Colorado’s spring runoff is expected to take a hit as the impacts of last year’s drought linger.
A forecast published this week by the National Oceanic and Atmospheric Administration calls for much-below-average — 50 percent to 70 percent — to below-average — 70 percent to 90 percent — spring runoff across most basins in Colorado. Several points in north-central Colorado and in the Arkansas Basin could fare better, with predictions of near-average or 90 percent to 110 percent of runoff.
“What we’re seeing is a lot better than what we observed last year,” said Greg Smith, a senior hydrologist with NOAA’s Colorado Basin River Forecast Center. “We have a long way to go, though, because we have a moisture deficit from last year to make up for.”
Last year’s drought, the second worst in 124 years, parched soils across the state. Before entering rivers and streams, snow and runoff first must satiate a very thirsty ground.
“You see a spring pulse that is not as big and that comes earlier,” said Jeff Lukas, a research integration specialist for Colorado and Wyoming for the Western Water Assessment.
Farmers using diversion systems to irrigate and wildlife and fish that need stream depth for spawning and shelter are primarily hurt by smaller and earlier runoff, Lukas said.
Municipal water suppliers tend not to feel the impacts of low runoff as immediately because of the storage capacity of reservoirs, Lukas said.
Colorado Springs Utilities’ systemwide storage, for example, is at 75 percent capacity compared with last year’s 84 percent and the 1981 to 2010 average of 72 percent, according to data presented at Wednesday’s Utilities board meeting. Furthermore, systemwide storage levels are expected to remain fairly steady over the next couple of months.
“A low spring runoff due to the existing low soil moisture conditions has the potential to impact Colorado Springs’ yield this summer,” said Kalsoum Abbasi, Utilities’ water conveyance supervisor. “While it can reduce the amount of water that physically makes it to our reservoirs, most of our mountain reservoirs are located right next to their collection sites so this direct impact tends to be minor for Colorado Springs.”
Abbasi continued, “The biggest impact is usually that our storage season is shorter, because if senior water rights holders run short of water early they are forced to place river calls earlier than usual, which means Colorado Springs is not allowed to store water even if we have it.”
Utilities’ Water Conveyance team estimates its summer yield in February using snowpack data and NOAA’s runoff forecasts. Because of a wet 2017, runoffs in 2018 were less affected by soil moisture deficits, but were dragged down by the sheer lack of snow. At this time last year, statewide snowpack was at about 50 percent of normal and only 0.59 percent of the state was not in drought.
NOAA forecasters expected below-average or much-below-average runoff for nearly all forecast points in Colorado, with many areas expected to see less than 50 percent. Snowpack continued to deteriorate into the spring, leading to the fifth-worst runoff season since 1964 in the Upper Colorado River Basin.