Influence of winter season climate variability on snow-precipitation ratio in the western United States

Abstract

In the western United States, climate warming poses a unique threat to water and snow hydrology because much of the snowpack accumulates at temperatures near 0 °C. As the climate continues to warm, much of the region's precipitation is expected to switch from snow to rain, causing flashier hydrographs, earlier inflow to reservoirs, and reduced spring and summer snowpack. This study investigates historical variability in snow to precipitation proportion (S_f) and maps areas in the western United States that have demonstrated higher S_f sensitivity to warming in the past. Projected changes in S_f under 1.1, 1.8, and 3.0 °C future warming scenarios are presented in relation to historical variability and sensitivity. Our findings suggest that S_f in this region has primarily varied based on winter temperature rather than precipitation. The difference in S_f between cold and warm winters at low- and mid-elevations during 1916-2003 ranged from 31% in the Pacific Northwest to 40% in the California Sierra Nevada. In contrast, the difference in S_f between wet and dry winters was statistically not significant. Overall, in the northern Sierra, Klamath, and western slopes of the Cascade Mountains Ranges, S_f was most sensitive to temperature where winter temperature ranged between -5 to 5 °C. Results from our trend analysis show a regional shift in both S_f and signal-to-noise ratios during 1960-2003 as compared with 1916-2003. Our findings indicate that natural variability in S_f over 1916-2003 across all regions except for the Great Basin most closely resembles the projected 2040-warming scenario (+1.8 °C).

Citation

Safeeq, Mohammad; Shukla, Shraddhanand; Arismendi, Ivan; Grant, Gordon E.; Lewis, Sarah L.; Nolin, Anne. 2015. Influence of winter season climate variability on snow-precipitation ratio in the western United States. International Journal of Climatology. doi:10.1002/joc.4545.