March 05, 2015

Will Seattle Have Enough Water This Summer?

There has been a lot of discussion of the lack of snow in the Cascades, with  snow melt being an important source of water during the summer and early fall.

Should we worry about our water supply this summer here in Seattle and environs?

The bottom line:  wise management of water by Seattle Public Utilities and increasingly efficient use of water by the regional population will probably allow us to get through the summer without much problem.

Although this year has been warm and relatively snow-free, there has been normal precipitation, generally delivered every few weeks by warm, wet atmospheric river events.

Seattle Public Utilities (SPU) has a a very nice website that summarizes the situation.  From that website, here is the cumulative precipitation for the city's Cedar/Tolt drainages.   The blue line is the long term average and the red line is the current year--we are very near normal.

But the cumulative snowpack is a very different story.  There is only a small amount of water in the snowpack (equivalent to about 2 inches of liquid water) compared to normal (about 30 inches).  We are FAR behind last year (green line).

But Seattle's water managers are a wise lot and they have learned from experience.  There is always a tension between storing water for summer use and the need to keep the water levels low enough to deal with potential flooding situations.    But since it is pretty clear from weather forecasts that flooding is not very probable, and the fact that heavy precipitation periods are rare after late February, SPU has gone into storage mode....allowing the reservoir levels to rise.
In fact, they have allowed the reservoir levels to rise far about normal for this time of the year (see figure). Smart move.

Another big positive is that water consumption is far less recently compared to a decade or so ago, even though Puget Sound population has grown significantly (see plot). Pretty amazing.  That is due mainly to water-conserving toilets and shower heads.  Also more folks are letting their lawns brown a bit in the summer or are planting drought tolerant plants.  Even though last summer (green line) was much warmer than normal, we used less water than the average of 1998-2008. We can be proud of ourselves.

Can we get through the summer without more snow in the mountains?   My colleagues at SPU are confident they can.  And if one does a simple calculation using the above figures (assuming use of 125 million gallons a day and keeping the reservoirs above the gray (low water conditions) area...we could get though September.

But things won't be even close.   We are going to get more precipitation during the remainder of this winter and spring.  For example, the latest model runs indicate another wet, warm system coming in next week.  For example, the 72h total precipitation ending next Thursday at 4 ?M (see below) has several inches of rain over us, water that SPU will save for next summer.

 The fascinating thing about this year is that it is so much like conditions we expect in roughly 2070 under global warming:   warmer, less snowpack, and near-normal precipitation.   If we can get through this summer without much inconvenience it will be a good sign for our ability to adapt to a changing least in terms of drinking water in Seattle.   But it will take wise management of our water storage and usage to ensure this.

   What about eastern Washington?   It looks like the Columbia River/Snake River systems should be in pretty good shape because they drain off of much higher terrain that does have substantial snowpack this year.  More concerns about the Yakima Basin.


  1. Well that's all well and good for Seattle. What about the Eastside of this lovely state? How about the pear trees in Cashmere?

    What about fire? How are my lungs going to feel by mid-July? Even worse, are we going to see another Pateros?

  2. Interesting and good to know. I'm curious how well Eastern Washington is expected to fare?

  3. Okay, so we can get through an average winter expected in 2070 but what if we have an anomalous warm winter in 2071 where temperatures average +4 degrees warmer than whatever is average for 2070.

    Although, Seattle residents and businesses will have ample water this summer what of our native mountain forests and shrubs. What will be the fire impact.

  4. When we speak of Seattle having an ample water supply in 2070, I think perhaps we lose sight of the fact that the rest of the country will not be so fortunate and that there will therefore be a significant in-migration of those seeking moister climes in the intervening 35 years. Which is to say, we speak of the adequate water supply as if our population will remain stable, as it almost certainly will not.

