The noisy debate over fuel-vs-food is rising in volume, but there is less spoken about the water required to irrigate the land on which the crops are to be grown. It is well-recognised that China is the new industrial nation, in an unparalleled phase of its economic and social development. This might be expected to continue for as long as the West can afford to buy its cheap goods, but in the current recession, that duration is debatable. Underpinning Chinese industrial growth, as for all industrial growth, is energy, and in the recognition of peak oil, emphasis is on biofuel (and all other kinds of energy resource in China, including coal-to-liquids) as products need to be transported for sale. It is aimed that by 2020, 12 million metric tons of biofuel will be produced in China. To put this into context, this is around one fifth of the fuel used in the United Kingdom, per annum.
The fuel is to be ethanol, fermented from corn (maize) which is a relatively water-efficient starch crop. According to a recent analysis (1) to irrigate sufficient corn to produce 12 million tonnes of bioethanol a quantity of water equivalent of the annual discharge of the Yellow River would be required. 64% of China's arable (crop-growing) land is in the northern part of the country, and is already under pressure since the existing use of water exceeds its reserves and water-tables are falling (2).
We have neither sufficient land nor water to maintain the illusion that we can continue as we are, certainly not in terms of liquid transportation fuel and thus transport itself, merely by substituting declining oil and natural gas by biofuels.
Massive water demand should be anticipated in consequence of from expanding biofuel production in other countries too. For example, in India and in the western United States, water tables are also falling. In the latter case, the agriculture is maintained by draining "fossil water" - the Ogallala aquifer which underlies 8 U.S. states. It is voiced too that climate change and the shifting of the temperate regions north may impact further on the American West. In Australia too, another major producer of starch crops, water supplies are also under stress.
It has been reckoned (3) that some 5,000 - 6000 cubic kilometers (km^3) of water would be needed to water enough maize to supplant the world's petroleum based fuel by ethanol generated from corn, in comparison with the entire supply of fresh water available on Earth of 13,500 km^3 - i.e about half of it.
Other potential fuel crops, e.g. wheat, soybeans and rapeseed are even thirstier in their demand for water than corn is.
This is a salient warning and another nail in the coffin of crop-based biofuels. For instance if all the U.K.s crop-land were turned over to make biofuels and no food grown we could still match a mere 10% of our annual fuel budget. I hold out hope for hydrothermal methods, processing waste biomass and algae into liquid transportation fuels and gases, but on a far reduced scale of transportation than we are used to.
We have neither sufficient land nor water to maintain the illusion that we can continue as we are, merely substituting declining oil and natural gas by biofuels.
(1) H. Yang, Y. Zhou, J. Liu. Land and water requirements of biofuel and implications for food supply and the environment in China. Energy Policy (in press)
(2) S. Khan, M.A. Hanjra, J. Mu Water management and crop production for food security in China: a review. Agricultural Water Management 2009; 96: 349-360.
(3) L.Reijnders, http://scitizen.com/stories/future-energies/2009/04/Biofuels-and-water/