Much of Painter’s work has focused on how dust affects river runoff, particularly on the eastern half of the Colorado River Basin. It’s critical work because the river and its tributaries account for nearly 75 percent of the regional water supply. Water from the Colorado River irrigates almost 5.5 million acres (2.2 million hectares) of land, accounting for about 15 percent of U.S. food crops and 13 percent of U.S. livestock. Nearly 40 million people in seven states and northern Mexico depend on the river to quench their agricultural, industrial, and everyday thirsts.
“People in Denver, Phoenix, Los Angeles, San Diego, Las Vegas...they all have their straws in this river,” Painter says. “Forecasting runoff affects everything from reservoirs to water managers to U.S. relations with Mexico.”
The dust and snowmelt problem has been growing for quite some time in the American Southwest. According to studies of sediments at the bottom of lakes in Colorado’s San Juan Mountains, airborne dust significantly increased in the mid-1800s as settlers stopped crossing the Plains and Rockies and started putting down roots. By 1890, airborne dust was about five to seven times greater than before American settlement.
While grazing animals likely created the initial dust loads, water extraction has become a modern culprit. In the 20th century, groundwater pumping increased dramatically, lowering the water table and further drying the soil. Modeling studies by Painter’s group have suggested that annual snow runoff in the Colorado River watershed today is lower by more than five percent compared to pre-settlement levels.
“Even if dust disturbance stabilizes and there’s no ongoing trend, we may have gone into a new regime in which snowpack gets dirtier earlier and melts off sooner,” Painter says. In places like Colorado, that will mean a shortened ski season, and all the attendant economic consequences. For the tens of millions of people who rely on the Colorado River for water, supplies will drop. And the shrinking of Earth’s snowy white insulation will mean less sunlight is reflected back into space and more heat is retained near the surface.
Painter looks to history for hope. “In the 1930s, we had the Dust Bowl. It was a climatic event, but it was made worse by land-use practices in which the farmers were unwittingly abusing the land,” he says. “The story goes that when Congress was arguing over the Dust Bowl, one of these big storms deposited a centimeter of dust on the steps of the U.S. Capitol. That was what was needed to convince them, and they took action.”
The Taylor Grazing Act of 1934 changed how public lands could be used for livestock. Studies of lake sediments have suggested that the amount of dust falling in the Rocky Mountains dropped by about one quarter after that.
“Those regions are far more stable today, and they don’t emit as much dust,” Painter notes. “When disturbed lands have been allowed to recover, there’s a drop in dust emission. So can something be done?”
