Is It Getting Dustier in Northern Utah?

People frequently ask me if there has been a recent increase in dust storms over northern Utah.  This is actually a difficult question to answer because nobody has been directly measuring atmospheric dust concentrations for more than a few years.  As a result, we need to piece together what we can using what evidence is available.

For long-term trends, our best evidence comes from cores taken from alpine lakes.  These cores allow us to infer accumulation rate and composition of sediments going back for many centuries. Cores collected in alpine lakes in the San Juan Mountains of Colorado show a dramatic increase in dust accumulations beginning in the late 1800s. 

Sediment and mass accumulation rates from Porphyry Lake,
San Juan Mountains, CO.  Source: Neff et al. (2008).

Cores from alpine lakes in the Uinta Mountains show similar trends (see Reynolds et al. 2009).  This evidence, combined with analysis of the sediment composition, supports the conclusion that there was a significant increase in dust arising from land disturbance following the western settlement of the United States in the late 1800s.  Such land disturbance includes agricultural and livestock grazing, mining, and other activities.  There is some evidence of a decline in dust accumulation after the 1930s, possibly related to the enactment of the Taylor Grazing Act of 1934, although accumulation rates remain far higher than occurred before western settlement.  

These lake cores, however, don't allow us to examine the frequency and characteristics of individual dust storms and how they change from year to year and decade to decade.  To get at such fine-scale details, one option is to use hourly surface observations from the Salt Lake City International Airport, which provides a nearly continuous record back to 1930.  That sounds great, but there are challenges with using this record, including inconsistencies in reporting practices and observer biases, coding and translation errors, and changes in instrumentation, reporting guidelines, and processing algorithms.   Keep these limitations in mind as we plow forward.

The number of dust events reported at the Salt Lake City Airport does show an over decline since 1930, with large ups and downs from year to year.  A relatively small number of events were reported around water year 2000 (the water year is October to September), with a greater frequency of events since that time.  

Source: Steenburgh et al. (2012)

At issue with such an analysis, however, is that it doesn't account for event intensity.  One big event have a huge impact on dust accumulations.  Without direct dust observations, we are forced to improvise and use visibility as a proxy for dust concentration.  If we do this, and consider the strength of the winds, we can estimate the total flux of dust each water year at the Salt Lake City Airport.  This shows even larger year-to-year variations since intense events are less common but have a huge impact on the total dust flux.  Nevertheless, there is some downward trend with the minimum apparent again around water year 2000.

Source: Steenburgh et al. (2012)

Now is the time to inject some word of caution.  Recall some of the issues at play in this dataset.  When combined, however, with the alpine lake core data, it is probably safe to say that overall dust accumulations are somewhat lower today then they were in the 1930s.  If we could freeze the current climate and land-use conditions, we'd probably see ups and downs from year to year and decade to decade similar to those since the 1970s.  The future, however, will depend largely on land-use management, water-resource management, and climate variability and change.  

It is worth noting that dust emissions are not equal across the Great Basin.  The image below shows the approximate origins (plus signs) and orientations (colored lines) of major dust plumes identified in satellite imagery western Utah, Nevada, and southern Idaho.  

Source: Steenburgh et al. (2012)

It is possible that the lowest hanging fruit for reducing the frequency and intensity of wind-borne dust events would be to target these areas of dust emissions.