Abstract:

 Based on observed precipitation and the NCEP/NCAR reanalyzed datasets from 1980 to 2011, possible causes of abrupt turning from drought to flooding in the middle and lower reaches of Yangtze River valley (YRV) region during spring to early summer of 2011 were discussed using methods of an EOF and a linear regression analysis. The results indicate that the persistent La Nina events during January to May of 2011 maintain the 125°E eastward shift of western North Pacific subtropical high (WNPSH), thus the southwesterly moisture flux fails to reach the YRV region, which leads to the persistent drought events from January to May of 2011. However, sensitive heating flux enhances in the Tibetan Plateau (TP) with the decaying of La Nina in June, which induces a westward shift of WNPSH moving to 110°E from east to northwest and makes water vapor from southwesterly wind transporting to the YRV. Convection from the TP enhances and moves to east, and it meets southwest air flow from the northwest side of WNPSH in the middle and lower reaches of the YRV, which leads to increase precipitation sharply, and then it forms abrupt turning from drought to flooding in 2011.

Key words: Abrupt drought and flooding turn, La Nina, Sensitive heating