PNAS (The Proceedings of the National Academies of Science of The United States of America) has just published an interesting study, undertaken by Samir Suweisa, Andrea Rinaldob, Amos Maritana, and Paolo D’Odoricod. Titled “Water Controlled Wealth of Nations“, the study takes a look at the dependence of national population growth on available water resources, and divides nations into several classes related to their ability (or lack thereof) to export water. The curious thing here is that water is not merely analyzed as water, but includes what they term as “virtual water” — water resources embedded in internationally traded foodstuffs. They foresee a likelihood of population declines in water scarce nations as population growth in water abundant nations force these nations to curtail exports of virtual water (food); they develop formulas which suggest these population declines may begin around 2040.
Population growth is in general constrained by food production, which in turn depends on the access to water resources. At a country level, some populations use more water than they control because of their ability to import food and the virtual water required for its production. Here, we investigate the dependence of demographic growth on available water resources for exporting and importing nations. By quantifying the carrying capacity of nations on the basis of calculations of the virtual water available through the food trade network, we point to the existence of a global water unbalance. We suggest that current export rates will not be maintained and consequently we question the long-term sustainability of the food trade system as a whole. Water-rich regions are likely to soon reduce the amount of virtual water they export, thus leaving import-dependent regions without enough water to sustain their populations. We also investigate the potential impact of possible scenarios that might mitigate these effects through (i) cooperative interactions among nations whereby water-rich countries maintain a tiny fraction of their food production available for export, (ii) changes in consumption patterns, and (iii) a positive feedback between demographic growth and technological innovations. We find that these strategies may indeed reduce the vulnerability of water-controlled societies.