Considering how blue this planet looks from outer space, it seems strange to worry that water supplies would run dry. But that's exactly what's happening in a lot of major metropolitan areas around the world. Turns out more than half of all global cities with populations greater than 100,000 people are located in regions with depleted water basins.
So what can thirsty cities do to secure a watery future? Well the first step may be getting in touch with local farmers. A new study [PDF] led by Brian Richter of the Nature Conservancy suggests that the key to replenishing city water supplies is forming urban-rural partnerships designed to decrease regional consumption:
A major conclusion is that considerable untapped potential exists for cities to form partnerships with agricultural water users to reduce water consumption on farms, thereby freeing up additional water supply for urban use while potentially reducing the water-related costs of farming, as well as farming’s vulnerability to water shortages.
Agricultural irrigation accounts for the vast majority of water consumption — in the area of 90 percent, according to Richter and company. At the same time, city residents certainly contribute to the situation, since they're the ones consuming most (perhaps two-thirds) of the food produced in the countryside. A shared problem deserves a shared solution, write the researchers.
"This is a reality that governments and cities must come to grips with immediately," they write.
Previous attempts to mitigate the problem have fallen short. Richter and team evaluated the histories of several water-starved cities, such as Phoenix, and found similar patterns of depletion. First local supplies are exhausted, then water is imported from other basins, then recycling and desalination programs are employed.
Over the long-term this unsustainable cycle has dangerous ecological and economic impacts. Taking water from other basins only spreads the problem, and implementing recycling or desalination programs is incredibly expensive. The more we rely on such efforts, the higher our water bills. A far more cost-effective solution, argue the researchers, would be to conserve whatever local supply still exists.
That's where urban-rural partnerships come in. There are a number of ways farmers can reduce the amount of water they use for agriculture; writing at National Geographic, Richter mentions changing crop types or eliminating "low-value" farming, to name just a couple. But the cost of these efforts is so great, and the payoff so far away, that farmers are unlikely to implement them on their own. If cities provided farmers with funding (or incentives or compensation) to change their ways, both sides could ultimately enhance their water supplies.
So while the responsibility goes both ways, according to Richter and company, so does the reward. With an effective water partnership, farmers would spend less on irrigation, and cities, in turn, would save money on the cost of farm goods. Meanwhile, of course, both sides preserve water supplies for the future. The researchers estimate that even a 15 to 20 percent decrease in agricultural water consumption could free up as much water as cities and industries use today.
That's not to say there aren't significant hurdles to such partnerships. For starters, some farmers might be hesitant to work with cities on the problem, for fear of losing control of their supplies. Some policymakers believe that the onus of conservation investment is on the farmers, not the cities, since agriculture is so heavily subsidized. Last, starting new partnerships might punish forward-thinking farmers who already employ conservation techniques.
But Richter and company point out that some cities have already had urban-rural success. Take a water transfer agreement reached by San Diego and its regional irrigation district back in 1998 — the largest rural-urban transfer in U.S. history. Under the terms of the deal, San Diego compensated regional farmers for agricultural water conservation, with the free water being transferred to a canal running into the city. By 2020 the arrangement will provide nearly 40 percent of San Diego's water supply:
"While formidable challenges exist, we believe that the benefits of urban–rural partnerships will be well worth the effort," the researchers conclude.
Images and figures via B. D. Richter, et al. (2013). Tapped out: how can cities secure their water future? Water Policy, 15(3), 335-363. doi:10.2166/wp.2013.105