Which Way Will the Dust Blow?

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.”

Map of the Uppaer Colorado River Basin.
The Upper Colorado River Basin encompasses parts of six western states. Green indicates forest, while beige indicates scrub or barren areas. Yellow regions are pasture, cropland, or grassland; purple areas are urban. (NASA map by Robert Simmon, using data from the National Land Cover Database.)

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?”

  1. References

  2. Field, J.P, Belnap, J., Breshears, D.D., Neff, J.C., Okin, G.S., Whicker, J.J., Painter, T.H., Ravi, S., Reheis, M.C., Reynolds, R.L. (2010) The ecology of dust, Frontiers in Ecology and the Environment, 8(8), 423-430.
  3. Intergovernmental Panel on Climate Change (2007) FAQ 4.1 Is the Amount of Snow and Ice on the Earth Decreasing?
  4. Lawrence, C.R., Painter, T.H., Landry, C.C., Neff, J.C. (2010) Contemporary geochemical composition and flux of aeolian dust to the San Juan Mountains, Colorado, United States. Journal of Geophysical Research, 115, G03007.
  5. Meko, D., et al., (2007) Medieval drought in the upper Colorado River Basin, Geophysical Research Letters, 34, L10705.
  6. Neff, J.C., Ballantyne, A.P., Farmer, G.L., Mahowald, N.M., Conroy, J.L., Landry, C.C., Overpeck, J.T., Painter, T.H., Lawrence, C.R., Reynolds, R.L. (2008) Increasing eolian dust deposition in the western United States linked to human activity. Nature Geoscience, 1, 189-195.
  7. Painter, T.H., Barrett, A.P., Landry, C.C., Neff, J.C., Cassidy, M.P., Lawrence, C.R., McBride, K.E., Farmer, G.L. (2007) Impact of disturbed desert soils on duration of mountain snow cover. Geophysical Research Letters, 34, L12502.
  8. Painter, T.H., Bryant, A.C., Skiles, S.M. (2012) Radiative forcing by light absorbing impurities in snow from MODIS surface reflectance data. Geophysical Research Letters, 39, L17502.
  9. Painter, T.H., Deems, J.S., Belnap, J., Hamlet, A.F., Landry, C.C., Udall, B. (2010) Response of Colorado River runoff to dust radiative forcing in snow. PNAS, 107(40), 17125-17130.
  10. Painter, T.H., Skiles, S.M., Deems, J.S., Bryant, A.C., Landry, C.C. (2012) Dust radiative forcing in snow of the Upper Colorado River Basin: 1. A 6 year record of energy balance, radiation, and dust concentrations. Water Resources Research, 48(7), 48, W07521.
  11. Steltzer, H., Landry, C., Painter, T.H., Anderson, J., Ayres, E. (2009) Biological consequences of earlier snowmelt from desert dust deposition in alpine landscapes. PNAS, 106(28), 11629-11634.
  12. Steenburgh, W.J., Massey, J.D., Painter, T.H. (2012) Episodic dust events of Utah’s Wasatch Front and adjoining region. Journal of Applied Meteorology and Climatology, 51, 1654-1669.
  13. U.S. Department of the Interior Bureau of Reclamation (2012, December) Colorado River Basin Water Supply and Demand Study.
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