Hand-wave. Numbers and sources please or I won't bother with you again. What I'm talking about can be found in any grade-school science page.
Much of the rain that falls in dry areas evaporates before it hits the ground (you can see it). If it does make wet surfaces much of that evaporates after the shower, or is transpired from vegetation. That fraction does not run off or sink to the water table; it rises back into the atmosphere to form clouds to be carried farther and redeposited. So to presume that when rain falls inland, all the water that fell must have come from the ocean is totally erroneous. A substantial fraction has cycled across the landscape (varying with both topography and vegetation).
Frankly, I see the effects cited in the report as a good thing, an effect that could help us transform much of the Great Basin back into a productive savannah instead of the sagebrush wasteland it is today. Without dams and irrigation, that region would be the borderline desert it was before those farms were developed (albeit with heavily subsidized water delivery).
This whole fight over water in the southern San Joaquin Valley is in reality a set of competing real estate scams. I don't like any of the big players involved; they're all government whores. The California Aqueduct moves more water in late summer than the flow of the San Joaquin River would have been without the dams. The bulk of that water evaporates. It's a lot. Don't get me started about soils, vegetation, aboriginal burning, trace mineral composition and albedo when it comes to retaining water in topsoil. Those soils are LONG gone. We don't have that system any more.