Long-Term Changes in Precipitation in Japan

Abstract

This paper explores features of long-term changes in precipitation in Japan based on recent studies using daily data from 51 stations since 1901, partly updated for the present article. We show that heavy daily precipitation (≧ 200 mm and ≧ 100 mm) has significantly increased during the last century as weak to moderate precipitation (≧ 1 mm to ≧ 10 mm) has decreased. New analysis using hourly precipitation records at over 600 stations on the AMeDAS network has shown an increase in very intense hourly and six-hourly precipitations (≧100 mm/h and ≧300 mm/6h) during the last 28 years. It also shows that the trend in the spatial concentration of precipitation during the last century has been increasing, as have changes in the pattern of diurnal variation of precipitation, characterized by a relative increase in precipitation amounts in early morning and a decrease in early afternoon.