Water lost to evaporation from lower Snake River reservoirs

The four lower Snake River dams cause an average additional water loss of approximately 30,000 acre-feet per year due to evaporation compared to free-flowing conditions. This loss is valued at roughly $110 million as a water right and is equivalent to the water needed to grow 8,000 acres of apples or supply the household needs of 240,000 people. Future projections (2025–2055) suggest these losses will persist or slightly increase, ranging from 30,100 to 32,800 acre-feet per year across eight global climate models.

• Between 1990 and 2020, the four lower Snake River reservoirs lost an average of 30,400 additional acre-feet of water annually to evaporation when compared to predicted free-flowing conditions.
• Future projections for 2025–2055 estimate an average additional loss of 31,400 acre-feet per year, with estimates from eight global climate models ranging between 30,100 and 32,800 acre-feet per year, assuming storage volumes remain consistent with 1990–2020 levels.
• The additional evaporation loss of approximately 30,000 acre-feet per year has a calculated economic value of about $110 million as a water right, based on a 2024 estimated price of $3,680 per acre-foot.
• The volume of water lost to additional evaporation is equivalent to the amount required to support the residential needs of 240,000 people or to irrigate approximately 8,000 acres of apples.
• The increased evaporation is driven by the difference in surface area; the reservoirs cover roughly 25,000 acres, whereas the estimated surface area of the free-flowing river is around 11,000 acres.

APA

Chalmers, D. (2025). Water lost to evaporation from lower Snake River reservoirs. Stockholm Environment Institute. https://www.sei.org/wp-content/uploads/2025/01/water-lost-evaporation-lower-snake-river-reservoirs-1.pdf

Chicago

Chalmers, Doug. Water lost to evaporation from lower Snake River reservoirs. Stockholm Environment Institute, 2025. https://www.sei.org/wp-content/uploads/2025/01/water-lost-evaporation-lower-snake-river-reservoirs-1.pdf.

Wikipedia

{{cite report |last1=Chalmers |first1=Doug |title=Water lost to evaporation from lower Snake River reservoirs |publisher=Stockholm Environment Institute |date=January 2025 |url=https://www.sei.org/wp-content/uploads/2025/01/water-lost-evaporation-lower-snake-river-reservoirs-1.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{chalmers2025water, author = {Chalmers, Doug}, title = {{Water lost to evaporation from lower Snake River reservoirs}}, institution = {Stockholm Environment Institute}, year = {2025}, month = jan, url = {https://www.sei.org/wp-content/uploads/2025/01/water-lost-evaporation-lower-snake-river-reservoirs-1.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }