Whilst food is cheap, primary industry can meet the needs of the population and combined with the specializations that come with globalization there is no demand to be smarter yet.

Like anything, once a problem is created, a solution will be found.

Why not grow hydroponicically (as you can most) in massive highrise strucutures, saving evaporation, sustaining water and saving land?

The fact is, there is not enough money being spent trying to innovate by private enterprise as the need is not there yet. Sure some govt entities and a small section of business in the world are doing some things, but i would not worry at all as there are many simple solutions, even today.

Water is a problem, but desalination efficiencies will improve, combined with global warming and we will have enough water in the productive places for everything and everyone. Its just the margins who will have to be looked after.

A very good article, David. One point that is not widely understood is the fact that green water can be increased by increasing the velocity of circulation through rain, evaporation/transpiration and back to rain.

For example, the water in the Great Artesian Basin is in a cycle of longer than 100,000 years between infiltration in the Great Dividing Range and bubbling out of a pothole in South Australia. But water from a bore can irrigate a crop and return that water to a faster cycle on the surface. And this is rather ironic in the way many people regard any use of the GAB water as a loss of a resource. But it is a resource that makes no contribution to green water stocks.

At the moment, much of our inland water is locked in a 7 to 15 year cycle and it must be noted that any flow of fresh water into the sea is a loss of green water potential and a reduction in green water cycling frequency.

So evaporation loss from a Dam is still more contributive than fresh water flowing into the sea. An even greater loss of green water is urban storm water, 90% of which once constituted green water in an annual cycle but which now is almost entirely lost into sea water.

Another element would be what could be called "brown water", the water that is 'used' by humans but which remains useful as a green water source. This can be re-used for irrigation and its utility is directly related to the level of nutrients (fertiliser) that humans have added to it. Primary treated sewerage has $9 worth of nitrogen per megalitre and will save a farmer another $9/ML in fertiliser spreading costs. Any disolved soaps (alkalis) will also have a value for reducing the need for lime on acidic soils. Basically the more nutrients left in the water the more valuable the water is to a farmer and the further it can be pumped to a farm user.
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The need for river environmental flows is not incompatible with farming use and they need not be a loss of green water potential. An intensive irrigation requirement based at a river mouth or tidal point, can allow the entire irrigation allocation to be delivered by the river itself and perform most of the environmental flow role at the same time.

Furthermore, environmental flows are the flows that are most suitable and most economic for recycling because they undergo no transformation in their use. If every megalitre has a value then any environmental flow megalitre can be pumped back up the river for re-release. The distance the water can be pumped back is determined by the price of the water and the cost of pumping. And so long as the pumping cost is lower than the wholesale market price of the water then the recycling of environmental flows is profitable and will pay for itself.

In this way, the existing stock of blue water that flows to the sea can be boosted by shifting a portion of it into a much faster cycle. Indeed, the 160km of Brisbane River environmental flows below the Dams can be economically recycled on a 24 hour cycle instead of an annual one. So an annual environmental flow of 170,000 megalitres (equal to Brisbane City's annual use) could, theoretically, be delivered by only 465 megalitres that are recycled each day. The actual volume would need to be increased to cover leakages like evaporation etc. But the remaining 169,500 megalitres could then be left in the Dams to contribute to green water stocks like irrigation or urban use and conversion to brown water and back to green water.

One thing we can conclude from this is that water capture and storage, and irrigation, are not adverse impacts on climate. Far from it, they increase stocks of green water by improving the frequency of green water cycles.

David, a good overview of water use in agriculture.

The retention of rain where it falls has certainly increased with no till farming and improved pasture management and trend still has a way to go.
This, of course, results in less runoff to the river systems. In your terms, blue water is being converted to green water.

Do you know if this factor has been considered when calculating environmental river flows? As farmers retain more of their rainfall I can see an increasing call on the blue dam water for environmental river flows to compensate for the less runoff.

The net effect will be a shift from irrigated to dry land agricultural production. Will this increase or decrease water productivity?

Perseus, your views on environmental flows are attractive.
However, if you nab all the water at tidal reach for irrigation or recycling I am sure there will be a brackish water ecosystem to consider.
Your idea of pumping back upstream may fall over when you consider that the environmental flow may not be 465Megalitres each and every day. Seasonal flushes and periods of low flow would be necessary to mimic the natural flow.

Goeff-and-Perseus),
Thanks for comments. I wrote to generate discussion by people with special insights and to spread concepts that may not be familiar to others. I don't think I can fully answer your question G at the moment though, lets see what other contributers say. Perhaps we need a colour for deep discharges (ochre?!).

As Perseus says, croppers do several environmental services they should be credited for, recycle rain to the atmosphere (not wasted totally) and capture deep (brown?) discharges for green flow. These should be credits against environmental flows. I suspect a coherant and equitable green water credit to Australian farmers has yet to be developed, but would be interested to see other comments on this as it is not something I have yet researched thoroughly.

John Passioura is very good on this:
http://gmopundit.blogspot.com/2006/02/solutions-to-salinity-in-australia.html

"Recently developed options by the Mallee Sustainable Farming Group, of the tactical use of intensive cropping, offer the promise of substantially reducing excessive drainage ( O’Connell MG, O’Leary GJ, Connor DJ (2003) Drainage and change in soil water storage below the root-zone under long fallow and continuous cropping sequences in the Victorian Mallee. Australian Journal of Agricultural Research 54, 663–675; Sadras VO, Roget DK (2004) Production and environmental aspects of cropping intensification in a semiarid environment of southeastern Australia. Agronomy Journal 96, 236–246.). It is the traditional long fallow that has been responsible for much of the deep drainage in that region, and replacing it with crops that keep using water into late spring and early summer reduce that drainage considerably. Moreover, the occasional use of lucerne creates a buffer zone that can accumulate several years worth of drainage before the need to empty it ( Dunin FX, Smith CJ, Zegelin SJ, Leuning R, Denmead OT, Poss R (2001) Water balance changes in a crop sequence with lucerne. Australian Journal of Agricultural Research 52, 247–261.; Zhang L, Dawes WR, Hatton TJ, Hume IH, O’Connell MG, Mitchell DC, Milthorpe PL, Yee M (1999) Estimating episodic recharge under different crop/pasture rotations in the mallee region. Part 2. Recharge control by agronomic practices. Agricultural Water Management 42, 237–249.)"