def evap_fract_stiver_mackay_integr(henry, theta_wtt):
    """
    Return the evaporated fraction by unit of time  [1/s],
    consider the area constant
    source:(Stiver and Mackay, 1984)

    Parameters
    ----------
    henry : Henry constant []
    theta_wtt : Theta without the time [1/s]

    """
    return henry * theta_wtt