Indian summer monsoon (ISM), an important component of the South Asian climate system, has a great influence on the precipitation in Southwest China, especially Yunnan. An extremely weak or strong monsoon can have disastrous effects. An improved understanding of long-term variability in the ISM would thus be immensely beneficial. Pollen analysis of a 906-cm core taken from Lake Fuxian in central Yunnan was conducted to reconstruct vegetation and precipitation during the past 24 700 years in the lake catchment. Pine and evergreen broadleaved forests occupied the lake catchment during the last glacial period, when weak ISM brought less precipitation (with average MAP (mean annual precipitation) of 828 mm and precipitation of 693 mm in rainy season) to the basin. During the last deglaciation period, pine forests shrank and evergreen broadleaved forests expanded, indicating the intensification of the ISM and thus to bring more precipitation (average MAP of 965 mm and precipitation of 821 mm in rainy season) to the lake catchment. During the climate optimum period of the Holocene from 10300 to 4900 cal. yr. BP, vegetation was still dominated by pine and evergreen broadleaved forests, but the latter contained more tree species favoring warm and moist conditions such as Ulmus, Pterocarya and Liquidambar, implying the Holocene strongest monsoon as well as most monsoonal precipitation. At this period, average MAP and precipitation in rainy season were 1165 and 997 mm, about 355 and 327 mm higher than the present values, respectively. During the late Holocene from 4900 cal. yr. BP to present, vegetation was dominated by pines and herbs of Poaceae and Artemisia, reflecting a decreasing trend of precipitation due to weakening ISM. The average MAP and precipitation in rainy season at 4900 cal. yr. BP were 814 and 683 mm comparable with their modern observational values, implying that the modern ISM system has been established since then.
 

Indian Summer Monsoon; Lake Fuxian; Pollen; Vegetation; Mean annual precipitation; precipitation in rain season