18世纪南京、苏州和杭州年、季降水量序列的复原研究

RECONSTRUCTION OF ANNUAL AND SEASONAL PRECIPITATION SERIES OF NANJING, SUZHOU AND HANGZHOU DURING THE 18^(TH) CENTURY

利用清代宫廷档案“晴雨录”南京、苏州和杭州的逐日天气记录,复原了 18世纪三地的年、季和月降水量序列;论述了将“晴雨录”的逐日降水时数和降水类型的记载转换成 7级降水日数和逐步回归推算月降水量的方法及其科学依据;给出长江下游地区 18世纪典型多雨、少雨年份的降水量值。18世纪南京等三地的年、季、月降水量序列的复原,对了解在寒冷小冰期中相对温暖时段我国主要农业区长江三角洲地区的降水特征有重要意义。

The Qing Dynasty Royal Archive “Clear and Rain Records” (CRR) are daily weather reports collected from all the country, of which only those at Beijing (1724～1903), Nanjing (1723～1798), Suzhou (1736～1806), and Hangzhou (1723～1773) can be used to reconstruct climate series. The precipitation series on an annual, a seasonal, and a monthly basis have been re-established for Beijing but it is more difficult to reconstruct precipitation series for Nanjing, Suzhou and Hangzhou (denoted as the target regions hereinafter) because of the lack of corresponding instrumental measurements except for textual description. The author has attempted to reconstruct summer monthly precipitation series for the target regions, leaving the re-establishment of their yearly sequences unfinished. Based on the inference for the summer monthly rainfall a system for stepwise regressions of 8 factors is formulated using modern precipitation data in conjunction with preprocessing procedures done for the information from the CRR. This method made the transformation of multiple precipitation patterns, i.e., precipitation intensities for some duration(hrs) on the same day into the number of hours for the same precipitating pattern, thereby allowing to quantitatively calculate annual precipitation for the target regions. The developed scheme has its key kink in how to get daily levels of the amount of precipitation from CRR-given heavy, light and drizzle rain with the duration, and the conversion is based upon the principle stating that monthly numbers of rainy(snowy) days leveled by 7 categories are in better relative proportions which remain much the same in 1951～1970 and 1971～1990. By setting the feature, i.e., the long-term mean numbers of rainy (snowy) days in relative proportion, to be valid in the 18 th century, we are allowed to make conversion in the following way that the durations are combined with rainfall(snowfall) patterns shown in the CRR on a monthly and local basis to produce 5~7 combinations, each of which having the numbers of rainy days for a rainfall pattern in relative proportion, analogous to those discovered in modern climatology. In this way, each combination is related to one level of rainfall amount only. After the transformation we get a plot of multi-yearly mean numbers of monthly rainy(snowy) days in relative proportion for amount-levels for the target regions. This work presents the curves of annual total and May～September rainfalls for the target regions, with total of typically rain-rich years (1730, 1741,1767 and 1769), rain-deficient years (1723, 1748 and 1751) given (maximizing at 1 926mm and minimizing at 580mm on a yearly basis). These results are comparable with those obtained from studies on early-stage Meiyu(plum rains) activity for the 18 th century. It is worth noting that the CRR rainfall events for the target regions occurred in a relatively warm phase of the Little Ice Age in the 18 th century so that the reconstructed yearly and seasonal precipitation sequences are of usefulness to the understanding of rainfall features and the assessment of climate variation for the Yangtze Delta region as one of the primary agricultural regions of China in the warm climate background.