@staticmethod
def atmospheric_pressure(z):
    """ Return the atmospheric pressure (:math:`P`) *[kPa]* as a function of the elevation above sea level as
        defined in `FAO 56 <http://www.fao.org/tempref/SD/Reserved/Agromet/PET/FAO_Irrigation_Drainage_Paper_56.pdf>`_
        (eq. 7, p. 31):

        .. math::

            P = 101.3\\left(\\frac{293-0.0065z}{293}\\right)^{5.26}

        The atmospheric pressure (:math:`P`) is the pressure exerted by the weight of the earth's atmosphere.
        Evaporation at high altitudes is promoted due to low atmospheric pressure as expressed in the psychrometric
        constant. The effect is, however, small and in the calculation procedures, the average value for a location
        is sufficient. A simplification of the ideal gas law, assuming :math:`20` *°C* for a standard atmosphere,
        can be employed to calculate :math:`P`
        (`FAO 56 <http://www.fao.org/tempref/SD/Reserved/Agromet/PET/FAO_Irrigation_Drainage_Paper_56.pdf>`_).

        :param z: elevation above sea level *[m]*
        :type z: float or np.array
        :return: (*float or np.array*) atmospheric pressure (:math:`P`) *[kPa]*
        """
    return 101.3 * ((293.0 - 0.0065 * z) / 293.0) ** 5.26
