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This study analyzed precipitation data during the 1860s in Yokohama, Japan, using observations made by an American Christian missionary, J.C. Hepburn. Hepburn's meteorological data included monthly maximum, mean, and minimum temperatures, monthly precipitation, and the number of rain days in each month. The climate during the late 1860s was characterized by large inter-annual precipitation variability during summer. We detected unusually heavy rainfall during the summer of 1868, whereas the summer of 1867 was characterized by extremely low precipitation. These trends are in accordance with precipitation patterns reconstructed from historical weather documents. Furthermore, we investigated the spatial distribution of extreme climate events in 1867 and 1868 throughout Japan. The results suggest that the unusual dryness in 1867 and wetness in 1868 were related to synoptic-scale climate in Japan, rather than local-scale patterns in Yokohama. The results from this study could be used to understand the nature of summer climate variations in Japan in the 1860s.

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