Kosai is located in the far southwest corner of Shizuoka Prefecture, bordered by Aichi Prefecture to the west, Lake Hamana to the east. The name of the city means "west of the lake", in reference to its location near Lake Hamana. The city is bordered to the south by the Enshū Gulf of Pacific Ocean. Due to its location, the warm Kuroshio Current offshore provides for a temperate maritime climate with hot, humid summers and mild, cool winters.
Neighboring municipalities
Shizuoka Prefecture
Hamamatsu
Aichi Prefecture
Toyohashi
Demographics
Per Japanese census data, the population of Kosau has been relatively steady over the past 30 years.
Climate
The city has a climate characterized by characterized by hot and humid summers, and relatively mild winters. The average annual temperature in Kosai is 16.0 °C. The average annual rainfall is 1942 mm with September as the wettest month. The temperatures are highest on average in August, at around 27.3 °C, and lowest in January, at around 5.5 °C.
History
The area around Kosai has been noted for the production of Japanese pottery and porcelain since the Kofun period. During the Edo period, Kosai was tenryō territory administered directly by the Tokugawa shogunate, and the location of a barrier gate regulating traffic on the old Tōkaidō highway connecting Edo with Kyoto. A post station named Shirasuka-juku developed near the barrier, and this was the forerunner of modern Kosai. During the establishment of the modern municipalities system of the early Meiji period in 1889, the area was reorganized into five villages within Hamana District, Shizuoka. Four of these villages merged to form the city of Kosai on January 1, 1972. On March 23, 2010, the town of Arai was merged into Kosai. Hamana District was dissolved as a result of this merger.
Government
Kosai has a mayor-councilform of government with a directly elected mayor and a unicameral city legislature of 18 members. The city contributes one member to the Shizuoka Prefectural Assembly.
Economy
The economy of Kosai is dominated by light manufacturing of automobile components and electronics, as well as commercial fishing. Kosai is home to Suzuki Motor Corporation's Kosai Assembly Plant, Suzuki's main domestic production plant as well as to plants owned by Panasonic and Sony. Commercial fishing and aquaculture on Lake Hamana is also a component of the city's economy.
