August 1st Climate and Water Report for Utah
Current Valley Conditions (SCAN)
July brought some welcome relief to Utah’s Valley locations, where more precipitation fell than in the previous three months combined! An average of 1.6 inches was recorded at Utah’s SCAN sites in July, bringing the water year total to 5.8 inches. Southern Utah fared the best this month, which is fortunate since it is the region in greatest need of precipitation. Soil temperatures across most of the state moderated during the month, ending July near normal. Thankfully, this significant change in the weather has produced small but meaningful improvements in the drought situation in Utah: although 99% of the state remains in Extreme (D3) to Exceptional (D4) drought, the portion of Utah experiencing D4 is down to 51%, from 64% at the beginning of the month.
Current Mountain Conditions (SNOTEL)
Monsoon! While we are still deep in drought, this summer’s unusually strong monsoonal precipitation has helped boost the water supply conditions in Utah’s mountains. July’s accumulated precipitation was 186% of normal and improved the statewide precipitation total at Utah’s SNOTEL sites by 2.5 inches. Whereas we started July at 9.6” below average, by the end of the month this number was down to 8.5”, and additional monsoonal moisture in August has brought that value down a bit more. In addition to improving our precipitation totals and soil moisture levels (more on that below), the strong monsoonal moisture has also helped in several ways, including: (a) a reduction in the rate of water withdrawal from our reservoir system (because less water is needed for irrigation and landscaping when it’s being delivered as rainfall), (b) decreased fire risk, and (c) an improved likelihood of an efficient snowmelt runoff when next winter’s snowpack melts in spring 2022. This is because soil moisture levels tend not to vary during winter months in Utah’s mountains, so whatever amount of soil moisture is available in headwater soils going into the snow season tends to be intact when the snowmelt begins. Last year’s phenomenally dry soils were a major reason why we ended up experiencing the severe drought conditions that are ongoing. If we can enter this coming winter’s snow season with wetter soils, that will improve the chances for an average or above-average runoff, depending on how much snow we get… This last point (c) is the most important benefit the monsoonal moisture has provided from a water supply perspective.
That said, Utah’s water supply conditions are still in very poor shape. Our water-year-to-date accumulated precipitation is 70% of average and is in the bottom 10th percentile of the historical observations . To help create a picture of how much moisture Utah would need to get out of the current drought, we need to combine the current precipitation deficit relative to normal with last year’s; this gives a value of roughly 16.2” of precipitation. Certainly this isn’t a perfect measure of what the state needs to no longer be in a drought situation—for example, the shortages in our reservoir system are not accounted for—but at least this gives a rough picture of how much additional moisture is needed to get us back to ‘normal’. To be sure, that’s around 16” of additional precipitation, meaning that we need that much more rain and snow than we would normally receive.
Statewide soil moisture benefited significantly from the recent rainfall—currently at 44% of saturation, up 6% from last month. Soils in central and southern Utah and the Tooele area fared the best from the monsoonal precipitation with basins above 150% of normal for this time of year. Last winter Utah’s soils reached historically dry conditions and have been hovering near or below record lows until this recent influx of moisture. As noted above, we will keep fingers crossed that we can sustain reasonably moist soils going into our snowpack season.
Utah’s reservoir storage is currently at 52% of capacity, which is 24% lower than last year at this time. While the state’s overall storage has declined, the rate of decline has slowed due to the recent rain and other factors. As noted in last month’s report, Utah’s reservoirs are very unlikely to see substantial gains until next spring’s runoff. April to July streamflow in Utah has been incredibly poor: roughly half of the gage locations in the state reported flow volumes only 25% of normal or lower, and 16 hit new record lows. These ongoing water supply conditions are causing Utah’s current Water Availability Indices (WAIs) to remain at historically-low levels (bottom 20th percentile) for 14 of Utah’s 18 major basins.