地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
寄書
写真と図で見る「37年ぶりの大渇水」
─小笠原諸島父島,母島における少雨時(2016~2017年)と平常時(2018年)の状況の比較─
松山 洋
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2018 年 127 巻 6 号 p. 823-833

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 A period with less than average precipitation on Chichi-jima and Haha-jima in the Ogasawara (Bonin) Islands between 2016 to 2017 was compared to 2018 (normal year), based on field surveys conducted in March 2017 and February 2018. Water consumption showed a six-day cyclic variation, reflecting the voyage schedule of the marine vessel Ogasawara-maru connecting Chichi-jima and central Tokyo. Water consumption increased on the day Ogasawara-maru arrived at Chichi-jima, because the number of passengers sometimes corresponded to about 30% of number of residents on Chichi-jima. Compared to Chichi-jima, annual precipitation on Haha-jima was about 100 mm greater during the period 2007-2017, along with distinctly greater precipitation in May compared to April and June. In addition, precipitation on Haha-jima in August was the highest among all months. Even during a severe drought in 2016-2017, precipitation in August 2016 was greater than the average from 2007 to 2017 on Haha-jima, recovering water stored by the Chibusa dam which supplies drinking water on Haha-jima. The effective water storage per capita on Haha-jima is 1.5 times more than that on Chichi-jima, which in some part resulted in the temporal change in the percentage of water storage always being larger on Haha-jima. Both on Chichi-jima and Haha-jima, people tried to overcome the difficult situation of the severe drought, reflecting efforts by the local government to communicate the need to save water.

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© 2018 公益社団法人 東京地学協会
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