Enhanced moisture transport associated with the interdecadal change in winter precipitation over Northwest China

In this study, the interdecadal increase in winter precipitation in northwest China (NWC) since the late 1980s and the associated moisture flux transport are investigated. The results show that an interdecadal change in moisture flux transport also occurred in the late 1980s, resulting in anomalous moisture transport convergence over NWC. The examination of boundary moisture transport shows enhanced incoming net moisture flux transport over NWC after the late 1980s. The zonal and meridional components both play a key role in the net moisture flux transport, with increased incoming transport from the western boundary dominated and followed by increased incoming transport from the southern boundary. The circulation responsible for the moisture flux transport anomalies is a Eurasian (EU)-like teleconnection over mid-to-high latitudes of the Eurasian continent. The EU teleconnection pattern transformed from a positive phase to a negative phase in the late 1980s. The related anomalous cyclone over central Asia and the anomalous anticyclone over Japan result in westerly anomalies to the west of NWC and southeasterly anomalies to the east, respectively. Together, these anomalies enable an enhanced net gain of moisture transport and the anomalous moisture transport convergence over NWC. The enhanced moisture supply, strengthened upward movement and anomalous convergence result in an interdecadal increase in winter precipitation in NWC. In addition, the transition of the EU teleconnection is likely attributed to changes in the zonal mean wind. Sea surface temperature warming in the North Atlantic and northwestern Pacific regions also play a role in the change in the EU teleconnection pattern.