Water lost to evaporation from lower Snake River reservoirs

This briefing by the Stockholm Environment Institute quantifies the additional water lost to evaporation caused by the four lower Snake River dams compared to a free-flowing river state. The study finds that these reservoirs result in an average annual loss of approximately 30,000 acre-feet of water, which has significant economic and agricultural implications.

• The four lower Snake River dams—Ice Harbor, Lower Monumental, Little Goose, and Lower Granite—cause an average additional water loss of 30,400 acre-feet per year due to evaporation compared to free-flowing conditions between 1990 and 2020.
• Future projections for 2025–2055 indicate that the reservoirs will continue to lose an average of 31,400 additional acre-feet of water per year to evaporation, with estimates across eight global climate models ranging from 30,100 to 32,800 acre-feet/year.
• The annual evaporation loss of roughly 30,000 acre-feet is estimated to be worth approximately $110 million as a water right, based on a 2024 estimated price of $3,680 per acre-foot.
• The volume of water lost to evaporation from the dams could alternatively support the household needs of approximately 240,000 people or be used to grow about 8,000 acres of apples.
• The increased evaporation is attributed to the difference in surface area; the reservoirs have a total surface area of 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} }