Long-Term Changes of Seasonal Progress in Baiu Rainfall Using 109 Years (1901-2009) Daily Station Data

Abstract

This study investigates long-term changes in Baiu rainfall in Eastern and Western Japan using daily precipitation records at 37 stations for the years 1901 through 2009, focusing on its seasonal progress. This period is much longer than various data analyzed in previous observational studies. In the early Baiu season (early to mid June), significant long-term decreasing trends are observed in Eastern and Western Japan, accompanying large inter-decadal variation in the former half of the 20th century. In the late Baiu season (mid to late July), in contrast, significant long-term increasing trends are observed on the Japan Sea side of Eastern and Western Japan. No significant trends are recognized either in the mid Baiu season (late June to early July) or in the entire Baiu season (June to July) over all regions. It is interesting to note that the observed tendency of delayed Baiu withdrawal in the last 109 years, when global warming has been in progress, is similar to its future changes projected by climate models.

Delay of the Baiu Withdrawal in Japan under Global Warming Condition with Relevance to Warming Patterns of SST

“…This change is also interpreted as the delay of the northward movement of the Baiu rainband. Interestingly, the delay of the Baiu withdrawal over Japan in the 20 th century has also been reported from analyses of past observational datasets (e.g., Sato and Takahashi 2001;Inoue and Matsumoto 2003;Endo 2011). Though some related phenomena with respect to the delay of the Baiu withdrawal has been proposed, it is not fully understood, and further examinations are expected.…”

Isotopic Variations Associated with North-South Displacement of the Baiu Front

“…Historical daily precipitation records in Japan (1901−2009) show a significant increasing trend in the amount of precipitation in the late Baiu season (mid-to late-July) over northern Japan (Endo 2011). The physical processes responsible for this trend have been identified in analyses of meteorological patterns over the latter half of the 20th century.…”

Start and End Dates of Rainy Season and their Temporal Change in Recent Decades over East Asia

“…The rainy season firstly withdraws in most parts of North China and Northeast China in August. The withdrawal of the rainy season in eastern China happens from north to south rather than from south to north as reported by Wang and LinHo (2002), and the end dates of the rainy season are much later than those of Baiu over western and central Japan (Sato and Takahashi 2001;Endo 2011). This is because most of the previous studies chose August as the end of the rainy season, but the autumn rain can still meet the standard of the rainy season defined in this paper, which lasts until September in the Yangtze-Huai River basin and the Korean Peninsula, and October in West China and most part of Japan.…”

“…At the same time, Korean summer monsoon rainfall peak has delayed (Lee et al 2010), but the second peak advanced (Ho et al 2003). The early rainy season precipitation significantly decreased in Eastern and Western Japan for period 1901(Endo 2011) and the onset of Baiu front delayed from 1959-1969to 1986-1995(Sato and Takahashi 2001 while the withdrawal of Baiu also delayed for period 1980(Inoue and Matsumoto 2003. However, a systematic analysis of the long-term variation of the rainy season for the whole region has been lacked.…”