Gunnison County reaches exceptional drought as Tomichi Creek thins

Half of Gunnison County is now in exceptional drought, the most severe category the U.S.¹ Drought Monitor uses. In the week of September 8 the share of the county rated exceptional jumped from about 22 percent to just over 50 percent.¹ The other half of the county is in extreme drought.¹ For the first time this year, none of the county is rated any better than extreme.¹

The severity had been flat for most of the summer.¹ From mid-August through the end of the month, about 80 percent of the county sat in extreme drought or worse and about 22 percent in exceptional.¹ The first week of September pushed the extreme-or-worse figure to 91 percent.¹ The second week took it to 100 and more than doubled the exceptional share.¹ Two weeks did what the previous two months had not.

The Drought Monitor's own description of the exceptional category is exceptional and widespread crop and pasture losses, with shortages of water in reservoirs, streams and wells creating water emergencies. Statewide this season, 64 percent of Colorado's pasture and rangeland is rated in poor or very poor condition, against a five-year average of 23 percent. That is a statewide number, not a Gunnison Basin one, but the basin's hay meadows and upland sagebrush are inside it.

The shortfall starts high above the basin. The Butte snow station, at 10,190 feet about 24 miles from Gunnison, has recorded 18.6 inches of precipitation since the water year began last October, 74 percent of its median for the date.² Cochetopa Pass, at 10,020 feet about 32 miles out, has recorded 11.7 inches, 70 percent of median.² Those are precipitation totals, not snow on the ground; both stations are bare in September as they always are. Tomichi Creek runs on that mountain water. It peaks in late May or early June and recedes through the summer, with several small irrigation diversions drawing from it along the way. The gauge on Tomichi Creek at Gunnison read about 20 cubic feet per second this week, on a creek that still has a month or more of recession ahead of it before winter.³

Brown trout are the fish most exposed to a thin September flow in this reach. They spawn in fall, from September into December, once the water cools into roughly the 41 to 54 degree range, and they need enough depth and current to reach clean gravel and keep a nest of eggs watered and silt-free through the winter. A creek reduced to shallow riffles and separated pools blocks that movement and leaves whatever gravel is used at risk of drying out. Water near the Gunnison gauges was running around 54 degrees this week, which is comfortable for trout.³ The trouble with a small volume of water is not that it is warm now; it is that it heats and cools faster across a day and loses its buffer against low oxygen. The case-building caddisflies logged along these streams through August do the coarse work of shredding the leaves that are beginning to fall into the channel now, and they need cool, continuously moving water over gravel to do it.

Satellite passes this week show no cluster of fire detections within 30 miles of Gunnison, only a single weak nighttime pixel near Crested Butte that could be almost anything.⁴ The sagebrush is going into dormancy dry, with grasses and forbs beneath it cured, and that is the fuel that carries fire through sagebrush country. The next Drought Monitor map comes out September 18.