Monsoon storms have brought welcome moisture to southwest Colorado this summer, improving surface soil conditions after a dry spring.
But beneath the greener landscape, the region’s larger water deficit remains.
National Weather Service hydrologist Erin Walter says the monsoon arrived later than usual this year, with moisture increasing substantially in July after several dry months and a record-low snowpack.
The rain has improved some measures of drought. It has not improved all of them.
“When we're talking about drought or trying to measure drought, the meteorological conditions are just one component,” Walter said.
Meteorological drought measures shortages in rain and snow. Other indicators include streamflow, agricultural impacts, vegetation health and longer-term water supplies.
Walter said estimates showed the upper 10 centimeters of soil nearly saturated in many areas near the Four Corners following the storms. But moisture roughly a meter underground remained below saturation.
Streams have also continued to reflect the longer-term deficit.
Walter said streamflow across the region remained below average in many cases, with some gauges at or near record-low levels for the time of year.
That difference helps explain how summer storms can noticeably change conditions on the ground without repairing the region’s overall water supply.
Monsoon rain is no substitute for snowmelt
Reservoirs in southwest Colorado depend heavily on mountain snowpack and the spring runoff it produces.
“The monsoon rain can help, but we do rely on that snowpack to supply all of our reservoirs,” Walter said. “The amount it contributes is much lower than what we would expect inflow to be during that peak runoff in May.”
Walter cited Bureau of Reclamation figures for McPhee Reservoir. Average inflow during May can exceed 84,000 acre-feet. Average July inflow is less than 12,000 acre-feet.
By mid-August, Dolores Water Conservancy District General Manager Ken Curtis said McPhee was nearly out of its active storage capacity and approaching its lowest allowed operating level.
“The lake's almost empty of its active capacity,” Curtis said.
Curtis described this year’s water supply as “abysmal.”
Full-service irrigators received about 14 percent of a full supply this season, he said. The Montezuma Valley Irrigation Company was operating at roughly 55 percent.
Curtis said this year ranks among the third- or fourth-worst runoff years on record for the project.
One major factor came before the monsoon ever arrived.
Curtis said exceptionally warm conditions in March accelerated the loss of snow and sharply reduced the runoff that would normally replenish McPhee.
“The heat in March was definitely unprecedented,” Curtis said. “It did yank the legs out of the runoff, making it not the worst year, but down near the bottom.”
Then came a monsoon that, from the perspective of reservoir and irrigation supply, has not been enough to make up the difference.
Curtis said rain in July provided some temporary help to the Montezuma Valley Irrigation Company, but the wetter pattern lasted only about a week before tapering off.
“The monsoons so far have underperformed,” he said. “There’s still time. The monsoons run through September, so we’ll see.”
Farmers bear the shortages
McPhee is expected to continue dropping as the irrigation season winds down.
Curtis said the reservoir was about six feet above its lowest allowed stage at the time of the Aug. 13 interview and expected to reach that level near the end of the month.
Municipal water supplies are protected and will continue operating throughout the year, he said.
Agricultural users have borne the brunt of the shortage.
Curtis said fields served by senior water rights in the Montezuma Valley remain greener, while many fields farther north toward Pleasant View have been left fallow.
More rain through the end of summer would still be useful.
Fall moisture can improve soil conditions and help prepare the watershed for winter. It can also benefit the natural landscape after months of heat and dryness.
But Curtis said the region is already looking toward next year.
Attention turns to winter snow
The Climate Prediction Center outlook cited by Walter favored wetter-than-normal conditions in southwest Colorado through the remainder of summer and into fall. The outlook gives the region roughly a 30 to 40 percent chance of above-normal precipitation, with the August-through-October period also leaning wetter.
That could provide additional relief for soils and vegetation.
It would not eliminate the need for a strong winter.
“We're totally at the mercy of winter snowpack,” Curtis said. “A little bit of fall rains would help start that, but we will anxiously watch the snowpack.”
McPhee will enter that winter with little stored water available to cushion another poor runoff year.
Curtis said anything less than a more typical winter could mean another year of shortages.
A single good winter can produce a full water supply, he said.
After one of the region’s poorest runoff years on record, that is now the weather event southwest Colorado’s water managers are waiting for.
