The World in 2050: Four Forces Shaping Civilization's Northern Future

1109-1126; A. T. Wolf, “Shared Waters: Conflict and Cooperation,” Annual Review of Environment and Resources 32 (2007): 241-69.

222 See http://biblio.pacinst.org/conflict/ and http://worldwater.org/conflictchronology.pdf and http://www.transboundarywaters.orst.edu/.

223 J. I. Uitto, A. T. Wolf, “Water Wars? Geographical Perspectives: Introduction,” The Geographical Journal 168, no. 4 (2002): 289-292; T. Jarvis et al., “International Borders, Ground Water Flow, and Hydroschizophrenia,” Ground Water 43, no. 5 (2005): 764-770.

224 W. Barnaby, “Do Nations Go to War over Water?” Nature 458 (2009): 282- 283.

225 Water “withdrawal” refers to the gross amount of water extracted from any source in the natural environment for human purposes. Water “consumption” refers to that part of water withdrawn that is evaporated, transpired, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Global “blue water” withdrawals from rivers, reservoirs, lakes, and aquifers are estimated at 3,830 cubic kilometers, of which 2,664 cubic kilometers are used for agriculture. Pp. 67-69, Water for Food, Water for Life: A Comprehensive Assessment of Water Management in Agriculture (London: Earthscan, and Colombo: International Water Management Institute, 2007), 665 pp.

226 The term virtual water was coined by J. A. Allan in the early 1990s, e.g., “Policy Responses to the Closure of Water Resources,” in Water Policy: Allocation and Management in Practice , P. Howsam, R. Carter, eds. (London: Chapman and Hall, 1996).

227 The global transfer of virtual water embedded within commodities is estimated at 1,625 billion cubic meters per year, about 40% of total human water consumption. A. K. Chapagain, A. Y. Hoekstra, “The Global Component of Freshwater Demand and Supply: An Assessment of Virtual Water Flows between Nations as a Result of Trade in Agricultural and Industrial Products,” Water International 33, no. 1 (2008): 19-32. See also pp. 35 and 98, UN World Water Assessment Programme, The United Nations World Water Development Report 3: Water in a Changing World (Paris: UNESCO, and London: Earthscan, 2009), 318 pp.

228 R. G. Glennon, Water Follies: Groundwater Pumping and the Fate of America’s Fresh Waters (Washington, D.C.: Island Press, 2002), 314 pp. Windmills and other early technology could lift water from a maximum depth of only seventy to eighty feet, but the centrifugal pump, powered by diesel, natural gas, or electricity, could lift water from depths as great as three thousand feet.

229 Figure 7.6, UN World Water Assessment Programme, The United Nations World Water Development Report 3: Water in a Changing World (Paris: UNESCO, and London: Earthscan, 2009), 318 pp.

230 U.S. Geological Survey, “Estimated Use of Water in the United States in 2000,” USGS Circular 1268, February 2005.

231 Other materials can also make good aquifers, for example gravel or highly fractured bedrock.

232 See M. Rodell, I. Velicogna and J. S. Famiglietti, “Satellite-based Estimates of Groundwater Depletion in India,” Nature 460 (2009): 999-1002, DOI:10.1038/nature08238; and V. M. Tiwari, J. Wahr, and S. Swenson, “Dwindling Groundwater Resources in Northern India, from Satellite Gravity Observations,” Geophysical Research Letters 36 (2009), L18401, DOI:10.1029/2009GL039401.

233 Also known as the High Plains Aquifer, the Ogallala underlies parts of Kansas, Nebraska, Texas, Oklahoma, Colorado, New Mexico, Wyoming, and South Dakota. Other material in this section drawn from V. L. McGuire, “Changes in Water Levels and Storage in the High Plains Aquifer, Predevelopment to 2005,” U.S. Geological Society Fact Sheet 2007-3029, May 2007.

234 Human drawdown averages around one foot per year, but natural replenishment is less than an inch per year. Telephone interview with Kevin Mulligan, April 21, 2009.

235 “Useful lifetime” is projected time left until the saturated aquifer thickness falls to just thirty feet. When the aquifer is thinner than thirty feet, conventional wells start sucking air, owing to a thirty-foot cone of depression that forms in the water table around the borehole. The described GIS data and useful lifetime maps for the Ogallala are found at http://www.gis.ttu.edu/OgallalaAquiferMaps/.

