Rain falling on Southern California is expected to aid firefighters mopping up multiple wildfires. But potentially heavy downpours on charred hillsides could bring new troubles such as toxic ash runoff.

Rain was falling across Southern California on Sunday, bringing some relief to thousands of firefighters battling multiple major blazes for nearly a month in the Los Angeles area, but also prompting new threats of floods and mudslides across burn-scarred lands.

More rain fell Monday on parts of Southern California after causing mudflows over the weekend, helping firefighters but boosting the risk of toxic ash runoff in areas scorched by Los Angeles-area wildfires.

Rain on the way to parched Southern California on Saturday will aid firefighters mopping up multiple wildfires. But heavy downpours on charred hillsides could bring the threat of new troubles like toxic ash runoff.