Decrease in Baiu Precipitation and Heavy Rainfall Days in Late June of the 2000s in Northwestern Kyushu, Western Japan

Abstract

From daily precipitation data for June-July of 1971-2010, we examined the features and year-to-year variations of the Baiu precipitation around the Kyushu District, western Japan. The total precipitation in the Baiu season (June-July) at Nagasaki (located in northwest Kyushu) significantly decreased during the 2000s (2001-2010), mainly during June, at the 95% confidence level. The area with the largest decrease extended widely over northwestern Kyushu, while precipitation in southern Kyushu increased during the 2000s. Such regional precipitation contrasts appeared in late June, during the mature Baiu season. The decrease in total precipitation, as in Nagasaki, in late June during the 2000s was a reflection of the “heavy rainfall days” (with rainfall ≥ 50 mm day^-1). It is suggested that less frequent appearance of Baiu frontal zone with wider meridional extension of the heavy rainfall area resulted in such features during the 2000s, although the Baiu fronts' appearance frequency on the surface weather maps was not very different from that before 2000.