Analysis on Causes of Continuous Drought in Southwest China During 2009-2013
Severe droughts occurred in Southwest China continuously in 4 years’ autumn, winter, spring beginning from 2009. Because of the long duration, large scope and heavy degrees, the drought has caused huge economic losses, seriously impacting on agroforestry production and people’s life in arid zones. In this paper, the causes of the continuous drought are analyzed from the impacts of the anomalies of large scale atmospheric circulation, water vapor transportation, the Pacific and Indian Ocean SST, stratospheric polar vortex strength by analyzing a variety of data. The results show that the common backgrounds of the 4 years’ continuous drought are weaker south branch trough, less water vapor transport over the Bay of Bengal and easterly cold air mass caused by AO negative anomalies which are produced by abnormal wave activities during weak polar vortex. The abnormal changes of tropical SST during the drought over Southwest China play important roles in blocking water vapor transport over the Bay of Bengal and South China Sea. In the La Nina event, the effect of the tropical Indian Ocean SST changes in winter and spring is more outstanding. The phase of AO is always changed by the dynamic couple between stratosphere and troposphere in winter and spring, and the intensity and duration of the abnormally negative phase of AO have significant effects on the drought that occurred in Southwest China in the autumn, winter and spring of 4 consecutive years.