Hydrology and Big River Update
From wet to dry – whiplash to continue in 2024?
After a wet and joyous 2023 water year, water managers and planners are feeling a little less optimistic about 2024. The good times from the previous period of plenty are now replaced with a feeling of foreboding, like the morning after a great party, as we face a below average forecast for 2024.
Locally, there is good news to lessen the potential whiplash. Water supply conditions remain good with average to above average soil moisture conditions and healthy carryover storage projected for most of the reservoirs in the District. Also potentially hedging against a dry 2024, is the return of a strong El Niño, with near record warming of sea surface temperatures in the eastern Pacific. This is generally correlated with increased precipitation in the southwestern U.S, especially in the spring. According to NOAA Climate Prediction Center, “El Niño remains the major climate driver and is expected to be the primary influence on the mid-latitude circulation” for the near term. Figure 1 reflects this with a slightly wetter near-term (Jan-March 2024) outlook.
Unfortunately, the benefits of El Niño circulation patterns may be adversely influenced by the significant warming that is affecting the region and across the globe. Climate scientists have now confirmed that 2023 was officially the warmest year ever for the planet.
Regional Water Supply Forecasts and Projected 2024 Operations:
Across the Upper Basin and for inflows to Lakes Powell and Mead, the early water supply forecasts are not good and represent a significant departure from the heady days of 2023; the days of increasing or even stable reservoir levels may not persist into the near-term picture, without some changes.
Since the last staff hydrology memo presented in October 2023, the once near-average seasonal inflow forecast volume for April to July of 2024 has decreased precipitously, losing more than 3 million acre-feet (“maf”), according to the Colorado Basin River Forecast Center, due to excessively dry conditions. The current unregulated inflow forecast for Lake Powell is 4.80 maf or 75% of average and the unregulated inflow forecast for the entire water year for Lake Powell is 7.62 maf or 79% of average. Combined with a projected 7.48 MAF release from Glen Canyon dam, pursuant to the 2007 Interim guidelines, and consideration evaporation losses, annual inflow could be almost the same as annual outflow putting Lake Powell projected elevations to be unchanged at approximately the same elevation of 3668.5 feet AMSL at this same time next year, under this most probable (50% exceedance) inflow projection.
For Lake Mead, the most probable projection indicates that Level 1 shortages will likely persist in the Lower Basin in 2024, with Hoover Dam releases limited to about 8.4 million acre-feet to meet reduced downstream demands.