Changes of precipitation amounts and extremes over Japan between 1901 and 2012 and their connection to climate indices

Annual and seasonal precipitation amounts and annual precipitation extreme indices for Japan were characterized for the period 1901–2012 using the Mann–Kendall Tau test, regional analysis, and probability distribution functions, and possible correlations with climate indices including the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation, the Southern Oscillation Index (SOI), and the sea surface temperature were explored using wavelet analysis. The results indicate that precipitation amounts exhibited a substantial decrease at both the annual and seasonal scales, and the fluctuation became more frequent and stronger in the recent decades. Precipitation tended to be concentrated in summer and autumn throughout Japan and the southwest had higher precipitation than the southeast in the spring, summer, and autumn, with precipitation concentrated in the southeast in the winter. On a regional scale, the number of heavy precipitation days, consecutive wet days and total wet-day precipitation indicated a decreasing trend, while an increasing trend for maximum 1- and 5-day precipitation amount, precipitation in very wet days and the number of consecutive dry days. These changes have been an important issue for supplying the demand of water resources in Japan. Continuous wavelet analysis shows that there were significant periodic variations at 2–3 and 5–13 years frequency in extreme precipitation. In addition, climate indices have significant correlations with extreme precipitation, for example, there is statistically significant association between the increasing extreme precipitation and SOI.