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 climate...at 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.