Downscaling of Snow Cover Changes in the Late 20th Century Using a Past Climate Simulation Method over Central Japan

We focus on the dramatic decrease in the snow cover on the Japan Sea side of Central Japan in the late 20th century. Using a regional climate model, a control experiment (CTL) was conducted, and it accurately simulated the dramatic decrease in maximum snow depth (SNDmax) between the 1980s and the 1990s. We then conducted a pseudo climate simulation (PCS) in the 1990s, which assumes the mean atmospheric fields in the 1990s and the perturbation from the mean atmospheric fields in the 1980s. The PCS method is expected to evaluate only the impacts of changes in the mean atmospheric fields on the snow cover changes. The PCS simulates the decreases in SNDmax over the coastal area, which are comparable to the changes simulated by the CTL. On the other hand, changes in SNDmax are negligible in the PCS over the mountainous area, where the slight increases in SNDmax are simulated by the CTL. Therefore, the changes in the mean atmospheric fields, especially, the mean temperature rise, are main factors of the snow cover decrease over the coastal area, while changes in both the mean atmospheric fields and the perturbation contribute to the snow cover changes over the mountainous area.