Study of Recent Variation in Weak Rainfall over Japan Using 31-Year AMeDAS Dataset

Linear regression analysis was applied to the time series of hourly rainfall data between June and September for 31 years to elucidate the features of weak rainfall over Japan. Many stations exhibiting a significant positive trend in the frequency of weak rainfall (1.5 mm h(-1)) were localized in the Hokkaido district. In contrast, there were only a few stations with a significant positive trend in weak rainfall over regions other than Hokkaido; however, many stations exhibited a significant positive trend in heavy rainfall exceeding 25 mm h(-1). Thus, there existed a clear geographical contrast between the two regions.