Decrease in Extreme Precipitation in Summer over East Northern China and the Water-Vapor Transport Characteristics after Year 2000

In this study, the authors investigated the interdecadal change characteristics of the extreme precipitation (days of extreme precipitation: R95p; contribution rate of extreme precipitation: R95t) in summer in ENC (East northern China) during the period 1961-2016, as well as the differences in the atmospheric circulation and transport of water vapor for extreme and ordinary precipitation. The results show that both R95p and R95t have decreased significantly since 2000. Compared with the period 1984-1999, in 2000-2016, there were three circulation anomaly centers located in the Eurasian, Central Asian, and Northeast China-Mongolian areas, which exhibited a “positive-negative-positive” wavelike structure that caused a predominant and positive barotropic anomaly over ENC. A positive high geopotential anomaly with a sinking movement is unfavorable for the occurrence of extreme precipitation in ENC. The negative phase of the Pacific Decadal Oscillation (PDO) and the positive phase of the Atlantic Multidecadal Oscillation (AMO) have jointly reinforced positive anomalies in the geopotential height over ENC. The research results further reveal that there have been significant differences in the water-vapor transport and the key local circulation systems of extreme and ordinary precipitation events. Compared with ordinary precipitation, the water-vapor transport and budget for extreme precipitation from south to north were stronger. In addition, the ENC area was controlled by a stronger closed low-pressure system, which could have been enhanced by descending air with high potential vorticity during the occurrence of extreme precipitation.