Climate Change Impacts on Snowstorms and implications for Skiing in California

Technical Summary: Climate Change Impacts on Snowstorms and Implications for Skiing in California

Problem Statement
Climate change is altering global precipitation patterns, with snowfall being particularly sensitive to temperature shifts. While increased heavy precipitation is projected, the phase of precipitation (solid vs. liquid) is expected to shift toward rain, posing significant risks to snow-reliant ecosystems and economies. In the western United States, specifically California's Sierra Nevada, winter recreation and regional water resources depend heavily on snowfall. However, existing research often focuses on climatological averages rather than individual storm events. There is a need to understand how specific extreme snowstorms, which drive both economic benefits (ski season duration) and hazards (infrastructure damage, avalanches), will evolve under future warming scenarios. This study addresses the gap in storm-specific analyses for the U.S. West Coast to quantify how future warming influences extreme snowfall events and the subsequent implications for the ski industry.

Methodology
The study employs the Pseudo-Global Warming (PGW) framework to isolate the thermodynamic effects of climate change on two distinct historical snowstorms that impacted California in late February/early March of 2023 and 2024.

• Modeling: The Weather Research and Forecasting (WRF) model (version 4.1.2) was used with a two-way nested domain configuration (9 km outer, 3 km inner) to resolve topographic influences on precipitation.
• Experimental Design: Simulations were conducted for four climate epochs: the 1850s (pre-industrial), the present day (historical storm conditions), the 2070s (near-future), and the 2090s (far-future). Future perturbations were derived from the SSP2-4.5 scenario using the multi-model mean of 11 CMIP6 datasets.
• Ensemble Approach: To account for uncertainty in cloud microphysics, three different microphysics schemes (Morrison 2-Moment, Thompson Graupel, Goddard 4-Ice) were averaged for each storm and climate period, resulting in 12 ensemble simulations per storm.
• Validation: Model performance was validated against the SNODAS (Snow Data Assimilation System) gridded dataset and 40 SNOTEL (Snowpack Telemetry) stations, focusing on total, solid, and liquid precipitation.
• Analysis: The study quantified changes in Integrated Vapor Transport (IVT), precipitation phase (rain vs. snow), and total precipitation amounts across the study domain and specifically at 69 ski resort locations within the region.

Key Results

• Model Validation: The WRF model adequately reproduced precipitation patterns, though it exhibited a slight cold bias, placing the snowline at lower elevations than observed. Relative biases for total precipitation were 17.6% (vs. SNODAS) and 25.5% (vs. SNOTEL), with RMSE values comparable to previous studies.
• Precipitation Phase Shift: A significant phase shift was observed in future simulations. Across the study region, liquid precipitation increased by an average of 12.43% in the 2090s, while solid precipitation decreased by 8.37%.
  • 2023 Storm (Cold): This unusually cold event remained predominantly solid even in future scenarios. Ski resorts experienced increases in total and solid precipitation with minimal change in liquid precipitation, suggesting that extreme cold events may still produce heavy snowfall despite warming trends.
  • 2024 Storm (Warmer): This more typical storm showed a pronounced shift. Future simulations indicated substantial increases in liquid precipitation and decreases in solid precipitation at ski resort elevations, with the snowline rising significantly.
• Spatial Distribution and Moisture Transport:
  • Inland Shift: For the 2023 storm, future periods showed a shift of precipitation inland, with decreases at coastal low elevations and increases over the Sierra Nevada. This shift was attributed to increased atmospheric stability suppressing coastal convection while orographic lift enhanced inland precipitation.
  • Northward Shift: For the 2024 storm, IVT strength increased, particularly in northern California, causing a northward displacement of the storm track.
• Total Precipitation: Total precipitation increased slightly on average (2.8% across both storms) in the 2090s, driven by enhanced atmospheric moisture capacity (Clausius-Clapeyron effect).

Significance and Claims
The paper claims that the impact of climate change on extreme winter storms is not uniform but is strongly dependent on the initial thermodynamic characteristics of the storm.

• Storm-Specific Sensitivity: Colder storms may retain or even increase snowfall intensity due to higher atmospheric moisture, whereas warmer storms are highly sensitive to small temperature increases, leading to a rapid transition from snow to rain at ski resort elevations.
• Implications for the Ski Industry: The findings suggest a dual risk for the Sierra Nevada ski industry. While some cold, extreme events may continue to produce heavy snow (potentially causing closures due to buried infrastructure or avalanches), warmer storms will increasingly result in rainfall at resort elevations. This transition threatens the long-term viability of winter recreation by reducing snowpack, accelerating melt, increasing avalanche risk, and shortening the ski season.
• Hydrological and Hazard Management: The study highlights that future winter hazards will be driven by changes in precipitation phase and spatial distribution (inland and northward shifts) rather than a simple uniform reduction in snowfall. This necessitates storm-specific analyses for improving water resource management, flood risk assessment, and infrastructure planning in a warming climate.

The authors conclude that while extreme snowfall hazards may persist, the character of these events is shifting, with warmer storms posing a greater threat to the snow reliability required for the region's winter tourism economy.