Influence of Windblown Dust on

Snowmelt Timing in the Rocky

Mountains, USA

David W. Clow1

Mark Williams2

George Ingersoll1

1. U.S. Geological Survey

2. University of Colorado, Boulder

Using Calcium as an indicator of dust

Snowmelt is Occurring Earlier

In Colorado, Snowmelt

and Streamflow are

Ocurring 2 Weeks Earlier

than in the Late 1970s

What are the Drivers?

Clow (2010), J. Climate

Trend in Snowmelt Onset

Dust is One Driver of Early Melt

Dust changes snowpack albedo

Other Drivers Include:

Increasing Air Temperature

Decreasing Snowfall

Photo from Niwot Ridge, spring 2006

Key questions:

What is the Spatial Pattern

of Dust Deposition in the

Rocky Mountains?

Are there trends in Dust

Deposition?

What is the Relative

Importance of Dust in

Controlling Snowmelt

Timing?

Problem: Data are Sparse

Little dust data for Rocky

Mountains

Makes analysis of the

influence of dust on

snowmelt timing

problematic

Can We Take Advantage of Existing Snow

Chemistry Data?

Dust contains Calcite

Calcite dissolves readily,

releasing Ca and HCO3

(alkalinity)

Reflected in precipitation

Chemistry

Hypothesis: Calcium can be Used as Indicator of Dust Deposition

Rocky Mountain Snowpack has Chemical

Signature of Calcite

57 Sites Sampled Annually

in Rockies during 1992-

2009

PCA identified the

following components:

Alk, Ca, Mg (dust)

NH4, NO3, SO4 (acids)

Na, Cl (salt)

Explained 75% of

Variance in Chemistry

1 2 3

Alk 0.77 0.16 0.33

Ca 0.82 -0.27 0.27

Mg 0.79 -0.35 0.23

Na 0.17 -0.15 0.92

K 0.69 -0.02 -0.04

NH4 -0.13 -0.69 0.13

Cl

0.21 -0.05 0.90

NO3 0.24 -0.85 0.08

SO4 0.22 -0.88 -0.01

Principal

Components

Dusty Snow Layers Contain Calcite

Major dust event in February 2006

Dust Layer was Sampled at 14 Sites in Colorado

Samples Analyzed for Ca, Alkalinity, Dust

Concentrations

Dust Layers had a Strong Calcite Signature

Feb 2006 dust layer, Niwot Ridge

Dust often Originates in Desert Southwest

Typical Transport Trajectory

Feb 14 - 15, 2006

Spatial Patterns: Wet Deposition of Calcium

2007

Spatial Patterns: Snowpack Ca Increases

from North to South

1992-2009

averages

Alk and Mg

show same

pattern

Ca can be

used as

surrogate for

dust

Winter

Trends in Winter Ca during 1992 - 2009

Trends were

Analyzed using

the Regional

Kendall Test

(RKT)

60% of groups

had significant

trends (all up)

Trends were

Strongest in

South-Central

Rockies

Winter

Trends in Springtime Ca in Wet Deposition

Relatively few

Significant trends

A few Upward

Trends in Northern

Colorado

Climate and Dust Affect

Snowmelt Timing

Snowmelt Onset Snowmelt Center of Mass

Conclusions Dust deposition increases from north to

south in the Rockies

Trends in Dust Deposition were variable

Increasing trends in northern

Colorado, but magnitude uncertain

Major Drivers of Snowmelt Timing in the

Rockies include:

Increasing Springtime Air

Temperatures

Decreasing Snowfall

Increasing Dust Concentrations

Acknowledgements

Funding Provided by

USGS Office of Global Change

Water, Energy, and

Biogeochemical Budgets

program

National Science Foundation

Long-Term Ecological Research

program

Future Directions

Prepare Manuscript

Incorporate Dust Effect in

Hydrological Models

(PRMS)