def get_mean_class(mean_value):
    """Map mean value to risk level based on preset thresholds

    Parameters
    ----------

    mean_value : float
        the mean value of certain station
    
    Returns
    -------
    
    str
        the risk level
    """
    if mean_value < 0.2:
        return 'Zero'
    elif (mean_value >= 0.2) and (mean_value < 5):
        return 'Very Low'
    elif (mean_value >= 5) and (mean_value < 10):
        return 'Low'
    elif (mean_value >= 10) and (mean_value < 15):
        return 'Medium'
    elif mean_value >= 15:
        return 'High'
    else:
        return 'Zero'