LOS ANGELES | Fri May 15, 2015 6:04pm BST

A rare May storm has brought much-needed rain to drought-parched Southern California, but Los Angeles Mayor Eric Garcetti on Friday urged residents of the second-largest U.S. city not to slack off on water conservation.

A storm originating in the Gulf of Alaska brought a wave of showers across Central and Southern California beginning on Thursday afternoon, delivering up to half an inch (1.3 cm) of rain to parts of the state.

The National Weather Service has called those rainfall totals impressive for late spring in Southern California, a region struggling into its fourth year of a devastating drought that has prompted strict water conservation measures across the state.

"Every little bit of rain helps, but our drought emergency remains critical," Los Angeles Mayor Eric Garcetti said in a statement as a light rain fell across the city.

"Angelenos must continue aggressive conservation efforts, and in the wake of this storm, sprinklers should be turned off for at least a week," Garcetti said.

The mayor also reminded residents that Los Angeles was offering rebates to install so-called smart sprinklers that adjust to changing weather and to adopt low-water landscaping.

California's drought has prompted Governor Jerry Brown to impose the state's first-ever mandatory cutbacks in urban water use, up to 36 percent in some communities.