邕江洪水的特征及其气候成因研究

Characteristics and Climatic Causes of Flood in the Yongjiang River

利用邕江洪峰水位、年最高水位资料及邕江流域气象测站逐月降雨量资料,对邕江洪水的特征进行分析表明,洪水多数发生在华南后汛期7～9月,并与流域夏季降雨量密切相关。利用NCEP/NCAR再分析资料以及NOAA卫星观测的OLR资料,分析邕江洪水形成的天气气候条件,研究结果表明:热带气旋影响是邕江发生洪水的主要原因。当西太平洋副热带高压位置偏北,邕江流域易受热带辐合带(ITCZ)影响,对流活跃,热带气旋活动频繁,此时邕江易发生洪水;地形对邕江洪水的形成有较重要的作用;邕江洪水易发生在赤道东太平洋海温为负距平的条件下。分析了邕江洪水气候成因。

The analysis of the characteristics of flood in the Yongjiang River shows that the floods almost occur in July-September , the later rainy season in the southern China, and its variations correlate closely to the summer precipitation in the Yongjiang River drainage area by using the data sets of the flood peak and the annual highest water levels of the river, and the monthly precipitation over every observatory in the river drainage area. In this work, we analyse the climatic conditions causing flood in the Yongjiang River based on the NCEP/NCAR reanalysis data and the Outgoing Longwave Radiation （OLR） data. The results are as follows： （1） The flood in the Yongjiang River is mainly caused by Tropical Cyclones. When the West Pacific Subtropical Anticyclone is more northward than usual, ITCZ （intertropical convergence zone） can more easily affect the Yongjiang River drainage area, associating with the frequency of Tropical Cyclones and the activity of convection. （2） Landform makes an important contribution to the flood of the Yongjiang River. （3） The flood occurs easily in negative sea surface temperature anomalies （SSTA） over the eastern equatorical Pacific . We also analyse the variation of the synoptic systems cuasing the flood, and changes of the annual highest water levels in the condition of climate warming to futher realize the climatic reasons causing the flood.