How Wet Crops Get

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Science  24 Oct 2008:
Vol. 322, Issue 5901, pp. 507
DOI: 10.1126/science.322.5901.507a

One of the major challenges posed by both increasing global population and climate change is the wise use of water. An enormous quantity of fresh water is used in agriculture, and planning in the face of dwindling resources requires an understanding of current and past consumption. With the aid of a global vegetation and water balance model, Rost et al. provide a global assessment of agricultural water use and evaluate how changes in land use affected water consumption during the 20th century. Their analysis shows that although globally agriculture is mostly based on the use of precipitation directly, major agriculture in India, China, Pakistan, and the United States depends heavily on diversions from rivers or groundwater; about half is from nonrenewable sources. Historically, their analysis implies that the global expansion of agriculture since 1900 probably increased discharge by nearly 5% (despite an increase in withdrawals for irrigation over time), an amount about comparable in some cases to effects from climate change alone. Thus, land-use changes need to be considered in adapting water use to climate change. — BH

Water Resour. Res. 44, 10.1029/2007WR006331 (2008).

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