Less snow is the new norm for the Pacific Northwest — The #LaGrande Observer

Map of the Columbia River watershed with the Columbia River highlighted. By Kmusser – self-made, based on USGS and Digital Chart of the World data., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3844725

From The LaGrande Observer (Nathan Gilles):

In 2020, Oregon experienced some of its driest conditions on record. And yet, despite the overall lack of precipitation, the state’s mountains received more or less normal amounts of snow.

However, above-average spring temperatures melted mountain snow several weeks earlier than normal in several Oregon basins. This led to water flushing through local rivers and streams before it could be used for irrigation during the late spring and summer growing seasons. As temperatures continued to rise throughout the summer, water shortages and drought declarations followed.

Around the same time Oregon farmers were watching their water drain away, a May 2020 study published in the UK-based scientific journal Nature Climate Change literally put the Columbia River Basin on the world map as a watershed whose dependence on snow for irrigation places it on the losing side of climate change.

Here, too, the reason had to do with rising temperatures and melting snow, and here, too, the point was hammered home. The study concluded that under future warming, the Columbia River Basin, the Pacific Northwest’s largest hydrologic basin, is likely to lose so much mountain snow it will experience about the same degree of water scarcity as the Middle East basin containing the Tigris River and Euphrates River. In fact, the Columbia River Basin actually comes out looking a little worse off than the Tigris/Euphrates Basin, according to the study.

Less snow, more problems

Titled “Agricultural risks from changing snowmelt,” the study outlines two ways rising temperatures are expected to lead to water shortages in the future.

In the first condition, snow will accumulate more or less as normal, but melt early due to abnormally warm temperatures, as happened this year in some Oregon basins.

In the second condition, especially warm temperatures will cause precipitation to fall mostly as rain rather than as snow, as happened region-wide during the Northwest’s “snow drought” of 2015.

Study co-author John Abatzoglou, a University of California Merced associate professor in Management of Complex Systems, says more rain and less snow is going to be the new normal as our regional climate warms…

As you’d expect, all basins experienced some degree of snowpack loss under both warming scenarios. But 4 degrees Celsius of warming proved far more detrimental than 2 degrees Celsius of warming…

In the case of the Columbia River Basin, the study’s three-pronged approach — examining current dependence, projected snowpack losses and how much water each basin would need to make up for that lost snowpack — is revealing.

While the Columbia scored better than the San Joaquin and Colorado River Basins in terms of the amount of snowpack it’s expected to lose, the basin’s reliance on snowpack and its need to find new sources of water makes it far more vulnerable than it might at first appear.

Abatzoglou says it’s unlikely the basin can build enough new storage to make up for the natural storage snow provides. But, he stresses, storage is only part of the story. To fully understand the study’s conclusions, you need to look at timing…

For most of the 20th century and into the early years of this century, lack of precipitation during the growing season didn’t present a problem for farming because farmers could irrigate with water from snow that reliably melted during the growing season and reliably accumulated during the off season. But warming temperatures mean not only less snowpack, but also a change in the seasonal timing of that water, which adversely affects irrigation.

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