Illuminating Snow Droughts: The Future of Western United States Snowpack in the SPEAR Large Ensemble
Journal
Journal of Geophysical Research: Atmospheres
Journal Volume
129
Journal Issue
10
Start Page
e2023JD039754
ISSN
2169-897X
2169-8996
Date Issued
2024-05-28
Author(s)
DOI
10.1029/2023JD039754
Abstract
Seasonal snowpack in the Western United States (WUS) is vital for meeting summer hydrological demands, reducing the intensity and frequency of wildfires, and supporting snow-tourism economies. While the frequency and severity of snow droughts (SD), that is, anomalously low snowpacks, are expected to increase under continued global warming, the uncertainty from internal climate variability remains challenging to quantify with observations alone. Using a 30-member large ensemble from a state-of-the-art global climate model, the Seamless System for Prediction and EArth System Research (SPEAR), and an observations-based data set, we find WUS SD changes are already significant. By 2100, SPEAR projects SDs to be nearly 9 times more frequent under shared socioeconomic pathway 5-8.5 (SSP5-8.5) and 5 times more frequent under SSP2-4.5, compared to a 1921–2011 average. By investigating the influence of the two primary drivers of SD, temperature and precipitation amount, we find the average WUS SD will become warmer and wetter. To assess how these changes affect future summer water availability, we track late winter and spring snowpack across WUS watersheds, finding differences in the onset time of a “no-snow” threshold between regions and large internal variability within the ensemble that are both on the order of decades. We attribute the inter-regional variability to differences in the regions' mean winter temperature and the intra-regional variability to irreducible internal climate variability which is not well-explained by temperature variations alone. Despite strong scenario forcing, internal climate variability will continue to drive variations in SD and no-snow conditions through 2100.
Subjects
climate change
climate extremes
global climate model
internal climate variability
snow drought
western U.S. hydroclimate
Publisher
American Geophysical Union (AGU)
Type
journal article