UPDATE ms_Catchment, msm_HModB
    SET ms_Catchment.Abflusswirksamkeit_pt = msm_HModB.AISteep + msm_HModB.AIFlat
    WHERE ms_Catchment.MUID = msm_HModB.CatchID;

UPDATE ms_Catchment
    SET ms_Catchment.AbflusswirksameFlaeche_ha = ms_Catchment.Area_C * ms_Catchment.Abflusswirksamkeit_pt / 100;

UPDATE ms_Catchment
    SET ms_Catchment.AbflusswirksameFlaeche_ha = ms_Catchment.Area * ms_Catchment.Abflusswirksamkeit_pt / 100
    WHERE ms_Catchment.Area IS NOT NULL;