Cover image: Pictured is an intake tower of the Hoover Dam on Lake Mead near Las Vegas, Nevada. The largest reservoir in the United States, Lake Mead is now at slightly more than one third its capacity. Since 2000, the water level in the lake has dropped by nearly 40 m. A further drop of less than 3 m would trigger a level 1 water shortage declaration for the first time in the lake’s history, potentially restricting water supply to Nevada and Arizona. See the introductory Perspective by Glen M. MacDonald on pages 21256–21262 for the Climate Change and Water in Southwestern North America Special Feature. Image courtesy of Glen M. MacDonald.