十八世纪我国长江下游等地区的气候

A STUDY ON THE CLIMATE OF THE 18TH CENTURY OF THE LOWER CHANGJIANG VALLEY IN CHINA

关于1500—1900年小冰期气候问题是历史时期气候变化研究中的一个重要课题。本文根据我国晴雨录、古代天气日记、诗文等历史文献资料来讨论小冰期中一个相对温暖时期(十八世纪)的气候。研究表明,这个时期冬季(12—2月)平均气温比现在低1.0℃(杭州、苏州)到1.5℃(南京)。但其间还有10年以上时间尺度的起伏波动,在温暖时段,冬季平均气温仍比现在低0.5—1.6℃,在寒冷时段,冬季平均气温比现在低2.1—2.4℃。但十八世纪大部分时期春季反比现在暖些。对湿润状况分析表明,十八世纪长江中下游地区比现代潮湿,反映了当时大气环流与今有较大差别。杭州古风向记录(1723—1769年)分析表明,当时盛行风向与现在不同:冬季西北风频率比现在多,春秋盛行东北风时间比现在长,频率比现在多。

A variety of data from ancient documents and diaries provides a more detailed picture of climate of the 18th century. The best continuous records of climate over that period come from "weather diary" , in which clear sky and duration of rain (snow) were recorded daily during the first half of the 18th century, which were observed by the officers of Hangzbou, Suzhou, Nanjing and Beijing by the order of the emperor.In the temperature derived from the above mentioned records, the ratio of snow and precipitation has been adopted to eliminate the effects of moisture conditions. Regression equations between this ratio and the temperature of Hang-zhou, Suzhou and Nanjing have been developed on the data of the last 30 years and thus temperature for the early 18th century has been obtained. It shows that the ratio of snow and precipitation days in the 20 s to 70 s in 18th century was 10-15% higher than that of today,and the derived temperature was 1℃ (Hangzhou and Suzhou) and 1.5℃ (Nanjing) lower than that of today. The 18th century was known as a warm period within the little ice age, but this paper shows that even in this warm period the temperature was lower,The groups of warm and cold years are given in table 3.The second item discussed is the phenomena in spring,Based upon the personal diaries of the 18th century, the blooming dates of Malus micromalus Makino and Prunus persica (L) Batsch are collected in table 6 .In average, the blooming date in the 18th century was 6 days later than that of today and it could be estimated that the climatic belt has moved southward by 1.5 degress in latitude.Winds were observed daily in 8 directions from 1723-1769 and are compiled in table 7 ,It was obviously different from today’s records,From November to January, the frequency of northwest wind was 10% less than that of today, and from February to October, the prevailing wind was northeast in the 18th century, but now, only in two (September and October) months northesterly prevails.By the present weather knowledge, we know that the prevailing northeast wind is often accompanied by wet wealher in the lower Changjiang valley.Based on the reports of the local histories, the deviation of index of moisture conditions of the 18th century is given in figure 3 (taking the present regime as normal) .The wet weather in the lower Changjiang valley supports the result mentioned above.Thus it is possible to argue that the climatic history of the 18th century from different sources summarized above exhibits a good deal of agreement with the reality of climatic pattern.