Has the Upper Snake River System Recovered from Low Water Inventories?

By Matt Harrod:

Don’t count your snowpack chickens yet...

Drought conditions in any drainage/river system used for irrigation results in low water inventories in reservoirs and reduced water availability for irrigation. The Upper Snake River system has had two consecutive years of drought in 2021 and 2022 which has depleted stored water and resulted in curtailments in surface water available for irrigation. The 2022/2023 water year beginning last October has brought above average snowfall in the mountains and has promise to end the drought and low water inventories of the last two years. When will we know for certain when we are out of the drought cycle?

The chart below shows the rate of recovery in daily water inventories after a drought in the previous year. Roughly speaking, inventories in those years recovered at a very linear and uniform rate and then split into two distinct groups beginning in late April and early May. Years in which water inventories peaked at that time were followed by summers with continued drought and reduced water available for irrigation. Years in which inventories continued to climb into June were followed by summers with ample water availability.

In other words, although 2023 snow pack in the upper Snake River system in trending above normal, we won’t know for sure what the 2023 irrigation water availability will be until mid to late May. Note that the determining swing (up or down) could happen as soon as early April (88/89) or might not happen until late May (07/08). Determining factors include late season snowfall, rate of melt-off (not too fast), rainfall on the snowpack (melt-off is too fast), dry soil in the mountains soaking up moisture, and, obviously, spring rains. A 2023 recovery looks promising thus far, but we likely won’t know for sure for another one or two months.