down the
mountains are known to occur under certain weather
conditions, such as the Yamaji wind (near Shikokuchuo City).
Advection fog is common from March to June in the waters
from Bisan Seto to the Akinada, Hiuchi, and Iyo Seas . It is
common on sunny days covered by high pressure or when there
is a warm, humid current circulating around the high
pressure. |
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Regions with Seto Inland Sea climate
Due to topography and other factors, some areas in the
following regions exhibit other climates, and conversely,
some areas other than those listed below exhibit a Seto
Inland Sea climate. The backbone of the Chugoku Mountains in
northern Okayama Prefecture and southern Hiroshima
Prefecture are included in the Japan Sea climate. |
- Central Kinki
- Osaka Prefecture, southern Hyogo Prefecture, northern
Wakayama Prefecture (Kihoku)
- Sanyo
- Okayama Prefecture, Hiroshima Prefecture, central and
eastern Yamaguchi Prefecture
- Shikoku Seto
Inland Sea side - Kagawa Prefecture, northern
Tokushima Prefecture, Toyo and Chuyo Ehime Prefecture
- Kyushu Seto
Inland Sea side - Kitakyushu region of Fukuoka
Prefecture (Keitsu), northern and central Oita
Prefecture
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Climate Data
Areas with a definite Seto Inland Sea
climate
In the Seto Inland Sea area, the month with the most
rainfall is not during winter, and the month with the least
rainfall is during winter. The amount of precipitation outside of
the rainy season and autumn rains is low, even in midsummer. |
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Most precipitation days in a
month
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Minimum number of precipitation
days in a month
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Annual precipitation
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Most precipitation in a month
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Minimum monthly precipitation
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Rainfall in August
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Average annual sunshine hours
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Osaka
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11.2 (June)
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5.5 (December)
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1625.5mm
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209.5mm (June)
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62.3mm (January)
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130.9mm
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2013.1 hour
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Wakayama
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11.0 (June)
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5.2 (December)
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1316.9mm
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188.6mm (July)
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44.4mm (January)
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86.0mm
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2088.8 hours
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Kobe
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10.9 (June)
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4.7 (January)
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1216.2mm
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181.6mm (June)
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37.8mm (January)
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90.9mm
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1995.1 hour
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Himeji
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11.1 (June)
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4.6 (December)
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1199.0mm
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167.0mm (July)
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35.9mm (January)
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95.9mm
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2032.6 hours
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Sumoto
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11.5 (June)
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5.6 (December)
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1406.6mm
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200.8mm (June)
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45.6mm (January)
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106.9mm
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2066.8 hours
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Okayama
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10.4 (June)
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4.2 (December)
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1022.9mm
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161.5mm (June)
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31.0mm (December)
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87.4mm
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2102.3 hours
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Tamano
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10.7 (June)
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5.3 (December)
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1003.9mm
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145.1mm (June)
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30.8mm (December)
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74.8mm
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2288.4 hours
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Takamatsu
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10.3 (June)
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6.2 (December)
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1082.3mm
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150.6mm (June)
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37.3mm (December)
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85.8mm
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2053.9 hours
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Fukuyama
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10.2 (June)
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4.2 (December)
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1117.2mm
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176.7mm (July)
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31.0mm (December)
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83.0mm
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2096.1 hours
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Omishima Island
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11.1 (June)
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5.0 (December)
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1123.2mm
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180.6mm (June)
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37.0mm (December)
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74.4mm
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2009.8 hours
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Matsuyama
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11.5 (June)
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6.4 (December)
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1314.9mm
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223.6mm (June)
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46.0mm (December)
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89.6mm
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2017.1 hours
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Kure
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10.4 (June)
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4.2 (December)
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1381.3mm
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227.7mm (July)
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35.6mm (December)
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97.1mm
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2051.0 hours
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Hiroshima
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10.7 (June)
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4.9 (December)
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1537.6mm
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258.6mm (July)
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41.2mm (December)
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110.8mm
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2042.3 hours
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Transitional region with the Pacific
climate (Kyushu type)
The Seto Inland Sea region has the most rainy months in
summer and the least rainy months outside of winter, with
the amount of rainfall being particularly high from spring
through the rainy season. During winter, there is relatively
little sunshine and snowfall. |
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Most precipitation days in a
month
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Minimum number of precipitation
days in a month
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Annual precipitation
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Most precipitation in a month
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Minimum monthly precipitation
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Average annual sunshine hours
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Yamaguchi
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11.6 (June)
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6.2 (October)
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1886.5mm
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323.2mm (July)
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58.7mm (December)
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1894.8 hours
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Shimonoseki
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11.1 (June)
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6.2 (October)
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1684.3mm
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287.1mm (July)
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60.2mm (December)
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1880.5 hours
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Yawata
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12.4 (June)
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7.6 (October)
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1729.3mm
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299.9mm (July)
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68.0mm (December)
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1825.1 hours
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Transitional region with the Pacific
climate (Southern Sea type)
The Seto Inland Sea region has the most rainy days in summer
and the least during winter, and is affected to some extent by
seasonal winds from the south in summer and autumn.
Precipitation tends to be significantly higher when typhoons
hit, and the precipitation peaks do not show a clear bimodal
pattern between the rainy season and autumn rains. |
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Most precipitation days in a
month
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Minimum number of precipitation
days in a month
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Annual precipitation
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Most precipitation in a month
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Minimum monthly precipitation
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Rainfall in August
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Average annual sunshine hours
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Tokushima
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11.8 (June)
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4.6 (December)
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1453.8mm
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210.0mm (September)
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38.9mm (January)
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172.9mm
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2092.9 hours
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Oita
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12.0 (June)
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3.8 (December)
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1644.6mm
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273.8mm (June)
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34.4mm (December)
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172.2mm
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2001.8 hours
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Transitional region between the
Central Highlands climate and the Tokai-type Pacific coastal
climate
The months with the most rainy days are summer and the least
rainy are during winter, with little precipitation except during
the rainy season and autumn rains. Located in a basin and
inland, the area does not have many hours of sunshine and
experiences large temperature differences. Located near the
Sea of Japan, the area tends to have a slightly higher
number of snowy days and snowfall during winter, just like the
neighboring Nobi Plain . |
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Most precipitation days in a
month
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Minimum number of precipitation
days in a month
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Annual precipitation
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Most precipitation in a month
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Minimum monthly precipitation
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Rainfall in August
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Average annual sunshine hours
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Nara
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11.7 (June)
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6.1 (December)
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1316.0mm
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188.8mm (June)
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47.3mm (December)
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111.8mm
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1823.0 hours
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Ueno
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12.1 (June)
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6.3 (December)
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1363.9mm
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195.4mm (June)
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42.6mm (December)
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90.9mm
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1765.9 hours
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Otsu
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12.6 (June)
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7.1 (January)
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1529.7mm
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229.2mm (June)
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50.4mm (December)
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142.8mm
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1816.0 hours
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