Climate change could slash Colorado stream flows, with effects across the US West: report

Future warming could lead to significant reductions in Colorado’s river flows by mid-century — impacting not only the Centennial State but also its neighbors downstream, a sweeping climate report warned on Monday.

Colorado, a “headwaters” state for much of the U.S. West, has seen persistent dry conditions in recent decades, with four of the five most arid years in its 128-year history of records occurring since 2000, according to the state-funded Climate Change in Colorado survey.

Snow-water equivalent levels — the amount of liquid water contained in mountain snowpack — during the 21st century have already plunged by between 3 and 23 percent in the state’s major river basins, in comparison to 1951-2000 averages, per the report.

“Future warming will continue that trend,” lead author Becky Bolinger, a research scientist at Colorado State University, said in a statement. 

“We would need a large overall increase in precipitation to offset the effects of warming there — an outcome that appears unlikely,” added Bolinger, who also serves as Colorado’s assistant state climatologist.

Colorado’s major river basins — the Colorado River, the Rio Grande, the Arkansas River and the Platte River — could endure 5 to 30 percent reductions in both snow-water equivalent and stream flow by 2050, compared to 1977, according to the report.

“The high mountains of Colorado form the headwaters of major rivers and their tributaries that provide water supply for Colorado and over two dozen downstream states and Mexico,” the noted in an executive summary.

All four of the major rivers have what the authors describe ed a “a snowmelt-dominated hydrology,” in which most of their annual streamflow originates as melting seasonal snow.

But by mid-century, dates for seasonal snowpack peaks will likely occur earlier in the spring than they do now, Bolinger noted.

These warming-driven shifts, the authors warned, could also be accelerated by the presence of “dust-on-snow” — when dust blown in dryland agriculture or oil and gas drilling is buried within snowpack and hastens the melting process. 

In addition to exploring the regional ramifications of climate-induced changes to snowpack, the report focused on Colorado’s stark rise in average temperatures — a surge of 2.3 degrees Fahrenheit from 1980 to 2022.

From a seasonal perspective, the most warming has occurred in the fall, with temperatures increasing by about 3.1 degrees Fahrenheit during that window.

“The observed warming trend in Colorado is strongly linked to the overall human influence on climate and recent global warming,” the report authors warned.

“Further and significant warming is expected in all parts of Colorado, in all seasons, over the next several decades,” they added.

Statewide annual temperatures are expected to jump by 2.5 to 5.5 degrees Fahrenheit compared to a 1971-2000 baseline, and by 1 to 4 degrees compared to today, in a medium-low emissions scenario, according to the report. 

Alongside these shifts in temperatures, the authors identified probable expansions in climate hazards and extremes, including increased wildfire incidence, greater and more severe drought occurrence and up to a ten-fold surge in heat wave frequency by mid-century.