Abstract:

Statistically collected historical flood records in different archives are analyzed to detect the flooding trend on a millennium scale in Hongze lake catchment，and floods responding to the climate change and its relationship with the El Nio events are identified.Results show that the frequency of the flood disaster has a generally upward trend in Hongze lake catchment，which suggests a good accordance to the trend of the climate change in the last millennium.During the periods of 1000~1400，records of flood are relatively lower，which reveals a direct response to the climate change during the Medieval Warm Period，in which an over 200 years drought period is detected.Similarly，during the periods of 1400~1800，records of floods are higher，demonstrating a close accordance to the climate change in the Little Ice Age from 1550 to 1850 which showed a relatively wetter environment in eastern China.Also，the contrasting relations between the floods and the El Nio events reveal that，big flood disasters are possible to occur in the year of the El Nio events and the year after the El Nio events in Hongze Lake catchment.The strength and location of the subtropical high in the western Pacific Ocean region and the changed atmospherical circulation caused by the El Nio events，which resulted in the abnormal excess precipitation in Hongze Lake catchment，can possibly serve as the physical mechanism of this phenomenon.Understanding this information may be of great help to flood mitigation and to effective decisionmaking for longterm flood management strategies in this area.

Key words: Hongze Lake/ flood/ climate change/ El Nio event