Abstract
In the present study, we estimated the July maximum temperature variations from 1830 to 2011 in the town of Kawanishi in the southern part of Yamagata prefecture using daily weather reports and observations documented in an old personal diary. Using historical weather reports, we computed the number of “fine-weather” days for each July during the study period. Then, July maximum temperatures in Kawanishi were estimated using a simple linear regression analysis based on the relationship between the July maximum temperature and number of “fine-weather” days, computed from historical weather reports. By comparing the time series of estimated temperatures with those of historical instrumental temperature data in the late 19th century, we found that the variation in the estimated temperature correlated well with that of the instrumental temperature data. This indicates that the estimated results in the present study are highly reliable. The results of this analysis showed that there were cool periods in the 1830s, 1860s, 1900s, and a period extending from the 1980s to the early 1990s. Those cool periods in the 1830s, 1860s, and 1900s coincided with poor rice harvests and severe famines in northern Japan. Warm summers were observed in the 1850s, a period extending from the 1870s to 1880s, and 1920s. We found that temperatures in the early 1850s were similar to those of warm summers in the late 20th century.
