Contribution of soil moisture-atmosphere coupling to summer droughts and floods over eastern China

Droughts and floods which occurred frequently in China, can have dramatic impacts on agriculture, water resources, ecosystems, and human welfare. Droughts and floods over China have been found to have an increasing trend over last several decades. However, our ability to predict droughts and floods remains poor, limiting our adequate society adaptation. Previous studies demonstrated that droughts and floods over China are associated with changes in East Asia summer monsoon (EASM), El Niño–Southern Oscillation (ENSO), changes in atmospheric circulation patterns, and global warming. An anomaly in soil moisture can alter latent heat flux and other surface energy balance components, and subsequently influence the climate at a variety of time and space scales. However, how soil moisture influences droughts and floods over East Asia is not yet well understood. In this study, we investigate soil moisture feedbacks on summer droughts and floods over eastern China for the 1998 and 1999 cases using the Weather Research and Forecasting (WRF) model simulations. Soil moisture climatology, derived from a 20-year-long control run, is used to replace soil moisture evolution in uncoupled simulations for 1998 and 1999 summers. Eastern China experienced severe floods during the summer of 1998, while 1999 summer is characterized by a “southern flood and northern drought” pattern. The WRF model generally simulated precipitation anomalies relatively well in both the magnitude and spatial pattern in the two summers though some biases remain. It is found that soil moisture-atmosphere coupling contributes substantially to both droughts and floods over northern China while it plays a relatively small role in precipitation anomalies over southern China. Our findings suggest that soil moisture memory help contribute skill to seasonal prediction of droughts and floods over northern China.