Synergistic Response Of Runoff To Climate Change And Land Use Change In The Upper Sancha River Basin Of Guizhou Province

The upper basin of Sancha River in Guizhou Province is located in the deep canyon area of karst plateau in the sloping zone of Yunnan-Guizhou Plateau,where carbonate rocks are widely developed and water and soil erosion are serious.As a tributary of the southern source of Wujiang River,the dynamic change of water resources has a profound impact on the water security in central Guizhou,so it has extremely important social ecological value and strategic significance of economic development.Sancha River upstream watershed was chosen as the research object in this study,the history and expected climate change in the future were analysed The characteristics of land use change in the past and the future was also discussed.SWAT hydrological model is suitable for the karst basin,analysis of the historical period quantitative influence of climate change and land use on runoff,explore the future may face in the runoff change scene,The coupling response mechanism of runoff to climate change and land use change was revealed by evaluating the impact of different land use types on water balance in the watershed.The research results provide theoretical reference for the development,utilization and protection of water resources in karst watershed of southwest China.The main results are as follows:(1)The climate change in the upper Sancha River basin presents the following characteristics:from 1980 to 2017,the average annual rainfall in the basin is 1146.05mm,and fluctuates at a rate of 20mm/10a.1980-1990and 1991-2006 were wet periods,indicating that the average annual rainfall in this period was higher than the average rainfall in the whole period.2007-2017 was dry periods,but with an increasing trend.The average annual temperature of the basin is 13.82?,and the warming rate is0.4?/10a.During 1980-2000,the average annual temperature is dominated by negative anomalies,while during 2001-2010,the average annual temperature is dominated by positive anomalies,indicating that the change of average annual temperature in the whole period has experienced from stable slow growth to fluctuating growth.To a process of steady and rapid growth.In the future period(2020-2099),the precipitation of different scenarios(RCP45 and RCP85)showed a trend of continuous fluctuation,with the growth rate of 15.5mm/10a in RCP45 scenario and 17.4mm/10a in RCP85 scenario,but with obvious stages.It shows that the trend changes tend to be mild after 2060,but on the whole,the average annual rainfall of RCP45 scenario is larger than that of RCP85 scenario.In the future,the temperature of the basin will show a trend of fluctuating increase,with the increase rate of 0.2?/10a under RCP45 scenario and 0.6?/10a under RCP85 scenario.The temperature change trend of RCP45 scenario will change dramatically around 2040s,and then the warming rate of RCP45scenario will be flat,while the warming rate of RCP85 scenario will continue to increase.On the whole,the average annual temperature of RCP85 was higher than that of RCP45.(2)The characteristics of land use change in the upper reaches of sansha River basin are as follows:in terms of spatial distribution,the main land use types in the basin are woodland(1200.45km~2),grassland(1116.84km~2)and cultivated land(840.30km~2),and the areas of towns,villages and water bodies are small,which are 10.69 km2,5.97 km2 and0.98 km2 respectively.In terms of time change,the change of land use area in the basin is not obvious,which is mainly manifested as the increase and decrease of scattered,which may be caused by the limitation of karst mountain environment,and large-scale land use development is difficult.The overall transfer rate of cultivated land was 1.5 times that of forest land and 1.3 times that of grassland,while the rate of urban growth was more than 24 times,indicating that the development and construction of human activity land in this period was fast.The change rates of forestland and grassland are similar,which may be related to the implementation of ecological policy.Among the land use types in the basin in 2035,the area of forest land is the largest(1197 km~2),followed by grassland(1127 km~2).The area of cultivated land changes greatly,increasing to 966 km~2,and the area of towns and villages is almost unchanged.Due to the limitations of terrain and traffic lines,the future land use changes are still not significant.In order to fine-evaluate the impact of land use on runoff,the forestland to grassland scenario and the grassland to forest scenario were set up respectively,and the area of other land types remained unchanged.In both extreme scenarios,the area of forestland and grassland was 2310 km~2.(3)The runoff in the upper reaches of Sancha River basin fluctuates at a rate of 2.8m3/s/10a and fluctuates between 17.61-63.03m3/s during the historical period.During 1980-1990,the runoff first increased and then decreased,and the change of runoff from 1991 to 2006 was dominated by positive anomaly,while from 2007 to 2017 was dominated by negative anomaly,indicating that the watershed water volume experienced large fluctuation in the periods of high water and low water.The overall variation trend of runoff is similar to that of rainfall,and the correlation coefficient with rainfall is 0.87,while that with air temperature is-0.35,indicating that air temperature has a small impact on the fluctuation of runoff,resulting in inconsistent response of runoff to rainfall,and runoff may also be affected by human activities.The main reason may be land use change.Quantitative analysis shows that the climate change and land use change in historical period are 92.6%and 6.38%in T1 period,46.2%and 46.89%in T2 period respectively.It indicates that during T1 to T2 period,the increase of human activity intensity has greatly changed the fluctuation of runoff,which is mainly manifested as the increase of forest and grassland area leads to the increase of surface roughness and the change of surface runoff.In the future period,the change trend of runoff under different scenarios is similar to that of rainfall,showing an overall upward trend.The growth rate of RCP45 and RCP85 scenarios is 0.9 m3/s/10a and 0.8 m3/s/10a respectively.The average annual rainfall of RCP45 is larger than that of RCP85 scenario,and rainfall is still the dominant factor of future runoff change.However,due to the influence of temperature,the fluctuation is large,indicating the existence of extreme rainfall events in the future.Under different land use scenarios,the mean runoff of extreme land use scenarios is lower than that of normal simulated land use scenarios,indicating that appropriate forest and grassland area and moderate increase of cultivated land area are conducive to surface runoff and increase watershed water yield.Extreme land use types completely change the roughness of the underlying surface of the watershed,resulting in a large loss of surface runoff,and the interception amount of forest is greater than that of grassland.Illustrate the basin in the future land use in the development process,through artificial regulation,a modest increase in cultivated land,woodland and grassland area of change is constant within a range,the increase of the maximum basin water rate,is advantageous for the downstream related areas and basin water resources development and utilization,meet the demand of water in these areas,establishing reasonable development and utilization of water resources policy in the future.