メモ「消えた"accessible"を追って」

”人類は地球の地表を流れる真水の半分以上を、主に農業に用いている。地表面の水が利用できなくなれば人類は地下水に依存するが、これには化石水が含まれる。化石水は使ってしまうと回復しない。” http://sciencebook.blog110.fc2.com/blog-entry-950.html …
『環境人類学を学ぶ人のために』P・タウンゼンド
[@endBooks]

「人類は地表を流れる真水の半分以上を主に農業に使っている」というのは、世界全体の定量的記述としては正しくない。世界の川の流量は約40兆トン/年、人が使う水は約4兆トン/年、うち灌漑用水は約3兆トン/年である。著者は何か違うことを述べたかったのかもしれないが。 @endBooks
[@masda_ko_1]

のつづき...

原文では"accessible"が入っている。

Humans have taken over more than half of the world's resources for their own use, leading some ecologists to speak of domination of Earth's ecosystems. Humans use more than half of the world's accessible surface fresh water, much of it in agriculture.

[Patricia K. Townsend: "Environmental Anthropology" (2008), p.93]

これの出典は、おそらくVitousek et al (1997)あたり：

Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined; more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet.

[Peter M. Vitousek, Harold A. Mooney, Jane Lubchenco, Jerry M. Melillo: "Human Domination of Earth's Ecosystems", SCIENCE, Volume 277, Number 5325, Issue of 25 Jul 1997, pp. 494-499. (COPY)]

Abstractだと、これだけだが、本文だと"more than half of the runoff water that is fresh and reasonably accessible"という記述：

Water. Water is essential to all life. Its movement by gravity, and through evaporation and condensation, contributes to driving Earth's biogeochemical cycles and to controlling its climate. Very little of the water on Earth is directly usable by humans; most is either saline or frozen. Globally, humanity now uses more than half of the runoff water that is fresh and reasonably accessible, with about 70% of this use in agriculture (20) (Fig. 2).

20: S. L. Postel, G. C. Daily, P. R. Ehrlich, Science 271, 785 (1996)

[Peter M. Vitousek, Harold A. Mooney, Jane Lubchenco, Jerry M. Melillo: "Human Domination of Earth's Ecosystems", SCIENCE, Volume 277, Number 5325, Issue of 25 Jul 1997, pp. 494-499. (COPY)]

この出典であるPostel et al.(1996)は：

[Sandra L. Postel, Gretchen C. Daily, Paul R. Ehrlich: "Human Appropriation of Renewable Fresh Water", Science, New Series, Vol. 271, No. 5250 (Feb. 9, 1996), pp. 785-788]

遠隔地の河川や洪水を除外した分の半分が利用されているという推定。