Crossposted with www.thegreengrok.com.
Is virtual water a virtue?
That's the question asked by Paolo D'Odorico of the University of Virginia and colleagues in a paper published in the journal Geophysical Research Letters.
If bread is the staff of life, water is the ground we walk on. None of us can survive without water. In fact without water, the grain needed to make bread or any other food item would never even get harvested.
By the way food production looms large in this equation -- agriculture is by far the biggest water user, much bigger in most areas than that used for drinking (see sources here and here).
For millennia, water availability played a key role in determining a region's carrying capacity -- how many people could survive there. Regions with an abundance of water had potentially large carrying capacities while water-poor or dry regions were limited in the populations that could be supported. A region's exact carrying capacity was no doubt affected by a host of other factors such as climate, amount of land allocated to agriculture, type of diet, and soil fertility. But without water all bets were off.
That Was Then -- Today We Are Hydro-Empowered, Sort of
The limitations imposed by water availability have declined with the advent of the global economy. Now water-rich regions can produce an excess of food and export it to a water-poor region, effectively (some might say artificially) enhancing the water-poor region's apparent carrying capacity. Since such exported foodstuffs require water, they are considered both food and what scientists refer to as virtual water exports, with the amount of the latter equaling the amount of water required to grow the food.
The upshot is that the transfer of virtual water allows the populations of water-poor regions to grow well beyond their indigenous carrying capacities. As a result, our total global population has increased. From a survival-of-the-species point of view, this might seem great -- if our life's purpose is to propagate, then the more the merrier.
But not everyone agrees with that assessment. Pointing to the unsustainability of such an arrangement, some argue the artificially large populations are decimating ecosystems and contributing to the emissions of heat-trapping greenhouse gases. Moreover, the excess water in many so-called water-rich regions is drawn from non-renewable sources, such as deep aquifers. When these sources are depleted, there will not only be no more virtual water -- there won't be water.
The Toll of Virtual Water
Now, D'Odorico and his colleagues look at a different aspect of this conundrum: the toll in deaths and suffering brought about by the dependence on virtual water. Their study used a simple model to simulate the effect of the export/import of virtual water on both water-rich and water-poor populations. As expected, they find that as the amount of transfer of virtual water increases, the population of water-poor regions increases while the population of the water-rich regions remains the same. Hence total global population increases.
But what happens if there are droughts? To answer, the authors redid their model simulations but now with random droughts added in. Again not surprisingly, global populations decrease when droughts are included, but they are still larger than without virtual water transfer and they increase as the amount of virtual water transfer increases.
But here's the kicker: The simulated number of people who die from droughts increases with increasing amounts of virtual water transfer. Because populations in water-poor regions grow with more virtual water transfer, they become vulnerable to -- and so more people die from -- drought.
So, the D'Odorico paper poses a difficult but intriguing question. Are we better off as a people:
- using export/import of virtual water to maximize global populations at the expense of periodic episodes of high mortality from droughts, or
The Authors' Proposed Solution
Going out on a limb, the authors propose a hybrid between no virtual water transfers and unfettered transfer. In their world, which they dub "water solidarity," transfers would not be routine, but would only occur on an emergency basis whenever droughts threaten survival in a given region. Their model simulations demonstrate that such an arrangement would yield global populations only slightly larger than those without any virtual water transfer but with far fewer drought-induced deaths.
Interesting idea, but, as the authors themselves concede, their model-simulated, water-solidarity world is highly idealized -- one in which global aid organizations can mobilize rapidly to respond to a water crisis and one with adequate infrastructure to get the virtual water (i.e., food) to the affected populations on time. Past experience suggests we still have a way to go on that one.
Some Cultural Issues to Consider
I could be way off base, but I suspect that the survival of most of us in the Geophysical Research Letters/TheGreenGrok world are not threatened by having too little real or virtual water. Isn't it possible that many in water-poor regions of the developing world would view this issue differently than we?
Even in the water-solidarity world, the water-poor populations would, over the long term, be limited by the availability of virtual water (i.e., food). Isn't it likely that life in regions whose populations are constrained by the availability of food is shall we say sub-optimal? Would you opt for such a life or would you prefer to get the virtual water and deal with the eventuality of drought when it happened?
At the very least the desire for more food would make the water-solidarity world a difficult one to maintain in an operational sense. If it could be maintained, it might still lead to massive immigration from water-poor to water-rich regions, creating similar strains on resources.
There are no easy answers here, but great fun to debate. Also essential to think about. The issues raised by D'Odorico and his colleagues are at the core of envisioning how we get from where we are today to a long-term, sustainable path.
If I were fond of puns, I would say that the issue raised by D'Odorico et al is "virtual water for thought." Oops.