Hydroclimatological influences on recently increased droughts in China'slargest freshwater lake

摘要

Lake droughts are the consequence of climatic, hydrologic and anthropogenicinfluences. Quantification of droughts and estimation of the contributionsfrom the individual factors are essential for understanding drought featuresand their causation structure. This is also important for policymakers tomake effective adaption decisions, especially under changing climate. Thisstudy examines Poyang Lake, China's largest freshwater lake, which has beenundergoing drastic hydrological alternation in the past decade.Standardized lake stage is used to identify and quantify the lake droughts,and hydroclimatic contributions are determined with a water budget analysis,in which absolute deficiency is defined in reference to normal hydrologicconditions. Our analyses demonstrate that in the past decade the lakedroughts worsened in terms of duration, frequency, intensity and severity.Hydroclimatic contributions to each individual drought varied betweendroughts, and the overall contribution to the lake droughts in the past decade came from decreased inflow, increased outflow, and reducedprecipitation and increased evapotranspiration in the lake region. Thedecreased inflow resulted mainly from reduced precipitation and less fromincreased evapotranspiration over the Poyang Lake basin. The increasedoutflow was attributable to the weakened blocking effects of the YangtzeRiver, which the Three Gorges Dam (TGD) established upstream. The TGDimpoundments were not responsible for the increased number of droughtevents, but they may have intensified the droughts and changed the frequencyof classified droughts. However, the TGD contribution is limited incomparison with hydroclimatic influences. Hence, the recently increaseddroughts were due to hydroclimatic effects, with a less important contributionfrom anthropogenic influences.