The rainy season in the Northwestern part of the East Asian Summer Monsoon in the 18th and 19th centuries

The Yu-Xue-Fen-Cun (YXFC) is one of the government archives of the Qing Dynasty (1644-1911) in China. It records the beginning/ending dates, duration and rainfall infiltration depths into soil and snowfall accumulation for individual precipitation event By comparing YXFC with instrumental data, a set of criteria used to identify the rainy season was established. This set of criteria was used to reconstruct the initial/final dates and length of rainy season during 1736-1900 and 1955-2000 at three sites (including Taiyuan, Datong and Yulin) based on both YXFC records and instrumental data. The results show that there is evident inter-decadal variation in rainy season length, with periodicity of 16-20a, 30-40a and 50-60a. The length of the rainy season gradually increases before the mid-19th century and decreases afterward, and the length of rainy season in 1736-1840 is statistically significantly longer than that in 1955-2000. These findings suggest that the intensity of the East Asian Summer Monsoon (EASM) became weaker from the mid-19th century, reaching the weakest condition in 1955-2000 during the context of the past 260 years. (C) 2010 Elsevier Ltd and INQUA. All rights reserved