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MIT 12 000 - Study Notes

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Article Contentsp. 785p. 786p. 787p. 788Issue Table of ContentsScience, New Series, Vol. 271, No. 5250 (Feb. 9, 1996), pp. 729-876Front Matter [pp. 729-773]Editorial: An Enhanced Perspective [p. 741]LettersHormonal Activity [p. 743]Biological Determinism [pp. 743-744]Low-Angle Faults [pp. 744-745]The Science Doctorate [pp. 745-747]Gene Therapy: False Expectations? [p. 747]ScienceScope [p. 749]NewsARC Affair Troubles French Scientists [pp. 750-751]NIH Clinical Center Gets a Boost [pp. 751-752]Showdown at the UC Corral [p. 752]Two Eyes are Better Than One [p. 752]Russian Deal Bolsters the Space Station-at a Price [pp. 753-754]A Familiar Face for a Distant Galaxy? [p. 754]Results on New AIDS Drugs Bring Cautious Optimism [pp. 755-756]Galactic Building Blocks Found? [p. 756]Where Do Meteorites Come From? A NEAR Miss May Tell [p. 757]Collisions Hint That Quarks Might Not Be Indivisible [p. 758]Do Galaxies Fly Through the Universe in Formation? [p. 759]Moving Forest Trees Into the Modern Genetics Era [pp. 760-761]Random Samples [p. 763]Special News ReportScience Journals Go Wired [pp. 764-766]Electronic Preprints Point the Way to 'Author Empowerment' [pp. 767-768]Book ReviewsReview: Advances for Epidemiology [p. 770]Review: A Global Campaign [pp. 770-771]Review: Other Health Issues [p. 771]PerspectivesProbing Catalysts with Water [pp. 774-775]An Ice Shelf Breakup [pp. 775-776]Indeterminate Organization of the Visual System [pp. 776-777]On Hierarchies: Response to Hilgetag et al [p. 777]Intercalation, DNA Kinking, and the Control of Transcription [pp. 778-784]ReportsHuman Appropriation of Renewable Fresh Water [pp. 785-788]Rapid Collapse of Northern Larsen Ice Shelf, Antarctica [pp. 788-792]DNA: An Extensible Molecule [pp. 792-794]Overstretching B-DNA: The Elastic Response of Individual Double-Stranded and Single-Stranded DNA Molecules [pp. 795-799]On the Nature of Water Bound to a Solid Acid Catalyst [pp. 799-802]Mutagenesis in Mammalian Cells Induced by Triple Helix Formation and Transcription-Coupled Repair [pp. 802-805]Cell Killing by the Drosophila Gene reaper [pp. 805-807]Requirement of an ICE-Like Protease for Induction of Apoptosis and Ceramide Generation by REAPER [pp. 808-810]Stimulation of Membrane Ruffling and MAP Kinase Activation by Distinct Effectors of RAS [pp. 810-812]PKC-Dependent Stimulation of Exocytosis by Sulfonylureas in Pancreatic β Cells [pp. 813-815]Cold-Induced Expression of $\Delta^9$-Desaturase in Carp by Transcriptional and Posttranslational Mechanisms [pp. 815-818]Identification of a Committed Precursor for the Mast Cell Lineage [pp. 818-822]Activation of BTK by a Phosphorylation Mechanism Initiated by SRC Family Kinases [pp. 822-825]Back Matter [pp. 826-876]Human Appropriation of Renewable Fresh WaterAuthor(s): Sandra L. Postel, Gretchen C. Daily, Paul R. EhrlichSource: Science, New Series, Vol. 271, No. 5250 (Feb. 9, 1996), pp. 785-788Published by: American Association for the Advancement of ScienceStable URL: http://www.jstor.org/stable/2889886Accessed: 24/09/2008 10:49Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unlessyou have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and youmay use content in the JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained athttp://www.jstor.org/action/showPublisher?publisherCode=aaas.Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with thescholarly community to preserve their work and the materials they rely upon, and to build a common research platform thatpromotes the discovery and use of these resources. For more information about JSTOR, please contact [email protected] Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve andextend access to Science.http://www.jstor.orgThe Amazon River accounts for 15% of global runoff ( 1). It is currently accessible, however, to -25 million people (12) 0.4% of world population and no massive expansion of irrigation is likely that would warrant major diversiolns from it. We thus consider 95% of its flow inaccessible. The Zaire-Congo ranks second in global runoff (3.5% of the total) (11) and supports -1.3% of world population (12). We judge half of its flow to be inaccessible for pur- poses of irrigation and in-duLstrial and mu- nicipal use over the next 30 years. The final subtraction is for the remote rivers of North America and Eurasia, 55 of which have no dams on their main chan- nels (1 3). Most of this river flow is in tundra and taiga biomes that are remote from pop- ulation centers. The combined average an- nual flow of these northern untapped rivers is 1815 km3/year, and we subtract 95% of it. Together, the inaccessible remote flows of the Amazon, Zaire-Congo, and northel-rn- tier uindeveloped rivers amount to 7774 km3 per year (Table 3), or 19% of total annual ruLnoff. This leaves -32,900 km3 geograph- ically accessible. Our estimate is conserva- tive because we made no subtractions for many (particularly northern) rivers that have very large flows relative to the human population size and water needs of their geographic areas (14). We next adjusted for temporal inacces- sibility. Irrigated agriculture, industry, and households require that water be supplied when and where it is needed. This degree of control over runoff is not easy to achieve. Approximately 11,100 km3 of global runoff (-27% of the total) is renewable ground water and base river flow (6). As long as extraction does not exceed replenishment, these souLrces can provide a reliable renew- able supply. The remaining runoff, -29,600 kmi3, is much harder to capture, because most of it is flood water. In Asia, for in- stance, 80% of runoff occurs from May to October (4, 15). Capturing flood runoff generally requires the construction of dams. The present storage capacity of large dams collectively totals 5500 kmi3, of which 3500 km3 is actively used in the


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