El Niño and global warming are mixing in alarming ways

AFTER YEARS of praying for more rain, Californians unexpectedly found themselves wishing for less this week, when tropical storm Hilary blew in from Mexico on August 21st. Rainfall records were smashed in Los Angeles and San Diego. Death Valley, farther inland, was deluged with as much rain in a day as it normally receives in a year. Inundated roads completely cut off the nearby city of Palm Springs (pictured) for a time.

Hurricanes and tropical storms hit California only very rarely: none had even come close since 1997, and the previous one to make landfall was in 1939. Most of the few that have reached the state, however, including Hilary, have coincided with El Niño, a weather pattern that temporarily raises global temperatures while redistributing heat and moisture around the world.