Study On The Response Of The Hydrological Process Of The Jinsha River Basin To Climate Change Based On The SWAT Model

The Jinsha River is the upper reaches of the Yangtze River,China's largest river,which is rich in water resources and hydropower resources,and it is also a major component of floods in the upper and middle reaches of the Yangtze River.Under the background of global and regional climate warming,the spatial-temporal transformation of the water cycle in the Jinsha River Basin will change,which may lead to uneven spatial and temporal distribution of precipitation and water resources,and increase the occurrence and intensity of hydrological extreme events such as droughts and floods.This paper took the Jinsha River basin as the research object and analyzed the characteristics of the changes of the hydrological cycle elements by the three methods of comprehensive analysis of Kendall rank correlation method,the Spearman rank correlation method and linear trend regression,and the method of cumulative anomaly and Mann-Kendall mutation test.At the same time,the SWAT hydrological model was used to construct the watershed model,through model sensitivity analysis and applicability evaluation,the calibrated model was applied to the hydrological simulation study of the Jinsha River basin.Considering the disturbance factors such as precipitation,temperature,and solar radiation,a total of 100 different climate changes were set.The trend of future runoff,actual evapotranspiration,and soil moisture content and their response to disturbance factors were analyzed.The main conclusions are as follows:?1?According to the meteorological statistics from 1970 to 2012,it is estimated that the average annual precipitation in the Jinsha River basin is about 617mm,and the average annual temperature in the basin is about 9?.The average annual radiation in the basin is about 16 MJ/?m²·d?.The distribution of precipitation season in the Jinsha River basin was obvious.The precipitation from May to October accounted for more than 80%of the annual precipitation,of which the largest proportion was from July to August.?2?The average annual precipitation and annual average temperature in the Jinsha River Basin during the period from 1970 to 2012 both showed an increasing trend within the study time range.The annual average solar radiation showed a decreasing trend,and the average temperature and solar radiation showed significant interannual changes.Cumulative anomaly mutation test revealed that the annual average rainfall abrupt change year was 1997;the annual average temperature abrupt change year was1997;the annual average solar radiation abrupt change year was 1988.?3?The extremum ratio?K_m?,coefficient of variation?C_v?,non-uniform coefficient of distribution within runoff year?C_i?,and annual adjustment coefficient of annual runoff distribution?C_r?were calculated respectively for the upstream and downstream hydrological control stations?Shigu Station,Panzhihua Station,and Pingshan Station?,to reflect the characteristics of the runoff during the year.The results showed that the interannual variation of runoff in the Jinsha River Basin was not significant,and the degree of change from the upstream to the downstream of the entire watershed was almost the same,and there was a certain degree of non-uniformity in the distribution of runoff during the year.The runoff of the Shigu Station,Panzhihua Station,and Pingshan Station did not pass the 95%confidence test,and the interannual change was not significant,and which showed an increasing trend within the study time frame.The cumulative anomaly method and the Mann-Kendall mutation test method were used to analyze the runoff of the three hydrological control stations.The results showed that:the annual runoff abrupt change years at Shigu Station were in 1986 and 1995;the annual runoff abrupt changes at Panzhihua Station were in 1986 and 1997;the annual runoff abrupt changes at Pingshan Station were in 1984,2005,and 2008.?4?The SWAT-CUP?2012 version?software is used to determine the parameters by using the built-in SUFI-2 algorithm,the daily and monthly scale runoff data of the hydrological station of the Shigu hydrological station,Panzhihua hydrological station and Pingshan hydrological station from 1973 to 1997 were selected to simulation respectively along the upstream to exit of the Jinsha River Basin.The conclusions are as follows:The simulations of the monthly scale at the three hydrological stations are better than those at the daily scale.In the monthly time scale,runoff data from 1973 to1987 were used for model calibration,and runoff data from 1988 to 1997 were used for model validation.The model warm-up period was 1970 to 1972.The evaluation results for the calibration period and validation period were as follows.The calibration period was:the Shigu hydrological station R²=0.84,E_ns=0.65;the Panzhihua hydrological station R²=0.89,E_ns=0.85;the Pingshan hydrological station R²=0.93,E_ns=0.92;the validation period was:the Shigu hydrological station R²=0.85,E_ns=0.64;the Panzhihua hydrological station R²=0.86,E_ns=0.82;the Pingshan hydrological station R²=0.92,E_ns=0.90.The accuracy of the two parameters satisfies the model simulation requirements,indicating that the SWAT model is applicable to the Jinsha River basin.?5?Applying a well-established SWAT model,assuming a total of 100 climate scenarios?including the basic scenario?of the combination of precipitation,temperature and solar radiation changes,analyzing the trend of future runoff,actual evapotranspiration,and soil moisture content and their response to disturbance factors were analyzed.The results showed that the sensibility of runoff,actual evapotranspiration and soil moisture three to the change of precipitation was higher than that of temperature and solar radiation.The runoff was positively correlated with precipitation and negatively correlated with temperature and solar radiation,the Pingshan Station as an example,When the temperature T and the solar radiation R_s were kept in line with the reference period,the annual average runoff decreased by538.11m³/s?21.16%?when the precipitation P decreased by 10%.The actual evapotranspiration was positively correlated with precipitation,air temperature,and solar radiation.When the temperature T and solar radiation R_s were kept consistent with the reference period,and the precipitation P increased by 10%,the annual average actual evapotranspiration increased by 1.62mm?4.37%?.The soil moisture content was positively correlated with precipitation and negatively correlated with temperature and solar radiation.When the temperature T and solar radiation R_s were kept consistent with the reference period,and the precipitation P decreased by 10%,the annual average soil moisture content of the basin decreased by 15.22mm?16.34%?;At the present stage,based on the number of built water conservancy projects in the Jinsha River,the utilization pattern of basin water resources,and the condition of the underlying surface of the basin are stable,future changes in precipitation are the main factors affecting the changes in runoff,actual evapotranspiration,and soil moisture content.?6?The qualitative and quantitative analysis of the extreme climate scenarios S16,S20,S96,and S100 out of the 100 climate scenarios were compared with the annual average runoff,actual evapotranspiration,and soil moisture content in each sub-basin during the reference period.The results showed that:The soil moisture content and runoff of each sub-basin were most sensitive to the above-mentioned extreme climate scenarios,with the large proportion of change,and the change degree of the actual evapotranspiration was slightly weaker.The trend of the overall spatial distribution of annual average flow,actual evapotranspiration and soil moisture content in each sub-basin of the four different extreme climate change scenarios were basically consistent with the reference period.