小笠原諸島父島は21世紀も乾燥化しているのか

─2000年前後の気候の違いに着目して─

抄録

 Since 1907, Chichi-jima, Ogasawara (Bonin) Islands, has been experiencing a drying trend because of an increase in annual mean temperature and a decrease in annual precipitation, which are particularly pronounced during the summer. However, based on precipitation data prior to 1906, annual precipitation may not have decreased consistently but rather may have fluctuated periodically. Data from the Chichi-jima Meteorological Observatory for the period 1969-2022 are used to clarify trends in annual mean temperature and precipitation, as well as the current drying trend status. The annual mean temperature on Chichi-jima has risen since 1907. The annual precipitation has been cyclical, increasing from 1976 to 2014, indicating that the drying trend on Chichi-jima may be diminishing, including in the summer. Increased precipitation in March, September, and October has contributed to the overall increase in annual precipitation. Typhoons are identified that passed within a 500 km radius of the Chichi-jima Meteorological Observatory as having brought precipitation to Chichi-jima. We found that increased precipitation in October was caused by typhoons. The characteristics of October typhoons that are identified, such as a poleward shift of the maximum tropical cyclone intensity and reduced typhoon velocity, are in accordance with those identified in previous studies that examined future changes in typhoons under global warming.