  5. The Olympic Peninsula may be in the worst shape for water this summer.

    - Douglas

  6. I'm curious about the SPU strategy of topping up Tolt reservoir so early. Are they rolling the dice that we wont have any more huge pulses of wet weather? I wonder how much lead time they need to start releasing water? A lot of people live along the Tolt and that river has some serious velocity when it floods.

  7. sldulin,
    Not rolling the dice. Weather prediction is good enough that we can see big events with some skill 5-7 days out. Enough time to start letting water out if needed...cliff

  8. Our snow loss California's gain. Shasta Lake water level (March 4): 990.60 feet elevation. Full lake elevation and dam crest is 1067 feet. A huge recovery.

  9. So, did the northeast "get all of our snow"? Can you guesstimate how much total snow they got, and how much total snow we usually expect to get? Thinking in terms of volume, not X feet deep here or there. I think the lowlands around Boston have like a 2' base now that accumulations add to or melt off. Not much compared to what the ski areas around here expect. But possibly over a larger total area.

  10. Is there any chance you'll move your talk next week to a larger lecture hall and open up more tickets?

  11. Zach...I am really sorry...that is the biggest room in Kane Hall. KPLU does have a waiting list. Will do another talk at some point. They will be taping it..cliff

  12. How are the non-Seattle reservoirs in Puget Sound?

  13. ditto re the Olympic Penninsula being most at risk. Port Townsend's public water system depends entirely on the run off from the Olympic Mountain snow cap. Last weeks report was the snow cap is only 10% of it's "normal" level. It was as low as 3% the week before - when the weather here in town was in the 50's. All we have to do is look to the mountains and we know we're in trouble. There is NO water conversation plan in place because we've never had to deal with a serious water shortage before...which puts us in an even more precarious position. Why is THAT not in the news?

  14. I live a few miles outside of Port Townsend. The Olympic mountains are typically snow covered at this time of year. What do you see for the Olympic Peninsula water availability this year and in the future?

  15. Good article Cliff. I'm impressed with the ability of Seattle and surrounding areas to drive down their water use in recent decades.

    I appreciate Marks comment earlier. The 2070s , because of climate variability, will have years potentially much warmer than this one, and perhaps drier.

    And if the climate in 2070 average the current year it means will be no real reprieve with snow coming back the next year (as it will in 2016, I hope).

    One would assume the cumulative effect of every year being like this year will be much more difficult to adapt to for humans and ecosystems than an isolated year like this one. Also, we currently we have large glaciers throughout the Cascades that will deliver meltwater in September even after this drought. After many decades of 2070's climate many of those glaciers may be gone.

    For these reasons, I suspect this year is a little like, but does not actually demonstrate what the 2070s will be like in terms of the water issues people and land will face.

  16. Our snow loss California's gain. Shasta Lake water level (March 4): 990.60 feet elevation. Full lake elevation and dam crest is 1067 feet. A huge recovery.

    I did the math about a week ago, and at that point California's reservoirs were about one-third fuller than they were a year earlier. You can do it yourself at this link:

    And yes, Shasta (by far the largest CA reservoir) is in especially good shape. A year ago, it was at 57% of its historical average level. Today, it's at 77% of average. Water content in that reservoir is 2.639 million acre feet, vs. 1.941 million acre feet a year ago, an increase of 36%.

    While it has to be noted that reservoir levels are only part of the picture (the others being mountain snow level and moisture content; soil moisture content; and the water situation in the Colorado River watershed that supplies much of California), the recovery of CA's reservoirs in the past year is remarkable -- and unmentioned in the media, which wants to use a "historic" California drought to scare everyone about global warming.

    The "narrative" is that this is the worst California drought for hundreds of years. In fact, the drought, while severe, is not only past its peak but it was never as bad as the 1977 or 1924 droughts, or as several big droughts in the 1800s.

  17. I'm a little to the east, but we're having the same problem over here. Water is always in short supply when you live in the desert, and this winter has been especially sparse as far as snow is concerned. Hopefully we'll pull through with our reservoirs. At least states have gotten more efficient with using their water supplies.


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