def UC_Q(Q_mmd, A_catch):
    """ Convert discharge from units of mm/day to m3/day

    Args:
        Q_mmd:   Float. Discharge in mm/day
        A_catch: Float. Catchment area in km2

    Returns:
        Float. Discharge in m3/day
    """
    Q_m3d = Q_mmd*1000*A_catch
    return Q_m3d