N.H. Rev. Stat. Ann. § 231:122

In order to defray the costs of the operation and maintenance of such public facilities, the assessors may assess upon the owners and lessees whose land is benefited by such public parking facilities their just share of the annual operating expenses of the same. The assessors may establish a scale of assessments and prescribe the manner in which and the time at which such assessments are to be paid and to change such scale from time to time as may be deemed advisable.