def _sat_vapor_pressure(temperature):
    """Saturation vapor pressure from temperature (Eq. 7)

    Parameters
    ----------
    temperature : ee.Image
        Air temperature [C].

    Returns
    -------
    e : ee.Image
        Saturation vapor pressure [kPa].

    Notes
    -----
    es = 0.6108 * exp(17.27 * temperature / (temperature + 237.3))

    """
    return temperature.add(237.3).pow(-1).multiply(temperature)\
        .multiply(17.27).exp().multiply(0.6108)
    # return temperature.multiply(17.27).divide(temperature.add(237.3)).exp()\
    #     .multiply(0.6108)