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Article
Open Access
Published: 02 March 2018
Dramatic declines in snowpack in the western US
Philip W. Mote

, Sihan Li, Dennis P. Lettenmaier, Mu Xiao & Ruth Engel
npj Climate and Atmospheric Science
volume
1, Article number: 2 (2018) Cite this article
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Abstract
Mountain snowpack stores a significant quantity of water in the western US, accumulating during the wet season and melting during the dry summers and supplying much of the water used for irrigated agriculture, and municipal and industrial uses. Updating our earlier work published in 2005, we find that with 14 additional years of data, over 90% of snow monitoring sites with long records across the western US now show declines, of which 33% are significant (vs. 5% expected by chance) and 2% are significant and positive (vs. 5% expected by chance). Declining trends are observed across all months, states, and climates, but are largest in spring, in the Pacific states, and in locations with mild winter climate. We corroborate and extend these observations using a gridded hydrology model, which also allows a robust estimate of total western snowpack and its decline. We find a large increase in the fraction of locations that posted decreasing trends, and averaged across the western US, the decline in average April 1 snow water equivalent since mid-century is roughly 15–30% or 25–50 km3, comparable in volume to the West’s largest man-made reservoir, Lake Mead.
Introduction
California’s recent multi-year drought (2011–16) and its extension into Oregon and Washington has shown that warming can create drought simply by preventing the accumulation of mountain snowpack. The year 2015, for instance, set the record low 1 April snow water equivalent (SWE) at over 80% of sites west of 117° longitude,1 a result of high winter temperatures rather than low precipitation.2,3,4
More than a decade ago, we showed that spring snowpack had declined at a large majority of locations in the mountainous western US, and corroborated the observations with hydrologic modeling that reached broadly similar conclusions.5 We also noted that computing an area-averaged snowpack value from observations is challenging because the locations of long-term monitoring sites are usually chosen to favor a certain type of terrain and elevational range, with temperature-sensitive locations undersampled early in the record in some states.6 Methodological choices (e.g., about record length) can therefore strongly influence results and must be carefully evaluated. In contrast, model-based estimates provide a basis for estimating long-term SWE changes across the entire Western U.S. domain.
Since our earlier work, several papers have further explored the relationships between mountain snowpack, variability and trends in precipitation and temperature, and geographically important factors. Stoelinga et al. (ref. 7) derived a snowpack index for the Cascades from streamflow measurements, from which they estimated that the spring snowpack declined 23% between 1930 and 2007. Pierce et al. (ref. 8) using a hydrologic model forced by observations and by two 1600-year climate model runs to estimate natural internal climate variability, attributed declines in snowpack (specifically SWE divided by accumulation-season precipitation) across the western US to anthropogenic warming.
Luce et al. (ref. 9) postulated that decreases in westerly winds aloft may have contributed to orographically induced decreases in high-elevation precipitation and snowpack in the Northwest, which the sparse high-elevation observations might not detect. Our previous work found little to no decrease at high elevations, but large decreases at low elevations,5,10 whereas their mechanism would produce the opposite. Nonetheless, the wind-induced changes join other factors besides direct anthropogenic warming in potentially influencing regional snowpack.
Changes in vegetation cover in or near snow courses, as well as station moves, could lead to spurious or non-climatic trends. Unfortunately, scant evidence is available about changes in vegetation over time at snow course locations. In a rare exception, Julander and Bricco (ref.11) compare recent photographs of snow courses in Utah with photographs from 1936, noting that in some locations there was no change in vegetation while in others there was a complete transformation owing, e.g., to logging or fire. Such changes have been shown to affect significantly the accumulation and ablation rates, and could be as large as climate-driven trends. Julander and Clayton (ref. 12) in a study of 15 Utah snow courses (all but one at >2200 m elevation) noted that SW

Germany's harvest of "ice wine" (a rather sweetdessert wine produced from grapes that have frozen while still on the vin) has failed for the first time ever because the winter has been too warm.

"The 2019 vintage will go down in history here in Germany as the first year in which the ice harvest has failed nationwide," the German Wine Institute (DWI) said in a statement.

"If the warm winters continue in the next few years, ice wines from German wine regions will soon become even more of a rarity than they already are," said Ernst Büscher from the DWI.

Another problem for ice wine production is that, in recent years, the dates for a possible ice harvest have shifted later - to January and February - while the grapes are ripening earlier, the DWI said.
As a result, the grapes need to survive for longer.

Press release DWI

Snowpack is in fact declining.

No cherry picking.

No suppression of data.

Just an oralloy/ denialist red herring.

Oh you mean some ten-year-old controversy about one single article is all you've got?

Millions of papers have been published since. Look at the forest, not at the tree.

Oralloy alleges that there has been "cherry-picking" of data, but he doesn't say what data, nor does he name the names of those involved in this putative deceit.

It's you who are wrong,

The cherry picking and suppression of facts has been exposed for all to see.