One thing this winter is good for, beyond early cherry blossoms and giving hope to those folks who plant palm trees, is that it can serve as a laboratory to explore what our warming climate might be like by the mid-21st century.
The Cedar and Tolt watersheds’ February 2015 snowpack was estimated at 8 percent of normal. Three of four Cedar snow monitors are showing zero percent. The snowpack is, says SPU Water Resources Manager and fish biologist Paul Faulds, “exceptionally low.” UW meteorologist and blogger Cliff Mass says it looks a lot like 2070 out there.
Think of it as a preview of things to come; an opportunity for the folks that supply Seattle with water to ponder and plan for the next 25 years and beyond.
Interestingly, the fact that there’s so little snow in the mountains doesn’t bode ill for Seattle's water supply — at least not immediately. We’ve had plenty of rain and you may still shower, shave, drink and flush as normal. With any luck, that will still be true for greater Seattle until perhaps the 2060s, though that is under review as new data comes in.
But the lack of snow is engaging the city’s water managers in a dynamic process of handling our liquid resources 24/7. Work that used to be seasonal is now round the clock as weather conditions are no longer as reliable or predictable. And that’s pushing water managers to consider climate models and potential hazards and challenges if winters similar to this become the norm.
Water isn’t just about water per se, it’s about an entire ecosystem — in Seattle’s case, the city-owned, 90,000-acre Cedar River watershed. (The city also owns a smaller subsidiary system on the South Fork of the Tolt River.) The Cedar is an extraordinary municipal asset — a wholly-owned watershed (well, 99.8 percent owned), the only one of its kind in the U.S.
Pieced together in the years after the Seattle fire of 1889, it is a public and protected source of high quality, unfiltered water for 1.3 million people in the metro area.
This year, the current winter conditions are such that water managers can learn to handle conditions they might encounter in the future. They're thinking not just about water for drinking, but controlling water for power, fish and flood control. It’s a real time climate simulation.
Seattle Public Utilities uses some 38 different climate scenarios to predict where we’re headed. There are all kinds of variables, including differing assumptions, developed by a host of international climate researchers, on how much greenhouse gas will be pumped into the atmosphere.
According to Paul Fleming, manager of Seattle Public Utilities’ Climate Resiliency Group, those scenarios generally suggest we’re headed toward warmer, wet winters with much less snowpack; conditions that the National Climate Assessment and the University of Washington’s Climate Impacts Group suggest will be the norm. This winter, our average temperatures statewide have been 2 to 6 degrees warmer than 1980-2010 averages. By the late 21st century, we could be seeing temperatures 5 degrees or more warmer again, according to models and simulations.
The Climate Impacts Group predicts roughly 40 to 35 percent less spring snowpack by the 2040s, and 56 to 70 percent less by the 2080s. The study says “The dominant form of precipitation in most Washington watersheds will be rainfall by the end of the 21st century.”
On a damp day recently, standing at Chester Morse Lake—the largest repository of water in the watershed—a viewer would see the surrounding mountains bare and green. Normally, the hills would be mantled in white stuff.
The lack of snow is striking to anyone who has been around awhile — at just over 3,000 feet Snoqualmie Pass looks like it needs a good mowing. Longtime Cedar River managers say they don’t remember so little snowpack in the watershed. The concern isn’t a lack of water but the impact of little or no snow.
The snow effectively acts as a kind of free, frozen reservoir, releasing water as spring and summer progress. If precipitation falls as rain instead of snow, it’s only a problem if you don’t have the capacity to store it somewhere. Storms and sudden downpours hold the potential for flooding. Currently, water being stored in the city’s reservoirs is well above average for this time of year.
A shrunken snowpack and an early spring can signal greater fire risk, warns Fleming. If there’s no or little snow, it can extend fire season and dry out the ground, vegetation and forests that are often kept damp even through summer. That could raise risk and intensity in the watershed’s higher altitude old growth forest. There is evidence of a major fire there in the mid-17th century.
Fleming worries lower snowpack could mean the potential for major forest fires on the West — and usually wet — side of the Cascades. They are looking at new data on this now. Fire season in the Cascades could become a year-round issue, as it has in California.
Some climate scenarios predict larger downpours and potential for more floods. The Cedar River managers have to be aware of such things — releasing water when needed, holding it back at other times to prevent downstream flooding. Depending on the volume and time of year, the system could be overwhelmed and places downriver, like the city of Renton where the Cedar River flows into Lake Washington, could suffer. If you fill more of your reservoir capacity with water because precipitation is falling as rain, not snow, you can lose some of your margin for accommodating huge influxes from storms later in the season.
The reservoir at Chester Morse Lake is limited in this regard. A 100-year-old masonry dam at one end still generates hydro power, but when it was built in 1915, says watershed historian Ralph Naess, it caused ground seepage that resulted in a flood that wiped out the town of Moncton. The railroad town was condemned and bought out by the city as a result. The reservoir must be kept lower to prevent future seepage on that scale. Managing the watershed is sometimes a tricky balancing act.