How the last 20 years of Sierra snowpack stack up, in one graphic

The Sierra snowpack has reached its seasonal peak.

The snowpack plays an important role in providing water to millions of Californians. Throughout the winter months, snow accumulates on the high peaks of the Sierra Nevada and slowly melts in the spring and early summer. The runoff fills dozens of major reservoirs downstream.

Last year’s epic snowpack helped relieve a yearslong drought, reaching an eye-popping 252% of normal on April 8. By that date, the mountains held an average equivalent of 64.2 inches of water.

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The current snowpack now holds a healthy 28.6 inches of water on average after a series of winter storms alleviated concerns that California was facing a “snow drought.”

The California Department of Water Resources tracks the snow water equivalent in the Sierra using a network of 130 electronic sensors. The system went online in 1990s and began producing daily data in the early 2000s. Before that, officials relied on monthly snow surveys to measure the snowpack.

This graphic plots a 20-year history of the Sierra snowpack, showing wet years interspersed with severe droughts.

When stacked up, the last two decades reveal California’s quintessential pattern of bust and boom. When California faces long dry spells, it takes large amounts of snow and rain to reverse the trend.

This cycle is projected to become more extreme as the planet warms. With human-caused climate change, higher temperatures are intensifying droughts, and the state’s average snowpack is projected to shrink significantly as temperatures continue to climb.

Tracking the rise and fall of California’s snowpack over the past two decades provides a long-term view of the state’s highly variable climate and the patterns that dictate our water fortunes.