code: def urban_adj_factor(self):
          
          urbext = self.catchment.descriptors.urbext(self.year)
          result = self._pruaf() ** 2.16 * (1 + urbext) ** 0.37
          self.results_log['urban_extent'] = urbext
          self.results_log['urban_adj_factor'] = result
          return result
docs: Return urban adjustment factor (UAF) used to adjust QMED and growth curves.
  
          Methodology source: eqn. 8, Kjeldsen 2010
  
          :return: urban adjustment factor
          :rtype: float