In 2020, renewables became the second-largest source of electricity generation in the United States after natural gas (US EIA, 2021). In recent years, wind energy generation has overtaken hydropower as the dominant source of renewable generation in the United States, but hydropower continues to offer advantages, in particular large-scale storage, that makes it particularly valuable as a complement to other weather-driven renewables. This storage, in the form of reservoirs, is rarely managed exclusively to optimize hydropower generation. Instead, reservoirs are operated for flood control, ecosystem services, irrigation, water supply, navigation, and recreation as well as hydropower. Managing these competing demands in a changing climate with existing infrastructure creates difficult challenges, because all these demands are themselves subject to change as is the electricity demand itself. Yet many climate change impact studies continue to treat rivers as entirely natural systems and water resources infrastructure is ignored or treated as an afterthought. In this presentation, we will discuss recent climate change impact studies in both the northwestern and southeastern United States in which we quantified the effects of regulation on discharge and other variables. We will make the case that to develop new strategies for mitigating and adapting to climate change, it is paramount to account for humans as active agents in the hydrologic cycle. The first study focuses on the Columbia River Basin in the Pacific Northwest, the main hydropower producing region in the United States, and examines the effect of accounting for regulation on changes in high and low flow extremes. The second study focuses on the southeastern United States and evaluates the effects of regulation on estimated changes in flow, stream temperature, and habitat suitability. US EIA, 2021: Monthly Energy Review, July 2021. www.eia.gov/mer [Last accessed on 8/3/2021].