Long-term winter/spring climatic changes in Northern Japan reconstructed from snowfall rates and lake-freezing records

In Japan, numerous official diaries of local domains, which include daily weather records, are a useful tool for reconstructing climatic changes from the 1660s to the 1860s. Especially in winter, Japan has much snowfall on the western Japan Sea side, where snowfall rates (snowfall-days/precipitation-days) are presumably a good indicator of winter severity. Accordingly, we calculated correlation coefficients of snowfall rates and winter/spring mean temperatures at Hirosaki in Northern Japan using meteorological data from 1983-2020. The results show a statistically significant correlation (r=0.66), which suggests the possibility of estimating winter/spring temperatures in historical times based on continuous long-term records of snowfall rates derived from local diaries.

As reported in Hasegawa, et al. (2020), we newly discovered a long-term record of the freezing/breaking-up dates of Lake Jusan in Northern Japan during 1705-1860, which provides valuable information on winter/spring climatic changes. Therefore, it would be possible to estimate winter/spring temperatures if there exists a strong correlation between freezing/breaking-up dates and winter/spring mean temperatures in actual instrumental observations since the 20th century. However, lake freezing records are not available after the 1860s, so instead we compare the timeseries of Lake Jusan ice freezing durations and snowfall rates at Hirosaki in Northern Japan on the basis of local official diaries. As a result, both timeseries show relatively similar variations during the period 1705-1860. We plan to reconstruct winter/spring climatic changes in Northern Japan from the 18th century to the present by combining both proxy and meteorological data.

References Hasegawa, N., Mikami, T., Hirano, J. and Batten, B. (2020):Newly discovered long-term record of freezing/breaking-up dates of Lake Jusan in Northern Japan during 1705-1860 as compared with those of Lake Suwa. AGU Fall Meeting, 2020.