Study On Flood Response Difference Between Typhoon And Non-typhoon Rainstorm Under Changing Environment

Rainstorm is the main factor of flood generation,which affects the process of flood generation and confluence together with underlying surface conditions.The southeast coastal areas of China are affected by tropical cyclones such as monsoon and typhoon,so the floods generated by typhoon rainstorm can be called typhoon rainstorm floods,and the floods generated by other non-typhoon rainstorm can be classified as non-typhoon rainstorm floods.The results show that there are differences in flood response between typhoon and non-typhoon rainstorm.Therefore,does the difference in flood response between typhoon and non-typhoon rainstorm also lead to the difference in response to land use change,and then affect the impact of land use change on flood frequency?Is it possible to better reveal the impact of climate change and human activities on typhoon and non-typhoon storm floods by distinguishing typhoon and non-typhoon rainstorm floods and analyzing the change of flood trend in changing environment respectively?Therefore,taking the Xixi watershed of Jinjiang river in southeast China as a typical area,the following aspects were studied:(1)HEC-HMS models of typhoon and non-typhoon rainstorm flood were constructed respectively,and the flood response differences between typhoon and non-typhoon rainstorm were analyzed through the changes of model parameters;(2)The impact of land use change on typhoon and non-typhoon storm floods was analyzed by using the model,and the corresponding frequency analysis was conducted to discuss the difference of the impact of land use change on typhoon and non-typhoon storm floods.(3)In order to explore the difference in the trend response of typhoon and non-typhoon storm floods under the changing environment,the trend analysis was carried out on the measured and the restored annual maximum typhoon rainstorm flood,non-typhoon rainstorm flood and the undifferentiated flood series during 1964-2015.The results show that:(1)HEC-HMS model has strong applicability to both typhoon and non-typhoon rainstorm floods in Xixi basin of southeast China.The average efficiency coefficients of both calibration and verification periods were above 0.7.(2)The variation patterns of key parameters of typhoon and non-typhoon rainstorm flood models were systematically different.The initial loss rate and wave velocity of typhoon rainstorm floods were significantly higher than those of non-typhoon rainstorm floods.The empirical correlation coefficients between initial loss rate and initial discharge were 0.956and 0.964,the empirical correlation coefficients between wave velocity and rain intensity were 0.899 and 0.916 respectively.(3)There are significant differences in the responses of typhoon and non-typhoon rainstorms floods to land use change.Compared with the results that do not distinguish the types of floods,the impact of land use change on typhoon rainstorm floods is overestimated and the impact on non-typhoon rainstorm floods is underestimated.After distinguishing the flood types,it is found that the flood effect of land use change is more reasonable.In the case of the same magnitude of flood,the increase of peak flow of non-typhoon storm flood caused by land use change is larger than that of typhoon storm flood,and the difference is bigger with the increase of flood magnitude.(4)The main effect of land use change on flood frequency is that the mean peak discharge value increased from 2266.56m~3/s to 2510.19m~3/s,the values of Cv were slightly altered and those of Cs/Cv were unchanged.(5)Distinguishing typhoon from non-typhoon rainstorm could better reveal the changing trend of flood.Under the changing environment,the flood of the largest typhoon rainstorm flood in the past year does not rise significantly,but the flood of non-typhoon rainstorm flood descended significantly,while the undifferentiated maximum flood of the calendar year decreased slightly.(6)The decrease in rainfall caused by climate change is the main factor for the decline in the trend of non-typhoon rainstorm floods,the increase in rainfall and rain intensity dominates the trend of typhoon rainstorm floods under changing environments,the influencing factors of the trend change of the undifferentiated flood series are complex,the increase of air temperature and the decrease of soil moisture content may be the main reasons for the decline of the trend of undifferentiated floods.