The Colorado River Basin provides freshwater to more than 40 million people within the semi-arid southwestern United States, including major cities such as Las Vegas and Los Angeles. However, between 2000 and 2021 the basin experienced a megadrought (a severe drought lasting multiple decades), which researchers have suggested likely would not have occurred if it were not for anthropogenic climate change. In particular, during 2020 and 2021, the river basin recorded the driest 20-month period since 1895 and the lowest river flow since 1906.