Further Study of Yunnan Drought during the 2009/2010 Winter：Numerical Simulation of Impact of Antecedent Soil Moisture

The impact of anomalous antecedent soil moisture (in autumn) on the winter precipitation in Yunnan Province is investigated using the latest version of the mesoscale numerical model WRFv3.2. The simulated and analyzed results clearly show that the precipitation in Yunnan Province in winter (December 1-February 28) can be significantly reduced by unusually low antecedent soil moisture. The impact of the reduced antecedent soil moisture is so dramatic that the average reduction in precipitation is greater than 30% when the antecedent soil moisture is reduced to half that under normal conditions. In some regions, this number can even exceed 50%. Comparative analyses of the atmospheric circulation and major variable fields clearly indicate that a persistent northwest flow (dry air mass), an anomalous divergence, and the vertical velocity fields over Yunnan Province contribute directly to the reduced precipitation. By analyzing the precipitation events, the authors find that the precipitation intensity of every event is strongly influenced by the reduced antecedent soil moisture, whereas the frequency and timing of the precipitation events are affected less. This is related to the variability of physical processes in the atmosphere, including regional evaporation and thermal flux, that is caused by the reduced antecedent soil moisture. The simulation results of this study are consistent with previous results on the climatic impact of anomalous regional soil moisture.