When any tract of land upon which any assessment has been levied is subdivided into smaller parcels, the board shall, upon its own motion or upon written application therefor signed by a landowner of record within the subdivided tract, after a hearing noticed and held in the same fashion as provided in Section 35520.10, reapportion the assessment upon the tract as will, in the judgment of the board, charge each of the smaller parcels with a just portion of the assessment. The reapportionment shall be entered in the minutes of the board and, upon entry, shall become final.