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Another wacky ‘Water Year’ in the books

For Denver Water, the official water year of 2021 brought another round of plot twists.

Water Year 2021 had its share of surprises, some of them even happy ones.

Climate specialists and water watchers track precipitation patterns over a period spanning Oct. 1 through Sept. 30, the “water year” that annually resets about the time snow begins hitting the highest peaks.

No water year is the same, of course, but as the influence of climate change has stirred up what used to be more established patterns, the year-to-year variability keeps scientists and water managers less and less sure about what each year might bring. 

A big monsoon season kept water levels high at Dillon Reservoir into August. It was a break from recent summers, when monsoon rains have been disappointing. Photo credit: Denver Water.

At Denver Water, the 2021 water year sprinkled some good news at different times at various spots within the utility’s 4,000-square-mile water collection system.

Front Range precipitation in late winter, spring and early summer kept water demands low in Denver Water’s service area, easing pressure on reservoirs. 

That wet weather included the big mid-March snowstorm (the “Pi Day” storm as some named it), officially the fourth largest ever, with a snow depth of 27.1 inches at Denver International Airport.

That storm, along with big rains that came in the spring, filled agricultural reservoirs on the Eastern Plains and along the South Platte River corridor. That moisture gave farmers a leg up and reduced the need for them to call for additional water, thus preserving supplies in upstream reservoirs. 

A big mid-March snowstorm provided a big boost to Front Range water supplies and eased drought conditions in parts of the state. Photo credit: Denver Water.

The numbers bear it out: water use between January and May represented the lowest usage in that span for Denver Water customers since 1968.

“That precipitation really had an impact on demand which allowed us to fill reservoirs and leave water on the West Slope,” said Nathan Elder, manager of water supply for the utility.

Later, in July, a healthy monsoon season brought big rains to parts of the Western Slope, delivering double the average precipitation at Dillon Reservoir, and helping keep reservoir levels up. It was a return to the kind of monsoon rains that had been missing the last couple of years and can give a lift to water supplies at the very same time summer demand has typically started to pull volumes down.

Those big monsoons also helped in another important way: curbing forest fires. As a result, Colorado got a break from the record-setting wildfires it saw in 2020, giving landscapes, communities and firefighters a much-needed respite. 

Firefighters put out hot spots after a small fire near Gross Reservoir in October. More rain and snow at the right time made for a far calmer wildfire season than the record year of 2020. Photo credit: Denver Water.

On the downside, the summer’s big rains also led to frequent flooding over the year-old burn areas, leaving some river stretches in northern Colorado and on the West Slope choked with debris, sediment and ash.

Statewide, Water Year 2021 brought better news than 2020. 

The spring rains, most of it on the east side, helped give the state its 11th-wettest May in 127 years of record-keeping. And most of the state ended up in less intense drought categories than when the water year began.

But there were plenty of concerning measurements as well, mostly lining up with what has been predicted would be the impacts of a warming climate.

The number of 90-degree days were far above average in areas across the state. In Denver, there were 61, compared to an average of 43 from 1991 through 2020.

Streamflows were far below normal, even with a snowpack that was only mildly below normal. In the Colorado headwaters, for example, where Denver Water accesses half of its supply, streamflows were at 58% of average — well below the April 1 snowpack that notched in at 91% of average.

The state ended the water year still mostly in some category of drought, and September was the third-warmest statewide, unfortunately stoking a pattern of sorts. 

Read about the many ways Denver Water encourages water efficiency to conserve our water supply.  

“The last seven years, September, the last month of the water year, has been hotter and dryer than normal,” Elder said.

With Water Year 2021 in the books, Denver Water and climatologists are already watching to see what 2022 has in store. 

Denver Water’s 4,000-square-mile collection system spans the Continental Divide. Image credit: Denver Water. 

So far, things look good in the high country, with solid fall snows. 

On the plains, it’s been drier. 

Denver this fall has challenged and toppled a series of decadeslong records for snowless streaks, on Nov. 19 breaking the 211-day mark set in 1977 and 1992. Forecasters expected more records to fall in coming days. 

So keep watching the weather and tune in next fall to see how it all turned out.