The Interior Department declined to make Mr. Goklany available for an interview, and he did not return requests seeking comment.

The misleading language appears in environmental studies and impact statements affecting major watersheds including the Klamath and Upper Deschutes river basins in California and Oregon, which provide critical habitat for spawning salmon and other wildlife. In addition, millions of acres of farms in California’s agriculturally important Central Valley are supplied, in part, by the Klamath, which is California’s second-largest river by volume and is only slightly smaller than the Colorado River. Thirsty farms there have used increasing amounts of water at a rate that scientists say hurts wildlife and imperils the salmon industry.

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Scientists and policy experts say that, by embedding an inaccurate sense of uncertainty about scientific findings in its documents, the Trump administration is advancing its policy of weakening environmental rules and reallocating vast quantities of water to farming and irrigation, even though climate change projections show that use to be unsustainable. Last month, President Trump signed a memo in California relaxing regulations that have limited the flow of water to irrigate the Central Valley’s big farms.

“Highlighting uncertainty is consistent with the biggest attacks on the climate science community,” said Jacquelyn Gill, an associate professor of paleoecology and plant ecology at the University of Maine. “They’re emphasizing discussions of uncertainty to the point where people feel as though we can’t actually make decisions” based on the research.

Mr. Goklany has been employed by the Interior Department since the 1980s, much of that time in less influential positions focused on policy analysis. He has also written papers for and participated in events hosted by libertarian think tanks including the Cato Institute and the Heartland Institute, which have spread doubt about the scientific consensus that human activity is causing the world to warm rapidly. In 2009, he appeared as an expert voice in a film titled “Policy Peril: Why Global Warming Policies are More Dangerous than Global Warming Itself.”