calculate_wrf_bc Module Function

    module function calculate_wrf_bc(self, h) result(theta_w)
        implicit none
        class(type_wrf_bc), intent(in) :: self
        real(real64), intent(in) :: h
        real(real64) :: theta_w

        if (h < self%alpha1) then
            theta_w = self%theta_r + (self%theta_s - self%theta_r) * (self%alpha1 / h)**self%n1
        else
            theta_w = self%theta_s
        end if

    end function calculate_wrf_bc