Impact Of Climate Change And Human Activities On Hydrological Processes In Upper Reaches Of The Yangtze River Basin

The main characteristics of hydrological process are regional and comprehensive.Regionality refers to the existence of regional differences and regional differentiation in watersheds.Comprehensiveness refers to the study of the interaction of various elements of watershed ecosystems and man-land relationship,so as to help us understand the history,current situation and future of watershed ecosystems.Based on the long-term field observations,model simulations,and the set combination of climate change and human activities,coupling of patterns and process,this paper quantitatively studied the impact on climate change and human activities on hydrological processes at different stages,found and understood the response to the hydro-ecological of the watersheds to climate change and human activities,so as to promote the harmonious development of ecology,economy and society of the water-ecological environment and management of water resources.Therefore,the upper reaches of Yangtze River Basin(UYRB)was selected as research area in this study.The data including the measured data,the rainfall,temperature,runoff,sediment transport and water level were analyzed in three stages from 1972 to 2016 and the methods including Sen's Slope and Mann-Kendall test were selected to analyze the changing trends of meteorological and hydrological data based on above data.The terrain database,land use database,soil map data,meteorological data,hydrological data,etc.required for Soil&Water Assessment Tool(SWAT)model were established.The SWAT model is parameter-determined and model-validated according to different stages,and the validated SWAT simulation was used.Quantitative analyzing of the contribution to which human activities affect hydrological elements,the contribution to which climate change affects hydrological elements and the comprehensive contribution to which human activities and climate change,i.e."contribution rates",by setting a portfolio for seven programmes for human activities and climate change,simulated the surface ecohydrologic process of runoff in the basin and analyzed the spatial and temporal patterns and trends;the model also simulated the spatio-temporal pattern and trend analysis of soil erosion in the upper reaches of the Yangtze River basin,and finally analyzes the effects of different future scenarios on ecological hydrological processes according to the four different land-use scenarios(FW,PR,MF and GT)and the three climate scenarios(RCP 2.6,RCP 4.5 and RCP 8.5).Hydrological responses were analyzed.The conclusions were as follows:The climate spatio-temporal pattern and trend of UYRB,the spatial datasets of annual,seasonal and monthly precipitation,average temperature,maximum temperature and minimum temperature in the upper reaches of the Yangtze River Basin are obtained based on the Delta downscaling method,with a spatial resolution of?1km.1972-2016 was divided into three stages using 1992 and 2001 time nodes,and Sen's slope and Mann-Kendall non-parametric test were used,the grid point unit with resolution of 1km×1km as the data carrier,basic evaluation and analysis unit of each climate factor to comprehensively analyze the climate change in the upper reaches of the Yangtze River Basin,and the spatial-temporal pattern and future trends of the climate factors in the upper reaches of the Yangtze River basin are controlled by the overall and spatial internal differences.The main conclusions are as follows:1)We found that the precipitation was significantly increased in the upper reaches of the Yangtze River basin in 45 years,and the precipitation trend in the Jinsha River basin increased first and then decreased,while the precipitation trend in the Mintuojiang River basin,the Pingshan-Cuntan Zone,the Wujiang River Basin,the Cuntan-Wan County Zone,the Wancounty-Yichang Zone and so on showed first decrease and then increased.2)Spring and summer precipitation trend increased and the increased trend was significant in the UYRB,the precipitation trend was decreased in autumn,the decreased trend was significant,and the precipitation trend was not significant in winter.The distribution of precipitation was unevenly distributed in the UYRB during the year,and precipitation between the spring,summer and autumn periods accounts for nearly70%of the total annual precipitation.3)The average temperature,maximum temperature and minimum temperature spatial pattern of the UYRB are similar.The average annual temperature value in the last 45 years was between 7.3?.The average annual minimum temperature was 2.2?,and the average annual maximum temperature was 12.5?.The focus on the hydrological elements and soil erosion spatio-temporal pattern and trend of UYRB based on the hydrological and soil erosion time-series data combined with RS and GIS,revised RUSLE model,Sen's slope and Mann-Kendall non-parametric test were established and spatial explicit expression of the annual change and inter annual change trend of runoff,sediment transport,water level,and the distribution change,and also analyzes the spatial-temporal distribution change of soil erosion and the relationship between soil erosion intensity and topographical factors.The main conclusions are as follows:1)The surface runoff was at a low level overall in the UYRB,with the region