Return urban adjustment factor (UAF) used to adjust QMED and growth curves.

        Methodology source: eqn. 8, Kjeldsen 2010

        :return: urban adjustment factor
        :rtype: float

def urban_adj_factor(self):
        """
        Return urban adjustment factor (UAF) used to adjust QMED and growth curves.

        Methodology source: eqn. 8, Kjeldsen 2010

        :return: urban adjustment factor
        :rtype: float
        """
        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