Long-term Changes in Japanese Extreme Precipitation Analyzed with APHRO_JP_EX

抄録

The authors constructed a dataset of historical extreme precipitation indices in Japan named APHRO_JP_EX. This dataset contains more than 40 annual indices derived from daily precipitation. Although the spatial coverage is limited to the land of Japan, the uniqueness of these data with their long period (1900-2009) and high resolution (0.05 x 0.05 degrees) is useful not only for climate research but also for application to studies such as risk assessment of hydrological disasters. Using this dataset, we analyzed trends and annual variations of these indices to quantify the effects of global warming on local extreme precipitation in Japan.

The number of wet days has significantly decreased all over Japan, especially in the northeastern part, where about 20 wet days per year have been lost during the past century. The annual mean precipitation has slightly decreased in most regions. Looking at the regional average of all of Japan, increased heavy precipitation intensity is distinct. The local changes in heavy precipitation are larger in the western part; however, they are not significant in many areas due to large annual variations. When the former and the latter halves of the 20th century are compared, increases in the annual variations of heavy precipitation indices are remarkable in the latter period. While indices of wet spells and dry spells show clear regionality in their trends, wet-spell indices have been decreasing on the Japan Sea side and dry-spell indices have been increasing on the Pacific Ocean side, though both results indicate a progression of meteorological dryness.

After the beginning of the 20th century, in which surface temperatures were rising, precipitation in Japan has become more extreme overall; however, we found regional differences in these signals.