October 1st Climate and Water Report for Utah
Current Valley Conditions (SCAN)
September brought more typical conditions than the past two months, with 0.7 inches of precipitation accumulating in Utah’s valley locations. Southeastern Utah fared the best during September, receiving 1.4 inches, while Southwestern Utah received a paltry 0.3 inches. Overall, Utah’s SCAN sites ended up the 2021 water year with an average of 8 inches of precipitation. Although below average, this would have been significantly worse if it weren’t for the exceptional monsoonal moisture of July and August. Soil moisture levels dropped through September, as evapotranspiration rates remained high at Utah’s SCAN sites. At the end of the water year at Utah SCAN sites, soil moisture conditions were generally below average, but higher than last year at this time. Soil temperatures across most of the state ended September near or above normal. Utah continues to persist in severe (D2) to exceptional (D4) drought conditions. Luckily, however, the portion of Utah experiencing D4 drought has dropped to 20%, down from 65% just three months ago.
Current Mountain Conditions (SNOTEL)
With September in our rear view mirror, we now can bid adieu to the 2021 water year. Good riddance! The 2021 water year precipitation ended at 82% of average for Utah’s mountains, up from 64% earlier in the summer. Accumulated precipitation hovered at or below the previous record minimum for much of the water year until our recent boost from the summer monsoon, which pushed totals to just above the bottom 10th percentile of observations. If we combine the statewide precipitation deficit from the end of this water year with last year’s, we get roughly 13” of additional moisture (above and beyond what we normally receive) that will be needed to get us back to ‘normal’. For context, the average annual statewide precipitation is 32.1”, so our current deficit is roughly 40% of what Utah normally gets in a year. Reservoir storage ended the water year at 48% of capacity, down 15% from last year and down 26% from the previous year at this time. Fifty percent of Utah’s rivers are in the driest categories for streamflow for this time of year, and Water Availability Indices (WAIs) remain at historically-low levels (bottom 15th percentile) for 10 of Utah’s 18 major basins.
And yet, there’s hope. As noted in last month’s report, the unusually strong summer monsoon provided much-needed improvement in the amount of soil moisture available in Utah’s mountains. While things have dried out somewhat since then, statewide soil moisture is currently at 36% of saturation, which is close to average for this time of year and up 13% from last year’s value. Soils are likely to remain at around average moisture levels or above because we are now entering the fall season when our mountain soils don’t lose as much moisture to evapotranspiration compared with summer months, and certainly any additional precipitation we receive before the snow season will help. All of this will lead to an improved amount of runoff during next spring’s snowmelt season, which ought to help replenish our reservoir system. Assuming we get a reasonable amount of snow…
Finally, please note that starting this water year the National Water and Climate Center (NWCC) has migrated to the new 1991-2020 climatological normals window. In addition, all NWCC normals will use median instead of average as the measure of central tendency. The Utah Snow Survey office will be publishing a special report in Fall 2021 to explain these differences and their potential impacts on our understanding of current water supply conditions. Please contact us with any questions or concerns in the meantime.