Abstract:

Located north to the Yangtze River,the Poyang Lake is the largest freshwater lake of China.Extreme droughts have frequently occurred in the lake region in recent decade,and the droughts received increasing international attentions.From a perspective of basinscale water balance,this paper explored the processes and mechanisms of the frequently occurred droughts using longterm hydrologic data.The data include precipitation of the Poyang Lake Basin,outflow discharge of the Poyang Lake during 1960-2010,and evapotranspiration of the basin during 2000-2010.Our results demonstrated that the lake drought duration ranged from 1-6 months with a periodic cycle of 2-3 year and the duration tended to prolong with earlier starting dates and postponed ending dates.The frequently occurred lake droughts were resulted from the basinscale water deficits,among which the largest annual deficit was 343.6 mm for 2003,followed by 223.1 mm for 2007.The water deficits were mainly attributed to the deficiency in basinscale precipitation especially in 2003,2007 and 2009,and the increased evapotranspiration during 2000-2010,and the complex variation of outflow discharge within a specific year.At a monthly scale,precipitation anomaly showed a largest variation,followed by outflow discharge and evapotranspiration,demonstrating the dominance of meteorological droughts over hydrological droughts.In most cases,outflow discharge played a role secondary to precipitation in forming lake droughts,varying with the blocking effects of the Yangtze River.The blocking effects may enhance or lessen the lake droughts depending primarily on the water stage at the Hukou,the solely outlet of the lake water outflow to the Yangtze River.The water stage was relative lower than the multiyear mean by 0.46 m for 2001,0.94 m for 2004,1.64 m for 2006,1.29 m for 2007 and 1.22m for 2009,indicating the weakened blocking effects of the Yangtze River in the last decade.For an individual water year,substantial reduction of basinscale water income was principally responsible for the extreme lake droughts occurred in 2003,2004,2007,2008 and 2009,and the weakened blocking effects enhanced the water imbalance for the most cases.In general,the study provides an insightful view into the relationship of the meteorological and hydrological droughts,and the role of the Yangtze River in forming the droughts,which are valuable for effective promotion of climate adaptation and water resources management