For a couple of years I have been attending/viewing presentations put on by the Central Oregon Geoscience Society (COGS). I am not a geologist, but the talks have been educational and are occasionally about topics of particular interest to me like local hydrology and hydrogeomorphology. On April 27, Kyle Gorman, long time Central Oregon Region Manager for the Oregon Water Resources Department, gave a presentation titled, Water in the Deschutes Basin: 2020 Hindsight – What Happened? (Click on the title to see a replay.) Kyle discussed local hydrology and water use by irrigators. His presentation even had a couple of informative slides I had not seen before. (Check out the “CDA” graph at about minute 40.) It was a good overview of water issues many of us have been tracking for years, and I recommend viewing the replay of his talk, and perhaps joining COGS if you are interested in presentations like this.
I was surprised, however, by Kyle’s dismissal of global warming as a causal factor in current water shortages. Keep reading for comments on that.
It goes without saying that the overwhelming scientific consensus is that global warming (or heating as I like to call it) is already upon us and effecting our weather. In fact, changes are occurring faster and with larger impact than even the most pessimistic models had only recently predicted. Kyle, however, suggested via the use of a variety of charts that changes in local precipitation are cyclical and will likely return to more abundance in the near future. I appreciate his self-acknowledged optimism, but don’t share it.
Scientists looking at tree rings have concluded that the past 100 years was the wettest period in the western US in the past 2,000 years. So, to draw conclusions about the cyclical nature of “normal” weather since Central Oregon has been settled and records have been kept as Kyle did is questionable.
More importantly, I found it troubling that the one graphic he used showing longer term projections of weather in the Pacific NW called for increased precipitation without any explanation of what the graphic really means. These projections call for more rain, but less snow, which is a critical distinction (more on that below). A more recent study concludes that long term weather in our region will actually be much drier. These scientists state that in the future the Columbia River Basin is likely to resemble the dry Tigris/Euphrates Basin.
Let’s hypothesize, however, that we do get more precipitation in the form of rain. This is also bad for us. Our local aquifer can be thought of as having three layers: shallow, middle, and deep. The shallow layer drains quickly and feeds springs high in the Cascades that create rivers like the Deschutes and the Fall, as well as Bridge Creek, which is the source of about 50% of Bend’s drinking water. The deep layer of the aquifer emerges in springs in and around Lake Billy Chinook. The middle layer emerges as springs between the high Cascades and Lake Billy Chinook. The Metolius River is a good example.
Since settlers first arrived, the Upper Deschutes River has had amazingly consistent year round flows due to an abundant snowpack combined with cool spring and mild summer temperatures. Lots of snow combined with favorable temperatures allowed the snow to slowly melt, feeding the shallow aquifer throughout the spring and summer, thereby creating stable river flows. If snow is replaced by rain, or if higher temperatures melt the snow too quickly (as we have been seeing), then the shallow aquifer will not be consistently replenished and flows will resemble what is typically seen in other systems: highest in spring and diminishing through the summer and fall.
That sort of hydrograph will be a significant change and will likely require commensurate changes in water policy.