Characteristics,cause factors and influence mechanism of flood and water logging in Shanghai

Based on the data including flood frequency,flood season rainfall,maximum tidal level and number of disappeared rivers during 1949-1991,considered the comprehensive affection of urbanization and regional environmental change on flood occurrence,this paper approaches the characteristics and change regulations of flood occurrence and flood-causing factors in Shanghai.The results showed that there have a downward trend of the flood frequency and an alleviatory trend of the flood extent in selected period in Shanghai.Flood control engineering efficiently decrease the occurrence and effect of floods.Changes of flood-causing factors well respond to the process of urbanization and regional environmental change.The flood causing way of each factor is different,rainfall and tidal level would affect flood occurrence and extent instantly and the impact of river disappearance on flood would lag 2-3 year and last for 4-5 years.Multiple regression analysis shows that the frequency trend of floods could be predicted by indicators of annual maximum tidal Level in Mishidu Station,the annual number of river disappearance and the flood season rainfall.