A River-Running Season Abbreviated

Floating the Yampa River in Dinosaur National Monument. Photo by Brian Richter

____________________

Every January, my email inbox swells with messages from a community of friends — our “river tribe” — that enjoys floating rivers together each summer. We begin organizing ourselves each January to decide which rivers we want to float by raft or kayak come summertime, and to coordinate the dates for which we’ll each apply for river permits.

Our email exchanges were particularly animated this January because the news media were reporting a heavy snowpack and excellent skiing across the Rockies, Sawtooths, and Cascade mountain ranges. To us this translated into a promise of abundant snowmelt runoff for river-running in the spring and summer in the Colorado, Green, Yampa, San Juan, Chama, Salmon, Snake, and Rogue rivers. We would have lots of great choices this year!

November 2019 was very kind to the Colorado River basin, with some areas experiencing precipitation that was more than 500% of average. The Rocky Mountain headwaters received 110-200% of average snowfall in November that was substantially augmented by additional snow in December.

Week by week, our river tribe carefully watched the runoff forecasts being generated by agencies such NOAA’s Colorado Basin River Forecast Center. A key function of the CBRFC is to forecast how much water will be produced in the Colorado River from the Rocky Mountain snowpack during April-July. Their first forecast, on December 16th, projected snowmelt runoff to be a bit less than average (83%), the consequence of a very hot and dry fall of 2019 that had parched soils in the upper basin. The CBRFC hydrologists knew that once the snowpack would begin to melt in spring, soil moisture would need to be recharged before runoff could begin in earnest; hence, even though the snowpack was above normal, the soil moisture deficit lowered the initial runoff projection below average levels.

A hot and dry fall of 2019 sucked the moisture out of soils in the Upper Colorado River basin. Many areas would require more than a foot of snowmelt water to refill the soil moisture deficit before runoff could begin in spring of 2020. This soil moisture deficit caused the CBRFC to forecast a less-than-average runoff for the spring & summer of 2020, even when snowpack levels were above average at the beginning of the year.

But even while accounting for the soil moisture deficit, the runoff forecast for the Upper Colorado River was still looking pretty good, holding steady and reasonably high, even improving to 87% of average by mid-February. We dreamed of splashing through whitewater in Echo Park on the Yampa River, in Lodore, Desolation, and Gray Canyons of the Green River, or in Westwater and Cataract Canyons of the Colorado River.

But then the forecast starting turning south and looking bad! January and February brought little snow, followed by a horribly dry April and May. The CBRFC runoff forecast fell precipitously, looking as dismal as the rapidly plummeting Dow Jones index in late spring.

The runoff forecast for the Upper Colorado River basin began dropping in March, and then plummeted rapidly in late spring, finally ending up at 50% of average. Data from NOAA’s Colorado Basin Runoff Forecast Center.

The meager snowfall in late spring certainly explains a lot about the precipitous drop in the runoff forecast, but I wondered whether something more had driven the unexpectedly steep decline. I had a delightfully informative chat with Paul Miller of the CBRFC (BTW, Paul is one of the friendliest and most helpful scientists I’ve ever spoken with). Paul explained that the forecast model is based upon long records of temperature and precipitation — particularly those measured during the early spring months — and the eventual snowmelt runoff that is expected to come in April-July. However, as Eric Kuhn stated recently on the Science Moab radio show, “Climate change is totally disrupting those basic assumptions.”

What Eric means is that statistical runoff forecasting built on a long history of observations is now becoming increasingly inaccurate as the climate warms and changes those relationships. With a warmer climate, more of the snowpack is now evaporating directly (called sublimation) and not producing any runoff, and the snow that does melt is melting faster than it has in the past. This explains why climate scientists are predicting progressively lower and earlier runoff in basins like the Colorado in coming decades as the climate warms.

Paul Miller says that because the CBRFC forecast model utilizes only 10 days of forecasted temperatures and then relies on historical temperature values, his group is needing to pay closer attention to melting snowpack levels and make more frequent adjustments to its forecasts to account for the rapidity with which snowpack levels are now declining in the spring, especially in years like this one that are very dry and warm. Paul says the agency is constantly working to improve forecast models to reflect these changing temperature impacts.

The end result for river-runners this year was a much lower and much shorter season than what we were expecting at the start of the year. We should expect more of these surprises in the future as the climate warms.

A shorter river-running season does not bode well for my river tribe. Already, the annual competition to obtain limited river permits on Western rivers is fierce, and our tribe has been unable to draw any permits for any rivers in recent years. With a shortening runoff season that competition is certain to intensify, as river runs in the later summer months will soon become impossible.

Maybe it’s time to take up a new dryland sport?!