Asian meteorological droughts on three time scales and different roles of sea surface temperature and soil moisture. (12th May 2021) - Zhang, Yanting
Abstract: The present study utilizes the standard precipitation index (SPI) to differentiate Asian summer droughts that are associated with variations of precipitation over periods of 3, 9 and 24 months (termed as short‐term, medium‐term and long‐term droughts, respectively). Then, the relationships between these droughts and atmospheric circulation, sea surface temperature (SST), and soil moisture are investigated. While the spatial and temporal characteristics of short‐term and medium‐term droughts are fairly similar, long‐term droughts display different spatial and temporal features. The leading spatial mode of short‐term and medium‐term droughts exhibits a dipole pattern with opposite loading north and south of approximately 30°N. The second spatial mode displays a tripole pattern with the same sign of loading over India and north‐northeast China–Mongolia and opposite loading in between. Temporal variations of short‐term and medium‐term droughts are dominated by interannual variabilities. For long‐term droughts, the first two spatial modes switch their order, and the long‐term trends are as important as the interannual and interdecadal variabilities. The droughts of the dipole mode are associated with SST anomalies featuring an El Niño‐like pattern in the tropical Indo‐Pacific Ocean that affect the drought variations through inducing large‐scale divergence and convergence. The interannual variability of the droughts with the dipole mode is also associated with the SST anomalies in the North Atlantic Ocean that affect the North Atlantic‐Eurasian atmospheric circulation. Local soil moisture conditions are more important for the formation of long‐term droughts than short‐term and medium‐term droughts. Abstract : The relationship of meteorological droughts measured by the standard precipitation index (SPI) to soil moisture differs for short‐term, medium‐term and long‐term droughts. The impact of precipitation on soil moisture tends to be larger than the impact of soil moisture on precipitation for short‐term droughts. The soil moisture–precipitation interactions are equally important for medium‐term droughts. The soil moisture plays an important role in the development of long‐term droughts.