Evaluating How Historical Climate Change Affected a Heavy Snowfall Event in Northern Japan in Mid-December 2021 Using Two Pseudo Global Warming Methods

Abstract

In mid-December 2021, heavy snowfall occurred when an extratropical cyclone passed around Hokkaido, northern Japan. In this study, we investigated the contribution of historical climate change to the heavy snowfall event using large ensemble simulation data sets and two pseudo global warming (PGW) methods. We classified the large ensemble simulation data sets by the pressure pattern and identified the extratropical cyclone event. Composite analyses reveal that the development of the extratropical cyclone can be attributed to historical climate change. We ran the PGW method with the classified meteorological data as the input data and found that the development of the extratropical cyclone resulted in enhanced water vapor transport and intensified local convergence in the lower troposphere, causing heavy precipitation. We also found that oceanic warming made a minimal contribution to the precipitation in this event. These findings highlight the importance of considering historical changes in event-specific synoptic-scale atmospheric conditions when evaluating the contributions of climate change to extreme events.