236 LEPA drip irrigation systems create a smaller cone of depression, allowing water to be sucked from the last thirty feet of remaining aquifer saturated thickness. Therefore a switch to LEPA can prolong the usable aquifer lifetime another ten to twenty years, but cannot stop the outcome.

237 Notably the Netherlands, France, Germany, and Austria. P. H. Gleick, “Water and Energy,” Annual Review of Energy and the Environment 19 (1994): 267-299. This is not to say all of the water used is irrevocably lost; most power plants return most of the heated water back to the originating river or lake. See note 225 for withdrawal vs. consumption.

238 This is the legal maximum in the European Union, but recommended “guideline” temperatures are lower, around 12-15 degrees Celsius in the EU and Canada. Ibid.

239 See also his book on wind power. M. Pasqualetti, P. Gipe, R. Righter, Wind Power in View: Energy Landscapes in a Crowded World (San Diego: Academic Press, 2002), 248 pp.

240 The reason for this is the very large water losses that evaporate from the open reservoirs behind hydroelectric dams.

241 For example, see P. W. Gerbens-Leenes, A. Y. Hoekstra, T. H. van der Meer, “The Water Footprint of Energy from Biomass: A Quantitative Assessment and Consequences of an Increasing Share of Bio-energy in Energy Supply,” Ecological Economics 68 (2009): 1052-1060.

242 Telephone interview with M. Pasqualetti, April 14, 2009.

243 T. R. Curlee, M. J. Sale, “Water and Energy Security,” Proceedings, Universities Council on Water Resources, 2003.

244 For climate model simulations of Hadley Cell expansion, see J. Lu, G. A. Vecchi, T. Reichler, “Expansion of the Hadley Cell under Global Warming,” Geophysical Research Letters 34 (2007): L06085; for direct observations from satellites, see Q. Fu, C. M. Johanson, J. M. Wallace, T. Reichler, “Enhanced Mid-latitude Tropospheric Warming in Satellite Measurements,” Science 312, no. 5777 (2006): 1179.

245 P. C. D. Milly, K. A. Dunne, A. V. Vecchia, “Global Pattern of Trends in Streamflow and Water Availability in a Changing Climate,” Nature 438 (2005): 347-350.

246 G. M. MacDonald et al., “Southern California and the Perfect Drought: Simultaneous Prolonged Drought in Southern California and the Sacramento and Colorado River Systems,” Quaternary International 188 (2008): 11-23.

247 The medieval warming was triggered by increased solar output combined with low levels of volcanic sulfur dioxide in the stratosphere, whereas today the driver is greenhouse gas forcing. The comparison between the medieval warm period and today is imperfect because the former saw temperatures rise most in summer, whereas greenhouse gas forcing causes maximum warming in winter and spring. Still, the medieval warm period is the best “real world” climate analog scientists have for examining possible biophysical responses to projected greenhouse warming. For more, see G. M. MacDonald et al., “Climate Warming and Twenty-first Century Drought in Southwestern North America,” EOS, Transactions, AGU 89 no. 2 (2008). For more on the Pacific Decadal Oscillation, see G. M. MacDonald and R. A. Case, “Variations in the Pacific Decadal Oscillation over the Past Millennium,” Geophysical Research Letters 32, article no. L08703 (2005), DOI:10.1029/2005GL022478.

248 R. Seager et al., “Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America,” Science 316 (2007): 1181-1184.

249 P. C. D. Milly, J. Betancourt, M. Falkenmark, R. M. Hirsch, Z. W. Kundzewicz, D. P. Lettenmaier, R. J. Stouffer, “Stationarity Is Dead: Whither Water Management?” Science 319 (2008): 573- 574.

250 The confusion arises from the fact that the “hundred-year flood,” “five-hundred-year flood,” etc., are simply statistical probabilities expressed as a flood height. This leads the common misperception that a hundred- year flood happens only once every hundred years, a five-hundred-year flood happens only once every five hundred years, and so on. In fact, the probability is 1/100 and 1/500 in any given year. The likelihood of enjoying a hundred