def discomfort_index(ta, rh):
    """Calculate discomfort index (DI) from air temperature and relative
    humidity.

    Discomfort Index is derived from original work carried out by Eral C. Thom
    [1] which defined discomfort index based on dry-bulb and wet-bulb
    temperature. It is the human-perceived increase in air temperature due to
    humidity increase.

    Note:
        [1]  Thom, E.C. (1959) "The Discomfort Index". Weatherwise, 12, 57-61.

    Args:
        ta: Air temperature [C]
        rh: Relative humidity  [%]

    Returns:
        di -- Discomfort index [C]
    """
    di = ta - (0.55 - 0.0055 * rh) * (ta - 14.5)
    return di
