More Irrigation with Less Water: China 2009; Canterbury 2010; DPC 1978, 1985
China’s Water Resources Minister, Chen Lei, announced in February last year that they plan to reduce water use per unit of GDP 60% by 2020. On average, China is short of 40 000 million m3 of water per year [about 30 m3 per person]: 300 million people have insufficient drinking water and 15.3 million hectares [approximately the area of South Island, 13% of China’s farm land] is subject to drought every year. Agriculture, which implies irrigation, accounts for 70% of water use already so clearly there is a dilemma. The Water Resources Ministry intends to move from policy exploiting water resources to a strategy making better use of existing water supplies by water demand management. They will invoke three ‘red lines’: on water extraction; waste water disposal; and efficiency of water use.
Draft ‘outcome targets’ are currently being reviewed for the Canterbury Water Management Strategy. Among nine ‘target areas’, five are: ecosystem health/biodiversity; natural character of braided rivers; drinking water; water use efficiency; irrigated land area. Canterbury has 70% of New Zealand’s irrigated land area, about half a million hectares irrigated out of 1.3 million hectares considered to be ‘irrigable’. Ten of about 30 groundwater allocation zones are estimated by Environment Canterbury to be “red” – over-allocated; four more are “yellow” – over 80% allocated. The Strategy has ‘goals’ for much increased irrigated area [perhaps up to 70% more] by 2040. Also clearly, this is another dilemma – how to do this while recognising goals for ecosystem health/biodiversity and the natural character of braided rivers, in particular. So the target area ‘water use efficiency’ is set to be significant.
Peter Carran and David Painter proposed an appropriate set of definitions of volumetric irrigation efficiency more than 30 years ago [see ‘What is Irrigation Efficiency?’ in Publications, Technical]. The topic was explored further 25 years ago in an article entitled ‘More Irrigation with Less Water’ [q.v. ibid.]. There can be more irrigation, with less water, only if there is more ‘irrigation-with-less-water’. That is happening in Canterbury already, for example when centre-pivot irrigation from on-farm storage replaces border-dyke irrigation from rostered open-channel supply. And there can be more irrigation, with more water, without prejudice to ecosystem and social water values, by making better use of the time-availability of surface water supplies – which implies storage. Storage, whether for irrigation or hydro-electricity, has had bad press in Canterbury in recent years. But how many people would want to do without the storage, and therefore the convenient electricity, that modified and controlled lakes like Pukaki and Tekapo provide? Even while useful debate on conservation and development of water resources in Canterbury continues, most interested parties should be able to agree that not wasting water, but using as little as possible of the appropriate quality to satisfy the intended purpose, will be an important aim.
Sources: http://www.nature.com/news/2009/090219/full/news.2009.111.html; http://www.canterburywater.org.nz/downloads/011%20Canterbury%20Water%20Management%20Strategy%20document%2024%2011%2009..pdf