Where Did the Snow Go?

High above the Hoh Rain Forest, the peaks of the Olympic Mountains catch snow all winter long. On Mount Olympus, 50 to 70 feet of snow can fall in a single year. All that snow piles into a thick winter blanket called snowpack. When summer comes, the snowpack melts slowly, sending cold water down the Hoh River, right past the mossy trees and the salmon. But scientists who measure the mountains have noticed something: the snow is shrinking.

The Hoh Rain Forest is famous for rain, about 140 inches of precipitation a year, but its river depends on something frozen. Each winter, 50 to 70 feet of snow can fall on Mount Olympus, building a deep snowpack that feeds the Blue Glacier and other ice high in the Olympic Mountains. Through the summer, that frozen storehouse melts a little at a time, keeping the glacier-fed Hoh River cold and full as it carves its way from Mount Olympus toward the Pacific Coast. Lately, though, measurements across the region show the snowpack is shrinking, and that quiet change reaches all the way down to the forest floor.

Think of snowpack as the forest's water savings account. In winter, the mountains save up water as snow. In summer, when rain is rare, the mountains spend those savings a little at a time. Scientists call snowpack a natural reservoir, which means a storage place for water. In many parts of the American West, mountain snow holds more water than the reservoirs people have built with dams. All summer long, the Hoh River makes withdrawals from this icy bank.

Snowpack works like a savings account with perfect timing. Winter storms deposit water as snow, and warming weather releases it through spring and summer, exactly when the Pacific Northwest gets the least rain. Scientists call it a natural reservoir: in many watersheds of the western United States, more water is stored in mountain snowpack than in the region's human-built reservoirs. That slow, steady melt is what keeps rivers and streams flowing through the dry months. The U.S. Geological Survey calls snowpack a "frozen reservoir," because much of the water in the western United States comes from snowmelt. When snowpack is low or melts too early, there is less water later in the year, just when rivers, forests, and fish need it most.

Scientists have measured mountain snow for a long time. Every April, when the snow is usually at its deepest, they check measuring stations all across the West. Between 1955 and 2020, spring snowpack across the American West shrank by nearly 20 percent on average. It shrank at 86 out of every 100 places they measured. Why? The climate is warming, and warmer weather melts the snow earlier. When the melt comes too soon, the savings account runs low before summer, just when the forest needs it.

Since 1955, scientists have tracked snow at measuring stations all across the West, checking each April, historically the month when snowpack reaches its peak. The trend is clear. Spring snowpack across the American West declined by nearly 20 percent on average between 1955 and 2020, and April snowpack shrank at 86 percent of the sites measured. In the Northwest states of Washington, Oregon, and Idaho, all but four stations recorded decreases. The snow is also peaking earlier in the year, by nearly eight days on average since 1982. The cause is a warming climate: as the West warms, the snowpack melts sooner, and when the melt starts and finishes early, streamflow falls out of sync with the needs of people and fish, draining the savings account before the dry season arrives.

Here is a surprise: in this famously rainy forest, summers are actually quite dry. In late summer, the Hoh River counts on melting snow and glacier ice to stay cold and full. Salmon need that cold water to survive and to spawn, which means to lay their eggs. But the ice is fading too. In 1982, scientists counted 266 glaciers in Olympic National Park. By 2009, only 184 were left. Less snow and ice can mean a lower, warmer river just when fish need it most.

Park scientists point out that in an area known for its rain, summers are actually quite dry. That is when the high country matters most: glacier runoff and snowmelt feed Pacific Northwest rivers with cold water that sustains downstream ecosystems through the dry summer and fall months. Salmon and bull trout depend on that cold flow, because water temperature shapes when fish spawn and how streams support life. Yet the frozen high country is fading. The number of glaciers in Olympic National Park fell from 266 in 1982 to 184 in 2009, and surveys found 36 more glaciers gone, an 18 percent loss of ice area, between 2009 and 2015 alone. The park calls its glaciers vital late-summer sources of water for sensitive ecosystems and species.