Great Salt Lake basin still needs 166% of normal precipitation to get out of this drought.

Preliminary research outcomes:

UCC is focusing on GRACE-FO total water storage (TWS) (includes surface, sub-surface, and groundwater) satellite data from NASA as a new tool to estimate the drought severity and water storage deficit over the Great Salt Lake (GSL) basin during the last two decades (2002 onwards). TWS anomaly (positive and negative) aligned perfectly with drought indices (SPEI, PDSI, scPDSI) and precipitation anomalies. During the past drought periods (2002-05, 2012-16,2018-19, 2020-present), all three types of droughts (meteorological, agricultural, hydrological) coincided with each other and led to a socio-economic and ecological drought. A significant amount of water storage deficit (derived from GRACE-FO data) has been observed during the drought periods (2002-05, 2012-16,2018-19, 2020-present) (Figure 1) along with increased evapotranspiration and air temperature than normal. Groundwater level (mean well depth data from USGS) also has a declining trend in recent years like TWS anomaly. Groundwater and natural water availability (estimated from the water budget approach) have shown a 12–15-year lag correlation that indicates a strong relation between initiation or termination of a precipitation drought and the initiation or termination of groundwater drought. Projected frequent droughts in the future will likely increase aquifer vulnerability to droughts as aquifers’ recovery time may be longer.

What historical trend says

During the last two decades, Utah has experienced several high-intensity drought periods along with a low water supply that lasted several months. Although these droughts were not as devastating and impactful as 1895-1907 and 1931-41, the economic and ecological loss due to recent droughts is significant to Utah’s growth. In the last two decades, observed precipitation over the GSL basin was significantly lower than the required precipitation, which caused a water storage deficit. Moreover, population and industrial growth have played a catalyst to disrupt water supply and demand equilibrium. As a result, most of the reservoirs and lakes have been experiencing record low water levels during the last few months. More than 50% of rivers are also experiencing an all-time low or much below streamflow in 2021. Bureau of Reclamation declared a water shortage in the Colorado River for the first time in August 2021. Utah Climate Center also predicted a declining trend of Great Salt Lake level for the next five years.

How the winter might look like

• According to NOAA’s 3-month (DJF) winter outlook, Northern Utah and Southern Utah will have equal chances (below normal/normal/above normal) and below-normal (33-40% chance) precipitation, respectively.

• Seasonal temperature outlook indicates a slightly above normal (33-40% chance) temperature for most of the parts of Utah, and some parts of Southern Utah will have an above-average temperature (42-50% chance).

• The temperature pattern indicates more rain than snow as precipitation which could be a big challenge to the drought recovery.

When can we expect the termination of the ongoing drought?

Preliminary results from the ongoing study estimated a current deficit of ~6.93 inches (176.05 mm) of total water storage over the GSL basin. Assuming northern Utah receives normal winter precipitation (~4.16 inches, i.e., 105.9 mm) (2021-22) in the form of snow, there is a chance of overcoming the recent storage deficit in the next ~12-14 months. If we want to get out of this drought immediately after Spring 2022, we will need at least 166% of normal precipitation during November 2021-April 2022. In the 2016-17 winter GSL Basin had received 154.5% (Figure 2) of its long-term average precipitation from November to April. That strong introduction of the water year pulled the GSL basin out of the drought but unfortunately not for too long. This year we also got a strong start of the water year (started from Oct 01) with a significant amount of snow accumulation in higher elevations and rain in the last couple of weeks which is multiple times higher than the long-term average of October precipitation.

However, there is much debate on getting normal precipitation till mid-2022 in the Western US. There is a strong probability (87%) of emerging La-Nina in the Northern hemisphere and continuing through winter 2021-22, leading to warmer temperatures and enhanced evaporation in the Western US. It could intensify drought conditions in certain places including below-normal precipitation. NOAA's drought outlook indicates persistent drought across the West based on their winter prediction.

Also, the whole recovery process also relies heavily on other factors, e.g., water usage, land-use changes, reservoir operations, and realistic water policy application by the state government.

Scope of future work on Utah water supply

There is much scope to study Utah’s future water supply based on region-specific water budget approach and total water storage variability. Considering more parameters related to water storage will improve the forecast ability in the future. Utah Climate Center aims to forecast water storage deficits based on regional climate variability using machine learning models. This approach will need more extensive and interdisciplinary research work with computer scientists, hydrologists, and the climate scientists at Utah Climate Center.

You can find the latest outlook here published by Utah Climate Center.