Abstract:By calculating and comparing effects of condensation heating, modified moist-ageostrophic Q vector (Q*), and topographic forcing among three categories of heavy rainfall: heavy rainfall(R1), large heavy rainfall (R2), and extremely heavy rainfall (R3), the cause of rainfall intensity difference associated with typhoon Haitang (2005) is analyzed quantitatively. The results show that latent heating contributes to differences in intensity between R1 and R2 during the whole landfall, and among three rainfall categories after the landfall. The forcing from Q* vector accounts for differences in intensity between R1 and R2 before the landfall while it contributes to differences in intensity among three rainfall categories after the landfall. The topographic lifting is responsible for differences in intensity among R3 and R2,R1 before the landfall whereas it contributes to differences in intensity among three rainfall categories after the landfall.