Identifying Coherence Across End-of-Century Montane Snow Projections in
the Western United States
Abstract
Montane snowpack is a vital source of water supply in the Western United
States. However, the future of snow in these regions in a changing
climate is uncertain. Here, we use a large-ensemble approach to evaluate
the consistency across 124 statistically downscaled snow water
equivilent (SWE) projections between end-of-century (2076 – 2095) and
early 21st century (2106 – 2035) periods. Comparisons were performed on
dates corresponding with the end of winter (15 April) and spring
snowmelt (15 May) in five western US montane domains. By benchmarking
SWE climate change signals using the disparity between snow projections,
we identified relationships between SWE projections that were repeatable
across each domain, but shifted in elevation. In low to mid-elevations,
15 April average projected decreases to SWE of 48% or larger were
greater than the disparity between models. Despite this, a significant
portion of 15 April SWE volume (39 – 93%) existed in higher elevation
regions where the disparities between snow projections exceeded the
projected changes to SWE. Results also found that 15 April and 15 May
projections were strongly correlated (r 0.82), suggesting that
improvements to the spread and certainty of 15 April SWE projections
would translate to improvements in later dates. The results of this
study show that large-ensemble approaches can be used to measure
coherence between snow projections and identify both 1) the
highest-confidence changes to future snow water resources, and 2) the
locations and periods where and when improvements to snow projections
would most benefit future snow projections.