On the cover

An atmospheric river—a long, flowing band of concentrated water vapor—formed an arc on 20 February 2017 that stretched from Hawaii to the western coast of the US. The system delivered record-breaking daily rainfall to parts of California during an already wet year, and it caused floods, landslides, and debris flows. See the Quick Study by Serena R. Scholz and Juan M. Lora to learn about the formation of atmospheric rivers and their global impacts under a changing climate. (Image by Jesse Allen, NASA Earth Observatory, using Suomi NPP VIIRS data; compass rose adapted from iStock.com/Anton Porkin.)