River Watch studies climate changes around White River

RBC | Meeker’s former physician and high school science instructor, Dr. Bob Dorsett, has analyzed recent critical temperature and precipitation data on the White River and written a summary report, partially motivated by the algae blooms of the last several years. Dorsett coordinates and implements Meeker’s involvement in the Colorado Parks and Wildlife’s River Watch Program. This summarizes his report.

The data Dorsett analyzed came from weather stations at the river’s headwaters and from gauging stations along the river. The data show a trend of rising temperatures and lower precipitation with earlier peak runoff and lower peak flows. See graph below.

Peak White River flows historically occurred in early June and averaged around 3500 cfs in the early 1950s, with considerable year-to-year variation. The spring runoff these days occurs earlier (60 some days after the spring equinox) than it did in 1950 (70 some days after spring equinox). Now peak flows average roughly 500 cfs lower than they did thirty years ago. In 2015 and 2016, peak flows were well under 3000 cfs.

Earlier peak flows give algae more time to grow in the summer and lead to a longer period of low flow. Decreased peak flow is not as effective at scouring algae off the stream bed, so algae remains on the substrate from one year to the next. Decreased flow probably has other effects on the river ecosystem, as well, including changes in sediment transport and fish habitat.

Since about 2014, the green algae, Cladophora glomerata, has overgrown the river bottom during summer months extending from about the Pot Hole Ranch, below Marvine Creek, down the river to its confluence with the Green River in Utah.

Dorsett’s River Watch work has also documented algae growth in new ponds along the river and in their runoff. The upper reaches of the river have experienced increased development in recent years, with new houses and resorts near the river. Landowners apply fertilizer to hay pastures and recreational grasses along the river, and ranchers continue to pasture cattle along the river, though not as many as in the past. River hydraulics have been modified with partial dams designed to improve fish habitat which modify the river hydraulics, and at least one of the fishing resorts adds substantial amounts of fish food to the river water. The report also documents reductions in runoff that normally scour algae off the stream bottom. Cladophora blooms, Dorsett states, typically result from a combination of factors including nutrient load, increased light, and reduced scouring, among others.

Dorsett concludes that the data show significant trends toward a warmer and drier climate regime at the headwaters of the White River with decreasing flows and earlier spring runoff. They corroborate climate model predictions for hotter, drier conditions in the American southwest and lend credence to concerns over a possible megadrought, Dorsett says. Dorsett hopes this information and his analysis will be of use to water managers for long term planning in the White River drainage.