Climate Change – Global Drying
“It is impossible to talk about the history of human civilization without talking about water,” according to Sandra Postel, a water researcher and director of the Global Water Policy Project. In her book Pillar of Sand she asks if the irrigation miracle can last. “The story of settled agriculture, the growth of cities, and the rise of early empires is to no small degree a story of controlling water in order to make the land more prosperous and habitable.”
In the 21st century, global warming may produce a worldwide pattern of persistent droughts in some areas and floods in others. The droughts could dry up irrigation reservoirs and deplete underground aquifers. The fight over dwindling supplies could pit a tattered remnant of American farmers – who, in the first years of the century, are still producing surplus crops – against a burgeoning population of city dwellers demanding water to drink, flush their toilets and irrigate their golf courses.
In 2007, the UN’s Intergovernmental Panel on Climate Change (IPCC) reviewed the latest scientific studies and concluded that the polar areas of the world will get wetter in the next century, but the mid-latitudes – where one-sixth of world’s population lives now – will get drier. “By mid-century, annual average river runoff and water availability are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics.” These semi-arid, mid-latitude regions include much of the America West where irrigation makes possible some of the most productive farmland in the world.
The United Nations’ Food and Agriculture Organization says that “64 percent of the world’s population [is] expected to live in water-stressed [river] basins by 2025.”
Worldwide, farmers use 70 percent of the freshwater that is used by humans. In places like Colorado, that percentage goes up to 90 percent.
Water managers draw differences between “consumptive and nonconsumptive” uses of water. Roughly, consumptive uses include those when water is taken from a reservoir or underground aquifer that can’t be recovered. In agriculture, the vast majority of water is consumed, or used consumptively, because water put on fields will eventually evaporate or transpire from crops into the atmosphere. Evaporated water may fall as rain 1,000 miles away – that’s how the Earth’s water cycle works – but it’s gone locally.
Most water used by cities is not consumed because it’s captured by sinks and drains, cleaned up by the city’s sewer and waste treatment facilities and dumped back into local rivers. At least one city in Colorado, Aurora, is building a system that will draw water from the banks of the South Platte River, filter it through the naturally occurring sand and gravel around the river and further purify it before it goes into the drinking water supply. The trick is that the South Platte is the same river that Aurora uses to carry away the water citizens have “used” once already. Treated wastewater is dumped into the South Platte miles upstream from where Aurora’s new pumping system is collecting the water. In a sense, Aurora is recycling its wastewater, a fact that they don’t advertise a lot. This is a “closed-loop” system that will continually clean and recycle the water in the city’s system.
The system is an innovative and, in one sense desperate, approach to water scarcity, and it’s a measure of how critical water is to the American West.
Colorado water is critical because the snows that fall on the Rocky Mountains melt and feed streams and rivers that supply at least five other states with much of their surface water — California, Nevada, Arizona, Kansas and Nebraska. Since legal compacts were first worked out in the 1920s, there have been a series of disputes between these states over who should get how much water.
Agriculture is in the middle of these disputes because so much of the food supply is made possible by irrigation. We now get about 40 percent of our food from irrigated land worldwide.
In Colorado, irrigation consumes as much as 90 percent of the water left in the state, yet the number one industry in the state is tourism. The state has gone from fur-trapping, to mining, to farming, to manufacturing and an urban-centered economy.
In Nebraska, irrigation is even more critical. In 2007, the state became the leader in the number of irrigated acres with 8.56 million acres being watered artificially. That surpasses California with 8.02 million, Texas with 5 million, Colorado with 2.87 million and Kansas with 2.76 million acres in irrigation. Nebraska is also the home state for the world’s four leading center pivot manufacturers.
Yet, dropping water tables and disputes with other states has led Nebraska close to the point of outlawing any additional irrigation wells and paying other farmers not to turn on their existing wells.
Heather Derr (left) thinks that despite how much water farmers use, they are getting a bad rap. “I think farmers as a whole do an excellent job of conserving,” she says. “Foot for foot, I’ll bet [urban] lawns are watered much more than our crops are watered. And yet, we get the blame for lowering the water table.”
In this section, we’ll consider why researchers have concluded that global warming will change weather patterns, how environmental concerns are constricting irrigation practices and how the competing needs of food production, human use, recreation and the environment will sort out water use in the 21st century.