Much-needed rain has begun to fall over Southern California, bringing relief to the drought-stricken region but also the threat of toxic runoff.

San Diego's dry conditions greatly increased the risk for wildfires. “We’ve been experiencing extreme fire behavior throughout Southern California as many have seen," said Rob Johnson, public information officer for CAL Fire.

If the rain falls at a steady, lighter rate, Southern California could be in good shape. That could mean enough rain to help ease the firefighting strain, but not enough to trigger another potential disaster. Heavier rain could mean the chance for flash flooding or mudslides over fresh burn scars.