Runoff Simulation Of The Lanjiang River Basin And Future Climate Change Response

The Intergovernmental Panel on Climate Change claims that the early 21st century has become the hottest period on record globally.Currently,warming-induced extreme climatic and hydrological events is increasing,which has become an important factor that restricts social-economic sustainability goals in China,and the environmentalists commonly focuses on the climate warming issues globally.The Lanjiang River Basin locates in the upper reaches of the Qiantang River Basin where more than 50catastrophic floods historically occurred,which is the key area of flood controlling in the Zhejiang Province.Due to climate change and human activities,the frequency of floods occurrence in recent years has increased to once every four years thus causing socioeconomic losses.Assessing the impact of future climate change on hydrology and water resources could assist in decision making about hydraulic project planning and water management.Taking the Lanjiang River Basin as a case study,this study established the SWAT（Soil and Water Assessment Tool）hydrological model,HEC-HMS hydrological model,the SDSM statistical downscaling model and Can ESM2climate model to analyze hydrological changes in response to projected future climate scenarios.The main conclusions were summarized as follow:（1）The SWAT hydrological model and HEC-HMS hydrological model were both successfully applied in the Lanjiang River Basin.The simulation results are evaluated by a variety of evaluation indices at a daily scale.The results of all indexes showed that h the SWAT model and HEC-HMS model both could accurately simulate the runoff changes implying that these two models were capable of the water resources’responses to future climate change in the study area.In conclusion,the simulation accuracy of the SWAT model is better than that of the HEC-HMS model,and the simulation accuracy for the Lanxi hydrological station is better than that of the Jinhua and Quzhou hydrological stations.（2）The changes in temperature and precipitation variables both showed obviously increasing trends,and the magnitude increased with the enhancement of radiation forcing.The SDSM statistical downscaling model and Can ESM2 climate model were used to predict the future trends of temperature and precipitation in the Lanjiang River Basin under the RCP2.6,RCP4.5 and RCP8.5 scenarios.The results showed that under the RCP2.6 scenarios,the maximum temperature and minimum temperature both increased gradually to the maximum and then decreased,and the precipitation exhibited a slight downward trend.Under the RCP4.5 and RCP8.5 scenarios,the maximum temperature and minimum temperature both continuously increases,and the precipitation first declined and then increased.By the end of the 21st century,the maximum and minimum temperatures will have increased by 0.04℃-3.18℃compared with the base period,and the precipitation will have increased by-0.98%-38.08%compared with the base period.（3）The runoff of the Lanjiang River Basin was projected to increase in the future,and will increased with the increases of radiation forcing.The temperature and precipitation data under different scenarios simulated by the SDSM model were input into the SWAT hydrological model to analyze the future runoff changes under different climate scenarios.The results indicated that the annual runoff under three RCPs scenarios showed different trends.Under the RCP2.6 scenarios,the runoff increased gradually to the peak value and then become stable.Under the RCP4.5 scenarios,the runoff increased gradually to the peak value and then decreased.Under the RCP8.5scenarios,the runoff increased continuously.By the end of the 21st century,the annual average runoffs under the three scenarios reached 713.57 m³?s^-1,665.39 m³?s^-1 and1153.52 m³?s^-1,respectively.Compared to baseline monthly runoff,the monthly runoff in the wet seasons increased significantly higher than that in the dry seasons,with the largest increase in March and July.Monthly runoff will increase in accordance with the enhancement of radiation forcing.The runoff in wet season will increase in the future,indicating an increase of flood frequency in the future wet seasons due to climate change.