A cold Arctic air mass swept southward across the high plains last Tuesday, its 50 mph winds dropping temperatures by 50 degrees overnight. Blowing over drought-parched farm soil, the wind created a huge dust storm in eastern Colorado, visible in striking photographs from aircraft and from space. The same region had seven dust storms last year. In 2012, a severe dust storm caused multiple traffic accidents in northern Oklahoma.
Dust storm near Lamar, Colorado, 2013. Photo by Denver Post, permission requested.
"You hear sand and dirt pounding against the window," said Colorado farmer Dave Hixson after a 2013 storm. "You know that it’s your crop that’s hitting the windows and blowing away, and it’s not just affecting you, but also everyone else."
Wind takes nearly half the soil eroded from American farmlands. It does its worst in parts of the high plains, where agriculture is pushing its limits: eastern Colorado and nearby regions of Oklahoma and Texas, as well as North Dakota. East of the high plains, severe wind erosion affects the Red River valley of North Dakota-Minnesota. Unprotected soil blows away many times faster than it forms in these regions.
Wind and water erosion in central US, 2007, enlarged from USDA map.
Dust clouds make a spectacle, but much more happens at the soil surface. Wind rolls tiny clods along the ground to smash into other clods and release fine dust. It bounces smaller particles high in the air to impact a few feet downwind, stirring other particles and dust. The rolling and bouncing grains collect into drifts, sometimes forming dunes that can propagate downwind to smother undamaged cropland.
Wind erosion works as a sieve, removing the small particles of organic matter, loam and clay that make soil fertile and leaving a sandy, infertile residue. It can degrade the soil to plow depth in one season on an unprotected field.
Many farmers protect soil from the wind with a cover of untilled crop stubble. Sometimes they sow a cover crop in fall to protect the ground until planting time. They manage the soil’s chemistry and moisture content to make it clod better and resist wind damage. Some install various windbreak structures, from permanent grass strips to rows of blue spruce trees.
Shrub field windbreaks in Montana. Photo from KSU Wind Erosion Research Unit, permission requested.
Much of the cropland in the high plains is watered from wells, about half of them drawing on "fossil water" stored from prehistoric times in the Ogalalla aquifer. The Ogalalla has lost about 9% of its volume since 1950, as irrigated row crops have boomed. In some counties, its level is now dropping up to two feet per year. Farmers are forced to turn to less thirsty crops or grazing, or to give up irrigation altogether.
Farmers in Kansas, Texas and Colorado have been making voluntary reductions in water use to preserve the aquifer. The Natural Resources Conservation Service is promoting water conservation with its Ogalalla Initiative . But Colorado now requires farmers to comply with the state’s groundwater rules or have their wells shut down.
With dry fields and irrigation comes the risk of salinization. All ground water contains some dissolved minerals, which can build up in the soil if it dries out often. Ogalalla water can potentially cause salinization, and the risk may increase as farmers cut back on water use.
In the Red River Valley, farmers are dealing with natural salinity in the soil, made worse by recent increases in rainfall. Researchers used satellite sensors in a recent study to begin monitoring soil salinity there.
Cropland in the valley may soon be at additional risk from flood as well as drought, if the Red River Diversion project goes ahead as planned. Levees upstream of Fargo, ND will divert flood waters into local farmland, letting them drain through a 36 mile ditch around the city. South Dakota and Minnesota farmers are protesting the plan, as is the governor of Minnesota. The Red River has flooded in 49 of the last 110 years.
Severe salinization can form salt pans in the midst of cropland, as seen in this photograph from southwestern Australia:
Photo by airline passenger in southwestern Australia.
Forecasts for the next 20 to 30 years call for more frequent droughts in the U.S. southwest — overlapping the southern high plains. Droughts will be caused by climate cycles in Atlantic and Pacific water temperatures, further boosted by global warming. Some climate studies have predicted more dust storms in the region as higher temperatures damage the natural vegetation. These predictions led one science writer to warn of "dustbowlization", and probably provided some inspiration for the film Interstellar.
Agriculture stretches to the limits of available moisture here. The wave of homestead settlement washing the central states in the 19th century thinned and stopped in the western reaches of the high plains. The largest homesteads were too small to earn a living and only giant farms and ranches prospered. Groundwater irrigation, literally "water mining" in this context, sparked a boom half a century ago which now seems to be receding. And in these plains, where farming and ranching already push their limits, the limits themselves are tightening.
"Erosion of Soil by Wind," Soil: USDA Yearbook of Agriculture 1957