A southward migration of centennial scale variations of drought/flood in the eastern China and western U.S

Several studies of the established warm season climatic records for the eastern China (1470-1997) showed alternations of relatively dry and wet periods at centennial scales. The spatial patterns of these variations had such a structure that when a dry condition or drought was observed in the southern China a wet or flood situation was found in the northern part of eastern China and vice versa. These spatial variation patterns suggest a meridional propagation of the centennial scale wet/dry anomalies.

This study analyzed the same data and showed that the dry and wet anomalies initially appeared in the northern part of eastern China and then migrated southward to affect the low-latitudes. An extension of the analysis to the United States revealed a similar southward migration of dry/wet anomalies that first developed in the high latitudes in the western U.S. The average speed of the migrations in either of the two areas is about 3.0 degrees of latitude per 10 years.

The results suggest that mechanism(s) in mid- and high-latitude may play critical roles in developing droughts in high as well as subtropical latitude regions. They also pointed key areas to monitor for prediction of extended periods with frequent droughts or floods in "downstream" regions during the migration of the centennial scale anomalies.