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

The long-term record of freezing dates of Lake Suwa in Central Japan since the 15th century are well-known among historical climatologists as valuable documentary data for winter climate reconstruction (e,g., Gray, 1974; Lamb, 1977; Mikami, 2008; Sharma et al., 2016). Recently, we newly discovered a long-term continuous record of lake freezing/breaking-up dates of Lake Jusan in Northern Japan during 1705-1860, which were described in the official diaries of the Hirosaki domain during the Tokugawa Edo Period.

Our previous studies of Lake Suwa freezing records indicate a strong correlation between freezing dates and winter temperatures, based on which we have attempted to reconstruct winter temperatures in Japan since the mid-15th century (e.g., Mikami, 2008).

Preliminary analysis for the 155-year time-series of the freezing and breaking-up dates since 1705 shows large year-to-year variations as well as long-term trends. Freezing dates were earliest around 1740 and latest around the 1820s. Breaking-up dates were earliest around 1720 and gradually became later through the 1830s. The duration of ice freezing at Lake Jusan shows no clear trend over the 155 years.

In addition, we compared freezing/breaking-up dates with simultaneous estimated air temperature in Tokyo. The result shows a highly negative correlation between breaking-up date and February air temperature in Tokyo. This suggests that air temperature in Tokyo corresponds to that at Lake Jusan, which might influence the thickness of lake ice. This in turn suggests that freezing/breaking-up dates for Lake Jusan might be useful in estimating winter climate conditions in Northern Japan, including Tokyo.

These results are compared with our previous reconstructions of winter climate based on Lake Suwa freezing records and daily weather records in old diaries since the 18th century.

References

Gray, B.M. (1974): Early Japanese winter temperatures. Weather, 29, 103-107.

Lamb, H.H. (1977): Climate, Present, Past and Future, Vol. 2. Methuen, London.

Mikami, T. (2008): Climatic variations in Japan reconstructed from historical documents. Weather, 63, 190-193.

Sharma, S., et al. (2016): Direct observations of ice seasonality reveal changes in climate over the past 320-570 years. Scientific Reports 6-25061.