code: def wateryear(self):
          
          if self.month < self._firstmonth_wateryear:
              return self.year
          return self.year + 1
docs: The actual hydrological year according to the selected
          reference month.
  
          The reference mont reference |Date.refmonth| defaults to November:
  
          >>> october = Date('1996.10.01')
          >>> november = Date('1996.11.01')
          >>> october.wateryear
          1996
          >>> november.wateryear
          1997
  
          Note that changing |Date.refmonth| affects all |Date| objects:
  
          >>> october.refmonth = 10
          >>> october.wateryear
          1997
          >>> november.wateryear
          1997
          >>> october.refmonth = 'November'
          >>> october.wateryear
          1996
          >>> november.wateryear
          1997