Informations on the cold weather and climatic disasters during part of the Little Ice Age for 17th to 18th Century in Japan were obtained from tree ring widths and some kinds of historical documents. Tree rings were analyzed both at Northeastern Japan (Fukushima Pref.) and Southwestern Japan (Okayama Pref.) mostly in Shinto Shrines' precincts. The daily weather records described in old personal documents such as diaries were inquired into at Hirosaki City (Aomori Pref.) for Fukushima's tree rings and at Tsuyama City (Okayama Pref.) for Okayama's tree rings. In this study, the snowy days' rate is used as an indicator of winter coldness. It is defined as the percentage of the number of days with snowfall to that with precipitation, that is, the total of rainy and snowy days. As a result, it could be concluded that the tree ring widths are narrower in the year of larger snowy days' rate. In Southwestern Japan, it is also considered that the drought summer as well as coldest winter caused the worse growth of trees.
In order to reconstruct the climate in a historical age, especially in the Little Ice Age, phenological data, such as the blossoming day of cherry, are available in a diary. The aim of this paper is to estimate monthly mean temperatures in March by the blossoming date of cherry flowers (Prunus yedoensis matsum) in Kakuson Nikki (Diary) at Kanazawa City and Shinkakuji Nikki (Diary) at Tosa City. Results were summarized in Table 1. Monthly mean temperature in the 19th century was lower by about 1°C than that for the present.
In order to reconstruct the march of climate before instrumental observations in Japan, Historical Weather Data Base has been constructed. Weather descriptions in historical documents, such as official diaries of Feudal Clans in Edo Era, or of local offices in each clan, are objects of the data base. Other descriptions are in those diaries of large temples, large shrines and large farmers, and in some of private diaries Considering the description of weather phenomena in old diaries, they were grouped into 13 weather conditions In this data base, “weather range” means weather conditions in a day. A rough tendency of the weather in a day (HN), or remarkable conditions such as hot, cold, dry and wet (HT), are also important to understand weather conditions for each day. Accompanied phenomena (TK) and wind conditions (KT, TT, KH) are also objects to encode. Daily weather records for the years from 1700 to 1889 are mainly under collections. So far, more than 2, 500 years weather records have been inputted in the daily data base. The main files of the system are PC-DA (paleo climatic data), and PC-REC (paleo climatic record). The former consists of encoded weather data which will be used chiefly to retrieve weather conditions and to draw maps or to make tables. The latter contains weather descriptions in each day with Katakana, one of the Japanese characters. This will support detailed investigation As an index of wet or dry condition for each month, “PI” is proposed. Weather conditions having some relations with precipitation are grouped to three kinds. Monthly frequencies of each type are multiplied by constants. These are 1 for “little rain”, 2 for “rain” and 5 for “much rain”. The total value in each month in each day is “PI”, which is useful for the comparison within the same daily series. The scatter diagrams of PI in Kokura Kita Kyushu City and Precipitation at Moji for each season are shown in Fig. 4. Time series of PI in 6 cities show the existence of different march in summer precipitations over Japan (Fig. 5). The monthly conditions in summer months from 1781 to 1789 are reconstructed in Fig. 6.
Many historical documents suggest that the climate of the Little Ice Age in Japan was cool and moist, especially in summer. Among these summers, the 1780s and 1830s might have been cooler and wetter, because severe famines due to the lack of rice production occurred frequently. The 1810s is also of great interest for the reason that this decade includes 1816 which is famous for the year without a summer in Western Europe and Eastern North America. An attempt was made to reconstruct summer temperature variations and variabilities during the Little Ice Age, especialy for the period 1771-1840, based on the daily weather records of old diaries in Japan. Comparison of summer temperatures and rainfall frequencies for the recent instrumental period reveals that they are closely related in terms of the causes for hot/cool summers over East Asia. In general, a hot and dry summer is brought by the continuous sunny weather conditiones under the influence of North Pacific High. By contrast, cool and wet summer is connected with the rainy weather conditiones caused by the passage of extratropical cyclones and polar fronts. By analyzing the correlations between the number of rainy days and the grid temperature data in August for recent years, linear regression equations were derived. Using these equations, August temperatures in Northeastern Japan and Central Japan were calculated. As a result, the 1770s, the early 1810s and the late 1830s were cool, on the other hand, the late 1790s and the late 1810s to the early 1820s were relatively warm. In Central Japan, the early 1810s and the late 1820s were somewhat cool. Reconstructed temperature series in Central Japan indicates large year-to-year variabilities for the whole period.
