At yesterday’s monthly Colorado Basin River Forecast Center briefing, Greg Smith noted, by way of analogy, the winter of 1976-77. Smith explained that he wasn’t forecasting – the fact that the evolution of this year’s forecast is similar to 1976-77 doesn’t mean that the rest of this year will be like that year, or that this year’s runoff will be like 1976-77. But picking analog years is a great communication tool, to give us a sense of what actually happened, historically, in conditions similar to those we might see today.
So let’s look at 1976-77.
- Naturalized inflow from the Upper Colorado River Basin at Lee Ferry was 5.4 million acre feet, the lowest in the USBR’s Natural Flow Database (which goes back to 1906)
- Lake Powell dropped 3.4 million acre feet, the fourth largest one-year drop since Glen Canyon Dam was built (1990, 2002, and 2013 had bigger drops)
- I graduated from high school
None of these are encouraging analogs.