The amount of winter precipitation in Japan is increasing only in the Kanto-Koshin region, which includes the Tokyo metropolitan area located on the Pacific Ocean side of Japan. This study investigated long-term historical changes in winter precipitation in Japan using a large ensemble of regional climate simulations that capture the observed increases in precipitation in the Kanto-Koshin region. In addition, self-organizing maps (SOMs) were applied to the atmospheric pressure to explore historical changes in weather pattern (WP) leading to precipitation. The results suggest that long-term changes in precipitation/snowfall could be due to differences in the WP frequency of southern-coastal cyclones and WP-related precipitation due to altered background states during the winter. The former and latter can be interpreted as dynamic and thermodynamic impacts of historical climate change. As for the Kanto-Koshin region, atmospheric circulation analogs revealed that thermodynamic and dynamic effects account for ~ 2/3 and ~ 1/3 of the precipitation changes, respectively, while dynamic effects (increases in south coast cyclone occurrence) dominantly account for snowfall changes. These changes could be attributed to the large-scale historical increases in air temperature and water vapor content.

日本冬季降水量仅在关东甲信地区增加，其中包括位于日本太平洋一侧的东京都市区。这项研究使用大量区域气候模拟来调查日本冬季降水的长期历史变化，这些模拟捕获了关东甲信地区观测到的降水增加。此外，将自组织图（SOM）应用于大气压力，以探索导致降水的天气模式（WP）的历史变化。结果表明，降水/降雪的长期变化可能是由于冬季背景状态改变导致南部沿海气旋的湿气频率和与湿气相关的降水的差异造成的。前者和后者可以解释为历史气候变化的动态和热力学影响。对于关东甲信地区，大气环流模拟表明，热力学和动力效应分别占降水变化的约 2/3 和约 1/3，而动力效应（南海岸气旋发生的增加）主要是降雪的原因变化。这些变化可归因于历史上气温和水蒸气含量的大规模增加。