Hydropower accounts for 71% of renewable electrical generation worldwide, and installed capacity may more than double by 2050. Major hydroelectric projects involve construction of reservoirs to buffer the periodicity of river discharge, meaning hydropower typically does not suffer from supply intermittency of other renewables such as wind and solar. Meanwhile, average greenhouse gas emissions are likely substantially lower than fossil fuel alternatives per unit energy produced. Domestic hydropower production in the United States is unlikely to increase substantially in the foreseeable future, but imports from Canada play an increasingly important role in achieving renewable energy targets in northern U.S. markets...