气候变化领域集成服务门户

Quantitative reconstruction of past precipitation for the monsoonal region in east-central China is of necessity in understanding East Asian Summer Monsoon (EASM) evolution. In this study, pollen-based quantitative reconstructions of the precipitation for Dajiuhu area since the late glacial period were produced by two appropriate approaches: Weighted Averaged Partial Least Squares (WAPLS) and Locally-Weighted Weighted-Averaging (LWWA). After numerical analysis, a modern pollen training set with a radius of 1000 km around the Dajiuhu Lake was established and two precipitation variables were selected for reconstruction. Mean Annual Precipitation (MAP) and Mean Summer Precipitation (MSP) reconstructed based on the two approaches had relatively high consistency (though the reconstructed value of LWWA is lower than that of WAPLS): (1) in the period of 16.0 ipitation was 10% lower than the mean value for the Holocene; (2) in the period of 10.0 cal ka BP - 7.0 cal ka BP, the precipitation reached an optima of the Holocene; (3) in the period of 7.0 cal ka BP - 4.0 cal ka BP, the precipitation was considerably lower than the mean of the Holocene; (4) in the period of 4.0 cal ka BP - present day, the precipitation fluctuated relatively drastically around the average line of the Holocene. The results indicated that the maximum intensity of the EASM in the data-covering period of the past similar to 16,000 years occurred in the early and middle Holocene, specifically from similar to 10.0 cal ka BP to similar to 7.0 cal ka BP. On the whole, our quantitative reconstruction results were highly coincident with the other proxy-based reconstructions of the changes in the East Asian monsoon. In the early and middle Holocene period when the monsoon was the strongest, synchronous changes in precipitation promoted regional expansion of mixed coniferous forests and broad-leaved forests. We preliminarily conclude that the periodic seasonal variation of longitudinal solar radiation gradient in summer at the low latitudes of the northern and southern hemispheres was the main controlling factor for precipitation in this region.