Cal. Wat. Code § 51346.5
If the valuation assessment commissioners have utilized land use categories as a basis for the assessment valuation pursuant to Section 51324.5, the board may, without petitioning for the preparation of a new roll under Section 51346, adjust, not more often than annually, the assessment valuations for each parcel of land or subdivided parcel of land within district boundaries to reflect changes in the land use category or type of land use category shown for that parcel on the records of the county assessor, in order to conform to the category currently shown on the records of the county assessor for the respective parcel, in conformity with the report of the commissioners. Any such adjustment to the assessment valuation shall be accomplished by the preparation and filing of a supplement to the operation and maintenance assessment roll to be filed in accordance with Section 51337 upon which shall be endorsed the statement "Adjusted to reflect changes in land use as of (date)."
Ca. Water Code § 51346.5