The rain began falling five days ago and is expected to intensify into early Wednesday. This may not sound like much to most readers but it is certainly something to be reckoned with in Southern California where very little rain falls each year.

Half a dozen Southern California counties are under an emergency declaration Wednesday as another powerful storm from the Pacific pummels the region.

“We’re preparing for what we expect to be a very heavy, severe rainstorm …” said Mike Kaspar with Los Angeles County Public Works. “In the worst-case senario, we could be looking at as much as 8 inches more of rain in the Southern California area.”

Forecasters warned of possible rainfall rates of 0.75 inch to 1 inch an hour and thunderstorm rates of 2 inches an hour in the region.

The five-day rain total has topped 10 inches in many areas, with much heavier amounts in some locales. More than 21 inches have fallen on Twin Peaks in San Bernardino county, with Twin Creek receiving nearly 20 inches.

Downtown Los Angeles received more than a third of its annual average rainfall in less than a week.

Mudslides are a significant risk for three years after a fire and are especially likely anytime the rainfall rate reaches or exceeds 1 inch per hour, said Susan Cannon, a research geologist with the U.S. Geological Survey.

That’s a likely scenario Wednesday in the area burned by last year’s Station Fire, which charred 250 square miles above the suburbs tucked below the San Gabriel Mountains.

“It means that once the heaviest rains start, it should be a very active time up there,” Cannon said.

Gov. Arnold Schwarzenegger has declared a state of emergency in Kern, Orange, Riverside, San Bernardino, San Luis Obispo and Tulare counties because of the storms.