Growing food to feed the world accounts for 70 percent of fresh water consumption. But the need for irrigated crops is coming into increasing conflict with the fresh water requirements of cities, factories and a healthy environment. U.S. farmers and scientists are trying to tackle the dilemma.
It's been a wet winter in Colorado. For the first time in many years, Dave Petrocco says the soil needs to dry out. "We're about a month late this year," he reports. "It's time to put the crops in that we normally do this time of year, such as the spinaches, lettuce, onions, sweet peas." With almost 1,000 hectares to be planted, the third generation farmer says it's hard to wait. But as he gazes across an empty brown field, he adds that too much water is a rare event. "We're on an irrigated desert, and water has become an extremely precious resource."
To prepare for that unavoidable summer day when the soil will be too dry, Petrocco's been installing more drip irrigation. It's expensive, but it uses 40 percent less water than traditional flood irrigation. That's important because, over the years, his annual water allocations have been cut back and the drip system allows the farmland to produce as much as it did before.
In the U.S., states monitor water use and distribution. Petrocco's water allocation has been trimmed due to growing competition between Colorado's cities and farms. By 2025, it's likely that every state in the nation will face the same crisis. That's according to experts at the American Association for the Advancement of Science annual meeting, held recently in San Francisco.
One way to reduce these conflicts is to develop plants that can tolerate saltier water, or less water. A new variety of drought-tolerant rice should be available soon, but John Bennet, with the International Rice Research Institute in the Philippines, says there will be trade-offs. "Rice roots tolerate submergence, and water can therefore be used to control weeds," he explains. "In monsoonal Asia, there was no shortage of water during the wet season. So it made sense to grow a crop and use water as a natural herbicide." For rice in dryer fields, he says, farmers may have to increase herbicide use or weeding.
Another approach is to make every drop of water count. But here, too, are trade-offs, according to Ray Hoffaker, an economist at Washington State University. He warns that when a farmer uses a water allocation more efficiently, it can rob downstream water users. He points to northern Idaho, where farmers replaced flood irrigation with high efficiency sprinklers. The change produced more food per hectare with less water. But it also created an unexpected crisis, what Hoffaker calls "an invisible drought."
He explains that the run-off water from the flood irrigation was never really wasted. "What happened was, [it] was filtering down, recharging the aquifer. The aquifer was charging springs. And now since the switch to the higher efficiency systems … the cities relying on that spring water are now not able to fill their rights, dairies are not able to fill their rights. Fisheries are not able to fill their rights. The Idaho legislature is having to appropriate $ 3 million a year to buy new water to fund the water usage in Southern Idaho."
That's why many western states, including Colorado, strive to control consumptive water use. For instance, if a farmer switches to more efficient irrigation, using less of his allocated water, most states will not allow him to sell that leftover water to another user, such as a city… reducing any economic incentive to become more efficient.
But some farmers may have no choice but to increase efficiency. As the needs of downstream users become more apparent, some irrigation water has been diverted. That's what happened recently to many Colorado farmers whose irrigation wells were approved half a century ago. Because these wells have reduced the flow in Colorado rivers, the state has ordered hundreds of them to be shut off.
In much of the West, the longer someone's had a water allocation, the more likely it is that they can hang onto it. So, as a third generation operation with water rights that date to the 1850s, Petrocco Farms has not been part of these massive shut-offs. But as a truck brings in a tractor to help with the new spring plantings, Dave Petrocco worries about the future of farming in Colorado. "Every year in our area, here in Colorado, there are fewer farmers." He says that for the sake of growing crops, and also serving communities, it's important to keep looking for ways that everyone can do more, with less water.