“The Little Ice Age” started in the 17th century and ended in the middleof the 19th century in Central Japan. The reconstruction of climatic conditions during the Little Ice Age was attempted, based on old documentary records. There are many old documents in which daily weather conditions were recorded. Those records were collected and arranged according to the order of dates. Through the works, weather diagrams were compiled for the historical times in Central Japan. By analyzing the diagrams, some climatic conditions during the historical times (from the end of the 18 th century to the middle of the 19 th century) were reconstructed for Central Japan. The main results are shown as follows. (1) Winter season temperatures were very low in the 1810's and the 1820's. After that it tended to become warmer gradually.(2) Precipitation amounts in winter on the Pacific coastal region is small. However after the 1830's, it increased to the present level.(3) Frequency of the appearance of the winter monsoonal flow pattern was higher in the 1810's and 1820's, and it became lower in the 1830's.(4) The end of the Bai-u season was delayed in the 1780's, 1830's and 1890's. In those periods, cool summers appeared in northern Japan frequently.(5) Heavy rainfalls frequently occurred during the Bai-u season in the middle of the 19th century. On the contrary, rainfall amounts during the Bai-u season were very small in the beginning of the 19th century.(6) In the beginning of the 19th cent ury, climatic condition of summer season was dry with little rain. Conversely, it is wet and much rain in the middle of the 19th century. There were some differences in climatic conditions between the early period and th e middle period of the 19th century. The main causes that bring these differences may have been the changes in general circulation patterns over East Asia. By comparing the climatic conditions in several different regions, the relationship between climatic changes andgeneral circulation patterns will be clarified.
Daily weather descriptions in diaries are examined to reconstruct the climate in “Little Ice Age”. Characteristics of weather terms, hours and precisions are clarified. Based on the examination, two indices, precipitation ratio in summer and snow ratio inwinter, are set up. Using many diaries, decadal distribution of indices are drawn and climate changefrom 1660's in Japan are reconstructed. The results are as follows. The summerswererelatively cool from 1730's to 1750's, 1780's, from 1830's to 1840's and 1860's. The winterswere relatively cold from 1680's to 1690's, 1730's and 1810's. However, climate change was notparallel between summer and winter.
In order to reconstruct the winter climate in Japan in the 18th century, the authors tried to gather weather records of old diaries written in that period. The winter climate in Japan is influenced by the east high-west low pressure pattern and its severity is highly correlated with the frequency of the pressure pattern on a seasonally or monthly time scale. The weather distribution pattern under the west high-east low pressure type is characterized by the bad weather in Japan Sea Coast and fine one in Pacific Coast. By the use of the character of the weather distribution pattern under the winter pressure, the frequencies of the typical winter days are interpreted from the weather distribution diagram made for the research period on a daily base from 1st November of the former year to the 31 st March of the year. The stations of the diaries gathered for the study are Hirosaki, Takada, Kanazawa, Sabae, Tottori and Hagi as Japan Sea Coast, Hachinohe, Morioka, Nikko, Kofu, Ise, Kyoto, Ikeda, Tsuyama and Usuki as inland or Pacific Coast. The results obtained from the study are shown in Figure 1 as an annual number of the frequency of winter pressure days. On the same time scale, the freezing dates and the records of unusual weather in winter (cold or mild) are composed in the figure. The relationsbetween the frequency and other historical documents are investigated. The secular changes of severity in winter were well coincided with the other weather proxies. The cold winter years can be found in the decades in the 1700s-1710s, the former 1730s, the 1750s and the former 1780s. The warmer winter years were in the decades in the 1720s, the 1740s, the 1770s, and the 1790s. Unusual severe winters recorded in the periods are not always identical to the frequency of the winter pressure days, because of its temporal or local effects.
Natural disasters in Little Ice Age (c. 1550-1850) and its climatic variations which formed a significant background for the disasters are mentioned. Cool summers due to a prevailing Okhotsk High were characteristic of this period. Cold winters, summer heavy rains and unstable atmospheric conditions also constituted essential features of Little Ice Age. Aerosol ejected by a series of major volcanic eruptions partly prevented solar radiation from reaching the earth' s surface (parasol effect), which resulted in cool and unusual weather. Agriculture, in particular, was vulnerable to bad weather damage. As a result of decreasing direct insolation, sometimes together with lowering temperature and/or locally increasing precipitation, seven major famines occurred during the Edo Era (1663-1868) which approximately coincided with Little Ice Age. Several cases in this paper suggest that natural environment in Little Ice Age was marked by both volcanism and weakened solar activities which “Maunder Minimum”(1645-1715) represented.