You are correct in raising a concern about an insurer unilaterally changing the application of a rating factor. That is not allowed in California.
I am assuming the 160% increase your are citing is the difference between your premium last year and the premium on your renewal. Then the question would be: Has the insurer received approval of a rate filing by the California Department of Insurance (CDI) in the last 12 months that changed how your home was rated?
I think you’re going to need to file a complaint with the CDI to get that answer.
I am also noting that you are asserting the cause in the increase is due to an inaccurate estimation of your flooding risk. But homeowners policies don’t cover the peril of flood. Water risk is a significant concern for insurers – but typically rate factors focus on the age of the plumbing in the home or a previous plumbing related loss. Generally, those don’t explain a 160% increase.
If the premium increase is legitimate then something must have changed in your insurer’s rating plan for a premium increase of that magnitude to be approved. (Again, if it was approved). In recent years, most triple digit increases are limited to homes with the highest wildfire risk scores. So ask the CDI to explain to you how your premium increase was justified (if it was approved).
You didn’t name the insurer and my response is based on the premise it’s an admitted insurer, not a surplus lines/nonadmitted insurer. The latter can increase their premiums at renewal without CDI approval.
Regardless, though it’s a very challenging homeowners insurance marketplace, and you should shop around for a less expensive option. If you can’t beat the price, at least you’ll know your insurer is still in the range of reasonable compared to others.