Golden cottonwood trees and shorter days signal not just the changing of the seasons, but also the transition from one water year to the next, as irrigation demands taper off and snow starts to accumulate in the high country. Oct. 1 is the official turning point, so 2015 has already arrived in water time.
The 2014 water year brought relief to most of Colorado and the Upper Colorado River Basin after two very dry years. Above-average precipitation eased drought conditions and allowed reservoir levels to creep upwards.
Blue Mesa Reservoir, Colorado’s largest, is now 71-percent full, in much better shape than at this time last year, when it was just 42-percent full. Near average inflows brought Lake Powell, the “savings account” for the Upper Colorado River Basin to meet downstream obligations, up to 51-percent full. It was just 45-percent full at this time last year. Inflows to Lake Powell in both 2012 and 2013 were less than half of average.
Soil moisture is also looking pretty good, with levels in most of the Upper Colorado Basin above average, although there are some dry spots in the four-corners area of New Mexico and Arizona and in southwestern Wyoming. Soil moisture in the fall is a factor in how much snowmelt reaches streams and reservoirs the following year, as opposed to being sucked into dry ground.
What will the  water year bring? That remains a largely open question, although it does appear that the Southwest will get some relief from persistent drought. The three-month outlook issued by the National Oceanic and Atmospheric Administration (NOAA) in September indicates that conditions are likely to be wetter than average in Arizona, New Mexico, Southern Utah and Southern Colorado. Farther north in Colorado and Utah and in Wyoming, the three-month forecast shows “equal chances” of drier and wetter conditions.
The Bureau of Reclamation forecasts that the “most probable” inflows into Lake Powell in the 2015 water year will be 98 percent of average, while acknowledging that water supply forecasts at this time of year are highly uncertain. Conditions do appear favorable for another high-flow experimental release in November to benefit the Grand Canyon ecosystem by flushing sediment downstream. Total releases from Powell in 2015 are expected to 8.23 million acre feet, up from 7.480 million acre feet in 2014, which was the lowest release since Lake Powell filled in the 1960s.
This is also the time of year when we can start to look at snowpack numbers to get clues about what the coming water year (and ski season!) will bring. However, it’s also impossible to draw any reasonable conclusions from snowpack numbers now, since the total amounts are so small and “percent of normal” can swing wildly overnight.
So, keeping in mind that this is largely a recreational exercise, we do have some early data: Most Colorado river basins have less than half of the average water content in their snowpack for this time of year, except that the Gunnison has 65 percent and the Arkansas Basin has 93 percent. In Utah, the snowpack in the river basins that drain the Wasatch Mountains into the Great Basin have between 400-900 percent of their average water content for this time of year, while levels in Utah’s portion of the Colorado Basin range from 41-83 percent of average. Snowpack numbers for Wyoming are also way below average, and no data is available yet for New Mexico.
Here are two websites that are very useful for keeping track of climate, water supply and streamflow information:
• The Colorado Climate Center and National Integrated Drought Information System page on Upper Colorado River Basin water conditions, at http://climate.colostate.edu/~drought.
• The University of Colorado-based Western Water Assessment’s “Intermountain West Climate Dashboard,” at http://wwa.colorado.edu/climate/dashboard.html.
You can also get information on current conditions and operations at Lake Powell from the US Bureau of Reclamation at http://www.usbr.gov/uc/water/crsp/cs/gcd.html.