Supplement to the Characteristics of Precipitation at Haha-jima, Ogasawara (Bonin) Islands

Some outstanding issues noted by Matsuyama (2023) are clarified regarding: (1) digitization Ogasawara (Bonin) Islands before 1978; and, (2) accuracy of 10-day accumulated precipitation data reported by Maejima and Oka (1980). The key findings are as follows: (1) Precipitation data at the Oki-mura Water Supply Branch were digitized from rain gauge charts dating from September 21, 1973 to December 31, 1977. These records were then aligned with daily precipitation data from 1978 to 2022. (2) Of the 153 10-day accumulated precipitation data tabulated 1978, 128 were regarded as probable estimates. Comparing data produced in (1), we found that the discrepancy is within +/- 0.5 mm for 113 data. Hence, we concluded that data regarded to be probable estimates may be used for analyzing monthly and/or long-term variations, although the reason for probable estimates remains unclear. Matsuyama (2023) reported a statistically significant decreasing trend at the 5% level in February's monthly precipitation at Haha-jima from 1978 to 2020. However, this trend is not observed from 1973 to 2022. From 1973 to 2022, monthly precipitation in September and October at both Haha-jima and Chichi-jima shows a statistically significant increasing trend at the 5% level.