Over the past two decades much of western North America experienced persistent drought with little to no respite. Consequences were widespread, including declines in river flow and reservoir storage, over-extraction of ground water, explosion of forest-fire activity, and massive bark beetle outbreaks. Water-balance calculations make clear that 2000–2018 was easily the driest 19-year period in the past century. To what degree if at all is human-caused climate change responsible and what is the future trajectory of water supply in western North America?
