Long-term changes in the diurnal precipitation cycles in Japan for 106 years (1898-2003)

Changes in the diurnal variation patterns of precipitation were analyzed using four-hourly data for 106 years (1898-2003) at 46 stations in Japan. On the annual and areal average, precipitation amount has a relative increasing trend in the early morning (02-06 JST) and a decreasing trend in the afternoon (14-18 JST), each with a rate of about 5% per century. These changes reflect those of intense precipitation (greater than or similar to 10 mm/4h) in spring and summer, while precipitation amount in autumn and winter shows different changes of diurnal variation patterns. Changes of diurnal cycles of weak precipitation (< 3 mm/4h) are generally small, with a slight relative increase in 06-14 JST, and a decrease in 14-18 JST.