Abstract: Regional net precipitation variations may be evaluated using the hydrodynamic conditions and the fluctuations of the tropical maar lake level.In this paper,the magnetic fabric of sediments from two maar lakes,Shuangchiling(19°56.6'N,110°11.4'E)and Huguangyan(21°09'N,110°17'E)in tropical Southern China was studied to show the hydrodynamic variations of lakes since 9cal.kaB.P. The composite sediment profile ca.16m in length of Shuangchiling lake was compiled from a 16m-long core and a 8m deep well,and the profile ca.5m in length of Huguangyan Lake was obtained from three Livingstone piston cores collected in ca.10m water depth.Cubic plastic boxes(1.9×1.9×1.9cm3)were continuously sampled at ca.2cm intervals on two profiles to measure the anisotropy of magnetic susceptibility.The radio-carbon chronology of the Huguangyan profile was adjusted to the time scale of the Shuangchiling profile based on the paleosecular variation correlation between two lakes.The results show that the magnetic fabric properties of two lakes have the similar pattern and the consistent driving force.The minimum susceptibility axes(Kmin)are close to the vertical,perpendicular to the bedding plane,and tightly grouped,whereas the inclinations of the maximum axes(Kmax)are very shallow,indicating an original sedimentary magnetic fabric that has been undisturbed since deposition in weak hydrodynamic condition.The values of the anisotropy degree of susceptibility(P )of two lakes are all less than 1.08(with a mean value 1.023 in Shuangchiling Lake and 1.012 in Huguangyan Lake,respectively),and show a long-term up-section decreasing trend with three significant sub-stages in the intervals 9.0~5.6cal.kaB.P.,5.6~2.5cal.kaB.P.and posterior to 2.5cal.kaB.P.respectively,which agrees well with the oxygen isotope variations of the stalagmite and ENSO activities in the tropical area.This behavior,coupled with the increasing Non-AP(arboreal pollen)fraction,fining grain size and reducing organic carbon,demonstrates the declining process of lake hydrodynamic condition since ca.9cal.kaB.P.,although the low magnetic lineation(L )presents weak surface currents.The declining hydrodynamic condition should be resulted from the increasing net precipitation and rising lake level in tropical Southern China since the Early Holocene,which was mainly dominated by the southern shift of inter-tropical convergence zone(ITCZ)and strong activities of ENSO when the summer monsoon decreasing.The abrupt weakening of the hydrodynamic condition since ca.2.5cal.kaB.P.exhibits an environmental transition dominated by the net precipitation in tropical Southern China.