Future Changes in Tropical and Extratropical Cyclones Affecting Hokkaido and Their Related Precipitation Based on Large-Ensemble Climate Simulations

This study investigates the impact of future climate warming on tropical cyclones (TC) and extratropical cy-clones (ETC) using the database for Policy Decision-Making for Future Climate Change (d4PDF) large ensemble simula-tions. Cyclone tracking was performed using the neighbor enclosed area tracking algorithm (NEAT), and TC and ETCs were identified over the western North Pacific Ocean (WNP). For cyclone frequency, it was revealed that, although a slight underestimation of the total number of TCs and ETCs in both the WNP and near Hokkaido, Japan, exists, the d4PDF re-produced the spatial distribution of both TC and ETC tracks well when compared with observations/reanalysis. The 4-K warming scenarios derived from six different sea surface temperature warming patterns showed robust decreases in TC fre-quency in the tropical WNP and a slight reduction in ETCs near Japan. Next, precipitation characteristics for TCs or ETCs in the vicinity of Hokkaido were examined using 5-km-mesh regional climate ensemble simulations. Four representative cyclone locations near Hokkaido are identified using K-means clustering and revealed distinct precipitation characteristics between clusters, with higher TC-associated precipitation than ETC-associated precipitation and the heaviest precipitation in the southern portion of the prefecture. The 4-K warming scenarios revealed increased precipitation for all cyclone place-ments for both TCs and ETCs. Last, average cyclone intensity, translation speed, and size were examined. It was shown that TCs in future climates are more intense, propagate more slowly, and are smaller in terms of enclosed vorticity area as they approach Hokkaido. For ETCs, mean intensity does not change much; they travel slightly faster, and become smaller.