Future Precipitation And Temperature Simulation Of Han River Basin With NEX-GDDP Data Set And SVR-QM Method

Climate warming causes more and more frequent extreme climate events.Therefore,future climate change has become a research hotspot.After NASA released the high-resolution NEX-GDDP data set,it is more important and feasible to use the data set to simulate and project the local climate of Hanjiang River Basin,and it is of guiding significance to flood control and disaster reduction,water resource allocation and economic development of the basin.Based on the historical precipitation,maximum and minimum temperature data of Hanjiang River Basin and 21 NEX-GDDP corresponding data sets,considering the highly nonlinear simulation ability of support vector regression(SVR)for climate factors and the superiority of quantile mapping method(QM)for deviation correction,this paper proposes and establishes the support vector regression quantile mapping(SVR-QM)ensemble and correcting models.Then,using the SVR-QM model driven by NEX-GDDP data under the scenarios of RCP4.5 and RCP8.5,the projection of rainfall,maximum and minimum temperature in the 21 st century in Hanjiang River Basin under the two scenarios are obtained,and then the change trend is analyzed.Finally,a series of extreme rainfall and temperature indexes are used to evaluate the temporal and spatial characteristics of future extreme rainfall and temperature in Hanjiang River Basin.The main research contents and results are as follows:1.The simulation of historical rainfall and temperature based on NEX-GDDP data and SVR-QM method.Firstly,the optimal SVR simulation method is selected from MLP,SVR and RF.Furthermore,the quantile mapping method is used to correct the deviation,so as to reduce the deviation.The results show that a single NEX-GDDP model is reliable for the simulation of historical precipitation,maximum and minimum temperature data.For rainfall and maximum and minimum temperature,SVR-QM method is superior to three machine learning ensemble simulation methods and simple ensemble average results.The PCC of rainfall increased to 0.84,RMSE decreased to 33.82 mm,and the PCC of maximum and minimum temperature increased to 0.94-0.95 respectively.And RBias decreased significantly.The RBias value of each station decreased from-2.04%-0.36% to-0.03%.For stations,most of them have similar conclusions with regional average.2.Coupled with NEX-GDDP data and SVR-QM for future rainfall temperature simulation.Then,we use(Manner-Kendall)MK trend test,QQ chart and other technologies to analyze the trend of data under the two scenarios.It can be seen that under the scenarios of RCP4.5 and RCP8.5,the regional mean precipitation in the21 st century generally shows a weak growth trend,and the latter is more obvious.Among them,the average precipitation in the middle and later period of the 21 st century increased by 3.23% and 1.02% respectively compared with the reference year of RCP4.5;the reference year of RCP8.5 increased by 4.25% and 8.30% respectively,and the change range in winter and spring was higher than that in summer and autumn.Under the scenario of RCPp4.5,the increase range of precipitation in the basin gradually decreased from the Northwest Mountainous area to the southeast.Under the scenario of rcp8.5,the increase range of precipitation in the upper northwest region was significantly larger than that under the scenario of RCP4.5.The annual average temperature of Hanjiang River Basin shows a significant warming trend of 0.13 and0.39 ° C / 10 a in 2020-2099,which is 1.53 and 2.21 ° C higher than that in 1981-2000.The future change of the maximum temperature in the basin is shown in two scenarios,the overall performance is that the mountain area in the upper reaches is higher than the plain area in the lower reaches;the overall change trend of the minimum temperature is consistent with the maximum temperature,but in the RCP4.5 scenario,some areas in the upper reaches show weak warming,which is obviously inconsistent with other areas.3.Coupling NEX-GDDP data and SVR-QM to simulate the trend of extreme climate change.In this paper,a series of extreme rainfall(R95,SDII,R20 m,Rx1day and Rx5day)and extreme temperature indexes(FD,SU,TNn,TXx and DTR)are used to evaluate the temporal and spatial characteristics of extreme rainfall and temperature in the future in Hanjiang River Basin.The results show that under the scenarios of RCP4.5 and RCP8.5,most of the extreme precipitation indexes will increase in the future,especially in the late 21 st century.The occurrence of extreme precipitation events shows strong regional characteristics.Especially under the RCP8.5 scenario,the variation range of the upper and middle reaches of the Han River is close,and is significantly higher than that of the lower reaches of the Han River,and the variation trend of the moderate rainfall intensity in the Han River Basin is the smallest.Under the two emission scenarios,FD,Su,TNn and TXx showed significant warming trend in 2020-2099,especially in rcp8.5,with the change range of-1.44,4.48 days / 10 a and 0.44,0.47 ° C / 10 a.In terms of spatial distribution,the extreme temperature indexes under the two scenarios show a relatively consistent warming trend in the upper,middle and lower reaches of the Hanjiang River,but there are obvious regional differences in the range of change.The stations of FD,SU,TNn and TXx are all concentrated in the upper and middle reaches of Hanjiang River.For DTR,the increase trend of the upper reaches of Hanjiang River is the most obvious.