Meteorological and Hydrological Characteristics of Flood Related Torrential Rain over Huaihe River Basin in 2007

Based on the regular meteorological and hydrological data during the Huaihe River Basin torrential rain in 2007, the torrential rainfall process, the related large scale atmospheric circulation pattern and the evolvement of the flood as the meteorological and hydrological characteristics are analyzed. The conclusion hereby is drawn for the cause of flood happening by the torrential rainfall. The conclusion shows that the Huaihe River Basin flood is mainly related with seven torrential rainfalls. The later four torrential rainfalls are recognized as the significant factor to bring the Huaihe River Basin flood which happen during June 29 to July 10. Although the former three torrential rainfalls are not strong and not recognized as the main cause of flood, the water increase is still led to and becomes the hidden trouble of the whole valley heavy flooding, because the present of precipitation center is mainly in the northern Huaihe Basin where the anabranch of Huaihe is densely located. The large scale atmospheric circulation pattern shows that the torrential rain in Huaihe River Basin occurs under the quite typical Meiyu situation, and the stability of subtropical high has a great impact on the establishment of strong rain-belt. The hydrological data analysis reveals that the higher water line as well as the less water fluxes is on the upriver of Huaihe River Basin which is associated with the severe flood. The increase of the water level is directly led to by the heavy rainfall in the main Huaihe River Basin, and the variable of the water level is associated with the heavy rainfall especially in the upriver of Huaihe River. The rapid increase of the water level of Wangjia-dam is resultedin by the heavy rainfall in the upriver of Huaihe River Basin 2 days later, then the water level of Wangjia-dam exceeds the dangerous level after 2 phases rapidly increase. Based on the comparison and analysis with historical flood year of Huaihe River Basin, the result shows that the accumulated precipitation during the period of Meiyu in Huaihe River Basin in 2007 is the fourth heaviest in history, which is only less than the flood year of 1954, 1991 and 2003. Nevertheless, the water level in the main Huaihe River Basin is higher than that in 1991 and 2003, which is the second in historical record since 1954.The water level of Wangjia-dam is associated with the area rainfall of Wangjia-dam-Dapoling and Dabie-mountain valleys. The high water level of Wangjia-dam is caused by the heavy rainfall in the upriver of the Huaihe River Basin, which reflects the hydrological characteristics caused by the special geographical condition: The rainfall in the upriver is the main factor to bring the high water level in the main Huaihe River Basin.