significantly reduced accounting for 34 percent of the total area in the UYRB and 8.7 percent of the total area in the UYRB.Total runoff in the basin decreased at 1.47 mm per year.2)The average annual sediment transport in45 years was 220 million t·a^-1.The sediment transport in Zhutuo station,Wanxian station and Miaohe station decreased significantly(P<0.05),while that in Batang,Gaoyang,Beibei,Wulong,Wuxi,Huanglingmiao and Yichang increased significantly(P<0.05);from 1972 to 1992,the runoff of Baihetan,Gaoyang,Beibei,Wulong,Wanxian,Wuxi,Miaohe and Huanglingmiao stations decreased significantly(P<0.05),while Baihetan and Zhutuo stations increased significantly(P<0.05);from 1993 to2001,the Baihetan and Miaohe decreased significantly in sediment transport(P<0.05),while that in Huatan showed a significant increase(P<0.05).The sediment transport of other stations failed to pass the 95% confidence level,and were not significant;from2001 to 2016,the water levels of Batang,Panzhihua,Baihetan,Huadan,Beibei,Wuxi,and Huanglingmiao stations showed a significant decrease,and the water levels of Cuntan,Wulong,and Miaohe stations showed a significant increase(P<0.05).4)soil erosion was mainly dominated by light erosion and the topography has a greater influence on the distribution of soil erosion in the UYRB.The annual soil erosion shows decreased trend.Soil erosion in the watershed mainly occurs within the slope of 6°—15°,accounting for 66.29%of the total soil erosion.It is an important area for preventing and controlling soil erosion.Therefore,it is necessary to strengthen the management of land resources and increase the control of soil erosion.In order to quantitatively identify the contribution of human activities and climate change to runoff,and predict the future impact of climate change and human activities on runoff,firstly,this paper set seven historical climate change and human activity combinations based on 1992 and 2001 time nodes.The quantitatively identifies the impact of climate change and human activities on runoff.Secondly,using the SWAT model verified in the natural stage,according to the setting of three future climate scenarios and four future land use scenarios,the degree of analysis of the impact of climate change and human activities on hydrology during 2041-2060 were predicted.The change between the first period(1972-1992)and the second period(1993-2001)was P1 Period,and the change between the second period(1993-2001)and the third period(2001-2016)was P2 Period.The results are as follows:1)During the P1 stage,climate change caused a decrease in runoff,and human activities led to a decrease in runoff in the UYRB.The“contribution rate”of climate change to runoff was close to90%;during the P2 stage,climate change caused an increase in runoff,human activities also caused an increase in runoff,and the impact of human activities was obvious.The"contribution rate"of the impact of human activities on runoff was close to 50%,and its impact may increase in the future.2)Compared with the future runoff data to the reference period runoff data,the runoff simulation values of the four future scenarios are reduced to different degrees,and the runoff variation under RCP 4.5 was greater than that of RCP 2.6 and RCP 8.5.FW and GT will be more affected by future climate scenarios under future land use scenarios,and RCP 8.5 will have a greater impact on runoff under GT land use scenarios.3)the influence of grassland and cultivated land on soil erosion is obvious in the study area,and the soil erosion in the future shows an increasing trend.The increasing rate of soil erosion from large to small are scenario FW>scenario pr>scenario MF>scenario GT,and the increasing rates are 50.19%,37.67%,35.89%and 8.22%,respectively.The future soil erosion shows an increasing trend.The main innovations points as follows:1)Based on Delta downscaling method and data fusion method,a long time series data set of key climate factors with spatio-temporal consistency is constructed.Combined with Mann-Kendall nonparametric test method,Sen slope estimation method and other statistical methods,spatial explicitly expressed the phased the spatio-temporal patterns and trend changes of key climate change factors.2)Based on the hydrological statistical method,the variation characteristics of hydrological elements in the upper reaches of the Yangtze River were analyzed,and the pattens changes and trends were recognized.Meanwhile,the revised RUSLE model was used to quantitatively analyze the long-term series of soil erosion,spatial distribution characteristics and trend changes in the upper reaches of the Yangtze River.The relationship between soil erosion intensity and terrain factors was also analyzed.3)Climate change coupling wiht human activities has affect the large-scale hydrological process in the upper reaches of the Yangtze River basin.Based on distributed hydrological models and empirical models,the impact degree and change trend of climate change and human activities in stages on hydrological processes in the upper reaches of the Yangtze River were quantitatively studied,and the impact of climate change and human activities on hydrological processes in the upper reaches of the Yangtze River was simulated on the basis of future climate change and land use changes,so as to predict the"contribution rate"of future climate change and human activities to hydrological processes.