Agriculture consumes 70 percent of the water used by humans, so finding more efficient ways to water crops seems like a no-brainer to tackle much of the world's increasing shortage of fresh water. Unfortunately, a new study has found that techniques for increased efficiency are actually reducing water availability.
Feeding the Earth’s current population, let alone in a few decades time, can't be done without irrigation. Approximately 40 percent of the calories we consume come from irrigated crops, and that's only going to rise. However, when more efficient irrigation systems are introduced, allowing more crops to be grown for the same amount of water, farmers' responses can subvert the benefits.
“Governments are pouring billions of dollars into making irrigation more efficient, with disastrous consequences for freshwater availability,” said Professor Quentin Grafton of the Australian National University in a statement.
Instead of producing the same amount of food with less water, irrigators may switch to thirstier but more valuable crops or even irrigate fields that were previously not worth tending. Farmers' incomes rise, at least in the short term, but less water is available for downstream users or to preserve ecosystems.
The paradox is one economists have long warned about when resources become cheaper, calling it the Jevons effect. It's not universal, of course. Where crop switching or farmland expansion aren't possible, increased efficiency may indeed reduce water consumption.
Unfortunately, Grafton reports in Science, on a global scale this isn’t usually the case. Besides the shift in economics, Grafton points to a serious problem in our definition of inefficient water use.
When water is “wasted”, a lot of it runs off the field and returns to groundwater or the river from which it was drawn. Increased efficiency can mean reduced inflows to these.
By modeling the three major irrigation types – drip, sprinkler, and surface – and inflows from rainfall and transfers between water basins, Grafton showed the likely damage to water bodies from extra efficiency. The conclusions were confirmed through multiple studies of efficiency programs in river basins across the world.
The paper outlines five steps to address the problem: basin-wide accounting, caps on water taken, pre-efficiency program risk assessments, cost-benefit analyses of efficiency subsidies that include environmental effects, and consideration of how farmers will respond to an effective reduction in water cost.
“This is one of the greatest policy dilemmas of the world,” Grafton said, “how to reconcile increasing freshwater demands with finite freshwater resources.” It's one most governments are pretending doesn't even exist.