Regional atmospheric anomalies responsible for the 2009-2010 severe drought in China

The severe drought that emerged in summer 2009 and persisted in the subsequent fall and winter in southwest China caused a significant shortage of drinking and drainage water. Precipitation during the drought is much less than normal, and the meteorological drought extent exceeds the climatic mean in almost all the days during the period. The warmer-than-normal surface temperature facilitates the hydrological and agricultural drought through enhancing surface evaporation. The less-than-normal water vapor in the atmosphere and warmer-than-normal air temperature both contribute to the lower-than-normal relative humidity and thus the less-than-normal precipitation. The water vapor transport during the drought has no significant change in track but is much weaker in strength across the southwest. The weaker-than-normal water vapor transport and convergence in the fall and winter make it hard for the air to form heavy rains. The warmer-than-normal temperature corresponds to positive anomalies of geopotential thickness, with negative anomalies of geopotential height at lower levels but strong positive anomalies at middle and upper levels. The warmer-than-normal air temperature is important to the maintenance of the drought at this time of the year under the dry atmospheric condition. The persistent warm temperature makes it hard for the air to become saturated and thus hard for even light rains, which are efficient in mitigating drought, to form. The inherent mechanism in the atmosphere, namely, the positive feedback between less precipitation and warm temperature, helps maintain the drought.