Research On The Future Climate Change And Runoff Response In The Mountainous Area Of Yongding Watershed

Global climate change aggravates the hydrological cycle process and changes the spatial and temporal distribution pattern of water resources in river basins,which will bring greater challenges to water resources management and protection and sustainable use of water resources.The Yongding watershed is a vulnerable area of water resources and ecological environment in the semi-arid and semi-humid region of north China,which has low adaptability to climate change.It is of great significance to study the impact of climate change on the runoff in Yongding watershed to cope with climate change as well as strengthen the management and protection of water resources.In this paper,the mountainous area of Yongding watershed is selected as the study area.Based on the four GCMs with four core SSP-RCP combination scenarios in the CMIP6Scenario MIP,the characteristics of future precipitation and temperature changes were analyzed,and the runoff response under future climate change was simulated by SWAT model.The main research work and results are as follows:(1)Based on the data of watershed hydrometeorology,digital elevation model,land use and soil type,the SWAT model for the mountainous area of Yongding watershed was constructed with the consideration of the influence of human activities such as reservoir operation,irrigation water,industrial water and domestic water.Meanwhile,the model parameters were calibrated and verified by using the runoff data of 5 hydrological stations in the watershed.The R~2 and NSE of the calibration period monthly runoff simulation were both above 0.5,the R~2 in the verification period was above 0.5,and the NSE values were all above 0.5,indicating that the model has good applicability.(2)The Taylor plot was used to evaluate the applicability of GCM in CMIP6 in the mountainous area of Yongding watershed,and the results showed that the comprehensive simulation ability of the multi-model ensemble was the best.Stepwise multiple regression(SMLR)method and multicollinearity test were used to screen out the best independent variables,and SDSM model of meteorological elements in study area was established.The simulation effect of SDSM was better than that of precipitation.The R~2 and NSE of temperature were both above 0.92 in the calibration and verification periods,while the R~2 and NSE of precipitation were between 0.16 and0.60 in the calibration and verification periods.Quantile mapping(QM)method was used to correct the bias of multi-model ensemble data of downscaling simulation,and the precipitation and temperature after the bias correction can be improved to a certain degree.In particular,the simulated daily precipitation was closer to the measured value,and the precipitation probability distribution was greatly improved.(3)The trend of mean temperature,maximum temperature and minimum temperature under the four climate scenarios in the future is basically the same,showing an upward trend,and the change ranges are generally in the order of long term,medium term and short term,SSP585,SSP370,SSP245 and SSP126,respectively.The intra-annual changes of the three kinds of temperature are basically the same,among which June to September shows the most significant increase,followed by November to January.In terms of spatial distribution,the spatial distribution characteristics of the three future temperature of different climate scenarios are generally consistent with that in the reference period.The northeast region has the highest temperature,and shows a circular distribution,which gradually decreases outward.The temperature in the northwest region has a ring-shaped distribution,which increases from the northwest to the southeast.The mean temperature increases from the southeast to the northwest;the maximum temperature increases from the southwest to the northeast;as for the minimum temperature,there all shows circular distributions in the northwest,northeast and southeast regions,the difference is that the increase range in the northwest and northeast centers tend to decrease outward,while tend to increase outward in the southeast center.(4)The future precipitation will change drastically,the inter-annual precipitation fluctuates greatly,while the growth trend is not significant.The short-term precipitation is lower than that in the reference period,and the decrease order in different climate scenarios is SSP585,SSP370,SSP126 and SSP245,respectively.The precipitation of medium-term and long-term is higher than that in the reference period,and the increase order of different climate scenarios is SSP585,SSP370,SSP245 and SSP126,respectively.The intra-annual changes of precipitation in different climate scenarios is basically the same.On the whole,the change of precipitation from October to March is significantly larger than that of other months,and the increase of precipitation from January to March is the most significant.The spatial distribution of precipitation in different climate scenarios is quite different.Under the SSP126 and SSP245 scenarios,the increase range in precipitation rises from northwest to southeast.The area where the precipitation increases enlarges in the southeast and southwest of the watershed over time.Under the SSP370 and SSP585 scenarios,the short-term precipitation increases from the southwest to the northeast,and the spatial distribution of precipitation is high in the east and low in the west.The spatial distribution of the medium-term precipitation is roughly consistent with that in the reference period,which increases from the northwest to the southeast.The long-term precipitation decreases from the southwest to the northeast,and the spatial distribution of precipitation shows characteristics of high in the west and low in the east,and high in the south and low in the north.(5)The constructed SWAT model was used to simulate the change of runoff under four climate scenarios in the future,and the future runoff under each climate scenario showed an increasing trend.The short term increase order of runoff under different climate scenarios is SSP245,SSP370,SSP585 and SSP126,respectively.The increase order of medium and long term climate scenarios is SSP585,SSP370,SSP126 and SSP245,respectively.The simulated future annual runoff of the watershed will increase compared with that in the reference period,and the monthly runoff will increase significantly compared with that in the reference period under different climate scenarios in the future three periods,especially under SSP585 scenario.The increase of runoff in dry season(December to April)is greater than that in wet season(July to October).The spatial distribution characteristics of runoff under different climate scenarios are generally consistent with that in the reference period.Compared with other regions,the runoff in northwest,northeast and southeast regions is more abundant,and the future runoff will significantly increase in southwest and southeast regions,especially under SSP370 and SSP585 scenarios.