Co-ching Chu (1890–1974), renowned Chinese meteorologist and former director of the Meteorological Institute, Academia Sinica, instructed assistants to transcribe Qingyu lu (lit. “records of clear weather and rain”) from the Palace Museum in Beijing in 1932, which was negotiated and assisted by Fu Ssu-nien (1896–1950), to study the historical changes in climate of the Beijing area. Qingyu lu records the times of rainfall, with the unit of time being every two hours, in several areas including Beijing, Nanjing, Suzhou, and Hangzhou in the Qing dynasty. Among them, the records pertaining to the Beijing area remarkably last from 1724–1903, a period of almost 180 years. In addition, Chu drilled into old pine and cypress trees around Beijing to measure their growth rings and further examine past amounts of precipitation. According to a letter from Chu to Fu, the former had Qingyu lu transcribed as he desired to compare the data with climate information recorded by geomagnetic observatories established in Russia. These observatories used one-hour units of time and recorded temperature, wind direction, and wind strength in addition to rainfall, data which was regarded by Chu as being of remarkable research value, especially concerning pre-Qing Beijing.
For more, see Co-ching Chu, “Weather Records of Pre-Qing Beijing,” Qixiang zazhi 2 (1936): 65–68 (in Chinese).