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Tuesday, September 21, 2010

Thomas H. Painter et al., PNAS (2010), Response of Colorado River runoff to dust radiative forcing in snow

Proceedings of the National Academy of Sciences, published online before print September 20, 2010; doi:10.1073/pnas.0913139107

Response of Colorado River runoff to dust radiative forcing in snow

  1. Thomas H. Paintera,b,*
  2. Jeffrey S. Deemsc,d
  3. Jayne Belnape,
  4. Alan F. Hamletf
  5. Christopher C. Landryg and 
  6. Bradley Udalld
  1. aJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109;
  2. bJoint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095;
  3. cNational Snow and Ice Data Center, Boulder, CO 80309;
  4. dNational Oceanic and Atmospheric Administration Western Water Assessment, Boulder, CO 80309;
  5. eUnited States Geological Survey, Southwest Biological Center, Moab, UT 84532;
  6. fUniversity of Washington, Department of Civil and Environmental Engineering, Seattle, WA 98195; and
  7. gCenter for Snow and Avalanche Studies, Silverton, CO 81433
  1. Edited by Peter H. Gleick, Pacific Institute for Studies in Development, Environment, and Security, Oakland, CA, and approved August 3, 2010 (received for review November 12, 2009)


The waters of the Colorado River serve 27 million people in seven states and two countries but are overallocated by more than 10% of the river’s historical mean. Climate models project runoff losses of 7–20% from the basin in this century due to human-induced climate change. Recent work has shown however that by the late 1800s, decades prior to allocation of the river’s runoff in the 1920s, a five-fold increase in dust loading from anthropogenically disturbed soils in the southwest United States was already decreasing snow albedo and shortening the duration of snow cover by several weeks. The degree to which this increase in radiative forcing by dust in snow has affected timing and magnitude of runoff from the Upper Colorado River Basin (UCRB) is unknown. Here we use the Variable Infiltration Capacity model with postdisturbance and predisturbance impacts of dust on albedo to estimate the impact on runoff from the UCRB across 1916–2003. We find that peak runoff at Lees Ferry, Arizona, has occurred on average 3 wk earlier under heavier dust loading and that increases in evapotranspiration from earlier exposure of vegetation and soils decreases annual runoff by more than 1.0 billion cubic meters or ∼5% of the annual average. The potential to reduce dust loading through surface stabilization in the deserts and restore more persistent snow cover, slow runoff, and increase water resources in the UCRB may represent an important mitigation opportunity to reduce system management tensions and regional impacts of climate change.


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