Comments on: Virtual thirst http://www.globaldashboard.org/2008/08/20/virtual-thirst/ Global risks and how to respond to them, edited by Alex Evans and David Steven Sat, 11 Feb 2012 13:49:12 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Alex Evans http://www.globaldashboard.org/2008/08/20/virtual-thirst/comment-page-1/#comment-2038 Alex Evans Wed, 20 Aug 2008 12:41:40 +0000 http://www.globaldashboard.org/?p=1715#comment-2038 And of course, there's also the point that some forms of irrigation are much more water-intensive than others. Furrow irrigation in ditches is very inefficient: up to 75% of the water can be lost. Sprinkler irrigation is a lot better, and drip irrigation's the gold standard: places like Israel, Japan and Taiwan have got their irrigation efficiency up to 50 or 60%. And of course, there’s also the point that some forms of irrigation are much more water-intensive than others. Furrow irrigation in ditches is very inefficient: up to 75% of the water can be lost. Sprinkler irrigation is a lot better, and drip irrigation’s the gold standard: places like Israel, Japan and Taiwan have got their irrigation efficiency up to 50 or 60%.

]]> By: Alex Evans http://www.globaldashboard.org/2008/08/20/virtual-thirst/comment-page-1/#comment-2037 Alex Evans Wed, 20 Aug 2008 12:38:02 +0000 http://www.globaldashboard.org/?p=1715#comment-2037 These figures are global averages as far as I know, so will include both rain-fed and irrigated agriculture. For beef, both of your instances would be included, as well as (much more importantly) the grain used for cattle raised in feedlots rather than open pasture. As your comment accurately implies, there's massive variance within food categories as well as between them. Another dimension of complexity is the question of where crops are grown: very thirsty crops may be fine in an area where there's plenty of water, but very problematic in a water-scarce area. These figures are global averages as far as I know, so will include both rain-fed and irrigated agriculture. For beef, both of your instances would be included, as well as (much more importantly) the grain used for cattle raised in feedlots rather than open pasture.

As your comment accurately implies, there’s massive variance within food categories as well as between them. Another dimension of complexity is the question of where crops are grown: very thirsty crops may be fine in an area where there’s plenty of water, but very problematic in a water-scarce area.

]]> By: David Steven http://www.globaldashboard.org/2008/08/20/virtual-thirst/comment-page-1/#comment-2036 David Steven Wed, 20 Aug 2008 12:31:44 +0000 http://www.globaldashboard.org/?p=1715#comment-2036 If I eat a kg of potatoes, is that 500 litres of water that has fallen from the sky, or 500 litres of additional irrigation? And for beef, is that water that's been piped into a trough, or water that's been absorbed through grass (which itself has been mainly watered by rainfall)? If I eat a kg of potatoes, is that 500 litres of water that has fallen from the sky, or 500 litres of additional irrigation?

And for beef, is that water that’s been piped into a trough, or water that’s been absorbed through grass (which itself has been mainly watered by rainfall)?

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