Response Of Runoff To Land Use And Climate Change In The Middle And Upper Jinshajiang River Basin

Land use and climate change will increase the instability and imbalance of the hydrological cycle in the basin,affect the total amount,spatial and temporal distribution and composition of water resources in the basin,and then bring great challenges to the water security of the basin.Therefore,it is necessary to study the response of runoff to land use and climate change to enhance water security in the basin,which has become a research hotspot in the field of water science development in recent years.The middle and upper reaches of the Jinshajiang River are important hydropower energy bases and industrial and agricultural production bases in China.The water security situation in this region is closely related to social and economic development,which is of great significance for the realization of China’s“carbon peak”’and“carbon neutrality”goals.Therefore,this paper takes the middle and upper reaches of Jinsha River as the research area,and uses linear regression test,Mann-Kendall Trend Method(MK),cumulative anomaly method and Pearson correlation coefficient method to identify the historical trend and mutation characteristics of hydrometeorological elements.The historical change characteristics of land use change were analyzed by using transfer matrix and dynamic degree analysis method.Based on the Coupled Model Intercomparison Project Phase 6(CMIP6)and the Celluar Automata(CA-Markov)model,the future climate and land use were simulated.On this basis,the Soil and Water Assessment Tool(SWAT)model suitable for the study area was constructed.84 scenarios were set up to study the response of runoff to land use and climate change.The results show that:(1)The application of SWAT model in the study area has good applicability.The SWAT model of the middle and upper reaches of the Jinshajiang River was constructed and the runoff was simulated.The R~2 and NSE of each hydrological station were above 0.8 during the calibration and validation periods,indicating that the SWAT model had good applicability in the study area.(2)The characteristics of climate and land use change in historical period were clarified.From 1973 to 2020,precipitation,temperature and evapotranspiration increased significantly,while runoff did not increase significantly.The increase of summer precipitation,evapotranspiration and runoff plays a leading role in the increase of annual precipitation,evapotranspiration and runoff,and the increase of winter temperature plays a leading role in the increase of annual temperature.In the past 40 years,except for the decrease of unused land area,the area of other land types has increased,and the land use change in 2015-2020is the most dramatic.(3)The future climate change under the“double carbon”and“high carbon”paths and the future land use based on CA-Markov model are predicted.From 2021 to 2060,the study area showed an obvious warm and humid trend,and the temperature and precipitation increased significantly.And the temperature and precipitation under the“high carbon”path increased more.The future land use change continues the trend of historical land use change,which shows that the area of other types of land increases except for the decrease of unused land area.(4)The response of runoff to land use change was explored.From 1973 to 2020,the decrease of unused land and the increase of forest land,grassland and cultivated land area led to the decrease of runoff.The order of contribution rate of grassland,woodland,cultivated land and unused land to runoff reduction is:woodland>grassland>cultivated land>unused land.The runoff showed a decreasing trend under the future land use change scenario,which was due to the significant reduction of unused land and the increase of forest land,grassland and cultivated land.Under the rotation fallow scenario,the cultivated land has been efficiently utilized,resulting in a decrease in runoff.The measures of contour tillage,strip tillage and mulching tillage were carried out in the study area,which effectively alleviated soil erosion and reduced runoff.(5)The response of runoff to climate change was clarified.The response rate of runoff to temperature is-4.31%/°C.The response rate of runoff to precipitation was+19.89%/10%.The future average annual runoff in the study area under the SSP1-2.6 and SSP2-4.5 paths is higher than that in the historical period,and the future average annual runoff in the study area under the SSP3-7.0 and SSP5-8.5 paths is lower than that in the historical period.The runoff in the middle of the study area under all paths in the future period is higher than that in the historical period,which indicates that the water resources in the middle of the study area will be more abundant in the future.(6)The future runoff in the study area under“double carbon”and“high carbon”scenarios was simulated.Under the“double carbon”scenario,the average annual runoff in the future period of the study area is higher than that in the historical period,and the average annual runoff in the medium term is higher than that in the near future.Under the“high carbon”scenario,the average annual runoff in the future period of the study area is lower than that in the historical period,and the average annual runoff in the medium term is lower than that in the near future.From the perspective of monthly average runoff,water resources are more abundant and more evenly distributed within the year under the“double carbon”scenario.(7)The contribution of climate change and land use change to runoff was quantified.The contribution rate of climate change to runoff change in the study area is 95.06%,and the contribution rate of land use to runoff change is 4.96%.(8)To address water security problems in the region,the study recommends optimizing water resource allocation in the basin,improving the capacity for flood and drought control,implementing different cultivation measures for arable land,and converting unused land in the basin into forest and grassland.