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

The rain that is expected to hit the scorched Los Angeles landscape this weekend may bring relief to the fire fights, but it could also bring flash floods and mudslides. Although forecasts show that the risk is relatively low, local officials are taking the warnings seriously.

With parts of Los Angeles County still smoldering from wildfires, the expected rain this weekend would seem like a welcome relief. But how the rain falls could make the difference between a disaster respite or a disaster repeat.