Rapid increase in extreme snowfall events over the last 40 years in Northeast China

Based on the station observations and reanalysis data, this study investigates the temporal variation characteristics of winter extreme snowfall events over Northeast China (NEC) and the possible causes involved. In recent four decades, the snowfall amount over NEC has a significant increasing trend, especially during the 21st century, which is dominated by its extreme component. On the contrary, the snowfall days over NEC exhibit an opposite variation trend, showing a rapid decrease during the research period. The opposite variation trends suggest a rapid increase of extreme snowfall events in this region. Composite results of 39 extreme snowfall cases reveal that the dominant circulation pattern causing the extreme events is the enhanced local meridional circulation over the north NEC, and significant relationships can be found between the northeast cold vortex (NECV) and extreme snowfall event. During the 21st century, both the 500 hPa geopotential height and the 850 hPa air temperature present negative tendencies over the middle and high latitudes of Asian continent. This is beneficial for stronger and more frequent northerly winds behind NECV to cause more intensified low-level convergence over this region and finally trigger more extreme snowfall events.