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Kōka ( was a 弘化) Japanese era name ( after 年号, , literally "year name") nengō, and before Tenpō This period spanned the years from December 1844 through February 1848. Kaei. The reigning emperors were  Ninkō -tennō ( and 仁孝天皇) Kōmei -tennō (.
Change of era
December 2, 1844 ( Kōka gannen (): The new era name of 弘化元年) Kōka, meaning "Becoming Wide or Vast", was created to mark a fire at Edo Castle in Tenpō 15.
The nengo was not changed concurrent with the accession of Emperor Komei; instead, the Kōka era was retained until about a year after the new emperor was enthroned.
Events of the Kōka era
1847 ( Kōka 4): A major earthquake was recorded. 1848 ( Kōka 5): The last subscription noh of the premodern era. 
During these years, Hiroshige began making a series of prints showing beautiful women in contexts of famous places.
^ Nussbaum, Louis-Frédéric. (2005). "
Kōka" Japan Encyclopedia,, p. 546, at p. 546 Google Books; n.b., Louis-Frédéric is pseudonym of Louis-Frédéric Nussbaum, see Deutsche Nationalbibliothek Authority File Archived 2012-05-24 at Archive.today.
^ Keene, Donald. (2005).
Emperor of Japan: Meiji and his world, 1852-1912,, p. 101, at p. 101. Google Books
^ Rath, Eric C. (2006).
The Ethos of Noh: Actors And Their Art,, p. 218, at p. 218. Google Books
^ Oka, Isaburo. (1987).
Hiroshige: Japan's great landscape artist,, p. 87, at p. 87. Google Books