EFFECT OF SEASONAL CIRCUMFLUENCE DRESSAL IN SPRING AND AUTUMN ON SUMMER FLOOD IN HUBEI PROVINCE

Flood is the major meteorological disaster of Hubei Province. Nine lasting torrential rain flood year are defined after analysis on climatic characteristics of precipitation in the flood period in Hubei Province, which occur mainly in years when there is a southern or middle raintype in the eastern China. The correlation between the rainfall in the eastern Hubei in the flood period and 500 hPa circumfluence elevation field is analyzed. It concludes that abnormal redressal of circumfluence in spring and autumn is an important prophase factor in forecasting rainfall in the flood period in Hubei Province. A departure composing demonstrates that, in typical flood year and draught year, the departure from average of the heights at 55°—65°N in preceding March is inverse within 130°E—120°W and 90°—10°W. The 500 hPa circumfluence fields of preceding March of the year and March, October of the year before are studied to find out some key indexes which make senses on the abnormal excessive summer rain in the Province. Then a short-term climatic forecasting model for summer flooding year in the Province is established. The model utilizes two factors to transfer serious flood as a small probability (probability=18%) occurrence into a big probability (probability=70%) occurrence, after that, a judgment is made through two steps, which demonstrates a 100% distinguishing rate for the serious flooding year in history of Hubei Province, and the test forecast for 2000—2002 accorded well with actual conditions.