When hills are healthy, vegetation can anchor the soil in place. But when that is burned off, hillsides become vulnerable to erosion, and slopes can come crashing down.

Forecasters released a breakdown Tuesday of where and when heavy rainfall this week is expected to hit areas of Southern California left burn-scarred by recent wildfires, raising the risk of potentially dangerous debris flows in those parts of the region.

Residents in burn scar areas should be ready to evacuate if needed. City and county agencies have readied streets for debris flow with K-rails and sandbags, as a storm moves in on Wednesday, Feb.