Keywords: 
• sediment grain size /
• quasi-periodical /
• changes dry-humid transformation /
• Erhai Lake

Abstract: As a main lodging of surface substances, lake sediments continuously and sensitively record information of regional climate and environment with annual to decadal resolution. The sediment core EH911208-3-5 with a length of 83cm was taken from deepwater location in Erhai Lake in 1991, using the sediment-water interface sampler specially designed by ourselves. The sediments were cut at intervals of 0.5～1.0cm and were measured for grain sizes by the Scanning Photo Sedimentograph “Analysette 20” made in Germany. Based on accurate dating by ¹³⁷ Cs and ²¹⁰ Pb ex, the author reconstructs the dry-humid transformation history of the regional climate according to the vertical profile of sediment particle sizes, which provides a new effective way for recovering the century-scale climatic changes. The following conclusions are drawn: (1) General environmental significance of sediment grain size should not be applied mechanically in reconstructing palaeoclimate. Only after concretely analyzing all the factors which affect sediment grain size, can credible conclusions be obtained during discussing different time-scales climate changes. (2) During long time-scale studies, lake level is the most important factor dominating sediment grain size. Sediments are finer during the humid period of high water level because coarse particles can not be transported to the lake's deepwater part. On the contrary, during short time-scale studies within a given climate period, rainfall change in the drainage basin becomes the key factor determining sediment grain size because the lake level is basically constant. When rainfall is heavy, runoff flow is strong enough to bring coarse terrestrial particles to the sampling location, resulting in larger grain sizes. (3) The 15th century was the driest in the region of Lake Erhai during the past 640 years. There exist two time-scales(100 and 200 years) climatic quasi-periodical changes. From the end of the last century, the regional climate has been becoming drier and drier as a whole. At present, it is at the end of the dry period, so the regional climate will become humid in near future.