Sierra Nevada Snowpack

Sierra Nevada Snowpack Analysis

100-Year Historical Data | Water Supply for Sacramento, Lodi & Stockton

28.2"

Baseline SWE (1925-50)

-30%

2010s vs Baseline

5%

2015 Record Low (% Avg)

Sierra Nevada Watersheds - Snowpack Change

Effective Water Storage Decline

(SWE + timing + coverage factors)

-50% or more (Severe)

-35% to -50% (High)

-20% to -35% (Moderate)

0% to -20% (Low)

Historical Snowpack Data by Decade

Decades All Years

Baseline (1925-1950 avg): -- in SWE

🟢 Baseline decades SWE = Snow Water Equivalent (inches of water in snowpack)

20-Year Trends: SWE & Snowmelt Timing

Baseline Period (1925-1944)

Mid-Century

Recent (2005-2025)

What is SWE?

Snow Water Equivalent (SWE) measures the amount of liquid water contained in the snowpack, expressed in inches. Unlike snow depth, SWE accounts for snow density—wet, heavy snow has more water than dry, fluffy snow. April 1st SWE is the standard benchmark used to forecast summer water supply.

Baseline: 1925-1950

The baseline average SWE is 28.2 inches (1925-1950 average). Map shading shows effective water storage decline, which combines lower SWE, earlier snowmelt timing, rising snow levels, and reduced snow-covered area—not just peak SWE values.

Key Findings

The 2015 snowpack was unprecedented in 500 years of reconstructed data. The period from 2000-2018 was the driest since the late 1500s. Snow levels have risen 700+ meters since 2008, dramatically reducing snow-covered area.

Water Supply Impact

Sierra Nevada snowpack provides 30% of California's water supply. The American, Mokelumne, and Stanislaus Rivers supply water to Sacramento, Lodi, and Stockton respectively.

Data Sources

SWE data from CA Dept. of Water Resources snow surveys (since 1930), tree-ring reconstructions (pre-1930), and UC Berkeley Central Sierra Snow Lab. Map decline % includes timing and coverage factors from NASA/NOAA research.

Climate Outlook

With 1.5°C warming, odds of below-average snowpack increase by 30%+. More precipitation is falling as rain instead of snow, and snowmelt is occurring 2-4 weeks earlier than in the 1950s.

Data sources: California Department of Water Resources, UC Berkeley Central Sierra Snow Lab, NASA Earth Observatory, NOAA NCEI | CDEC | CSSL | Created for Lodi411.com