Journal Club

Highlighting recently published papers selected by Academy members

Water, water everywhere, but not enough to farm

Based on human population growth over the last two millennia, Heinz von Foerster and colleagues famously predicted that our population would approach infinity on Friday, 13 November, 2026. Of course, the 1960 doomsday calculation required paradisiacal conditions, including an unlimited supply of food and water. Today, there are already several regions around the world where demand for food and water exceed local supply. But human populations continue to grow in these regions because of the global market for food: exporting food also virtually transfers the water needed to grow that food—called “virtual water”—from production areas to consumption areas. The problem, then, is what happens when the water-rich countries have to limit their virtual-water exports in order to meet the demands of their own growing populations. As Suweis et. al. have calculated in a new Early Edition PNAS paper, the resulting decline of trade-dependent populations could happen as early as 2030, just a few years after von Foerster’s doomsday.

Populations over time. A water-rich country, the U.S. demographic data (red dots) follows the model simulations of carrying capacity based on local water availability (green lines).  In contrast, the UK is a water-poor country, and the demographic data follows the model's prediction of growth driven by virtual carrying capacity (blue lines) enabled by trade.

Populations over time. A water-rich country, the U.S. demographic data (red dots) follows the model simulations of carrying capacity based on local water availability (green lines). In contrast, the UK is a water-poor country, and the demographic data follows the model’s prediction of growth driven by virtual carrying capacity (blue lines) enabled by trade.

To make their calculation, Suweis and his team needed to calculate each nation’s maximum sustainable population, or “carrying capacity,” which they based on currently available water resources for agriculture and livestock. They then incorporated virtual-water imports and exports to calculate each nation’s virtual carrying capacity. As the team readily admits, carrying capacity is difficult to quantify. But the robustness of the resulting model, which is not based on demographic data, suggests that demographic growth was driven by either local or virtual water availability over a forty-year period, 1970-2010, in 52 nations for which the team had data.

Cooperation, new technology, and changes in consumption patterns would help sustain the current food trade system, and the team calculates that cooperation alone could push back the starting date for the decline in trade-dependent populations to 2060, at the latest. However, a recent, intensifying trend suggests long-term global cooperation is unlikely: wealthy nations and some corporations are buying up land and the accompanying water resources of poorer nations, a practice known as land- and water-grabbing. As Rulli et. al. assess for the first time in another Early Edition PNAS paper, there’s been a dramatic increase in these transnational land deals between 2005 and 2009, which the team attributes to rising food demand, dietary changes, and the enhancement of biofuel production.

Water-controlled wealth of nations. Samir Suweis, Andrea Rinaldo, Amos Maritan, and Paulo D’Odorico. PNAS. Published online before print January 28, 2013, doi:10.1073/pnas.1222452110

Global land and water grabbing. Maria Cristina Rulli, Antonio Saviori, and Paolo D’Odorico. PNAS. Published online before print, January 2, 2013. doi: 10.1073/pnas.1213163110 

Categories: Sustainability Science and tagged | | | | | | | | | | | | | | |
Print Email Comment

Leave a Comment

Your email address will not be published. Required fields are marked *