Impacts Of Land Use And Climate Change On Runoff Of The Upper Reaches Of The Minjiang River In The Past 40 Years

Since theconception of water security was brought up in the Stockholm Waterseminarin 2000,it has received an increasing attention of the world.As the water source of Chengdu Plain and Tianfu New District and the ecological barrier of the upstream of the Yangtze River,the upstream of the Minjiang River has received broad attention from public.More than 10 CPPCC(China People's Political Consultative Conference,CPCC)members at the Second Session of the 13th National Committee of the Chinese People's Political Consultative Conference propose a joint proposal of introduce the dadu river to replenish the mingjiang river.In the background of global warming and land use strongly changed,proper understanding of the evolvement rule and response mechanism of the upstream runoff on LUCC((Land Use and Land Cover Change,LUCC)and multi-temporal and spaced GCC(Global Climate Change,GCC)is an especially important essential work for correctly evaluating the risk of water security and coming up with reduction and adaptation measures,and provide scientific basis and technical support for water safety control and integrated river basin management in the upper reaches of the Minjiang River.This article takes the upstream Minjiang River as the research area,collects the Digital Elevation Model(DEM),land use,soil data,and meteorological data,and analyzes the land use change in the study area by the land use transfer matrix.The SWAT(Soil and Water Assessment Tool,SWAT)database and model in the upper reaches of the Minjiang River were constructed to simulate the hydrological process,and various scenarios were set up to analyze the runoff changes.Draw conclusions as follows:(1)To investigate the trend of land use changeby comparing the land use situation and land use transfer matrix of each year,it is found that the cultivated land and forest land in the upstream Minjiang River during the study periodshow a decreasing trend while the water area,construction land and unused land has increased significantly by occupying the area of cultivated land and woodland.(2)Through the statistical analysis of the daily data of five meteorological stations in theupsteam Minjiang River to explore the climate change trend,it is found that the temperature is increasing and the rainfall is decreasing.The daily maximum and minimum temperature changes are:+0.13°C/5a,+0.158°C/5a;change of rainfall capacity is-18.04mm/5a;The significant alteration time of the temperature and rainfall sequence from 1979-2014 in upstream mingjiang river is year 1995 by comprehensively employing MK test,sliding T test,cumulative anomaly method.(3)Byprocessing the basic data,the SWAT database of the study area is constructed.After finishing the construction of SWAT model,to divide the watershed into 31 sub-basins and 1369 Hydrologic Research Units(HRUs).(4)Harness monthly runoff monitoring data of multiple years from multiple hydrological stations to determine and verify.The calibration and validation period and validation period of the model evaluation index correlation coefficient R~2 and the Nash-Sutcliffe efficiency coefficient(NSE)rate at each site are are greater than 0.8,showing that the SWAT model has good applicability in the upstream of the Minjiang River.(5)By overlapping stimulation of land use data and meteorological data in different periods,it is found that the impact of climate change on runoff during the study period is greater than the impact of land use change,and the contribution rate of runoff change of climate change and land use change respectively are 57.55.%and42.45%.(6)Stimulating the runoff by setting situational pattern of climate change,the simulation results show that the simulated runoff is more than the original scenario under the reduced temperature,but the amount of runoff increases is less for every1°C decrease;the runoff simulated under the increased temperature is less than the original scenario,but the amount of runoff decreases is less for every 1°C increase,runoff is increasing;the increasing trend of runoff the increase and decrease of runoff is consistent with precipitation.The change of runoff caused by temperature rise is Songpan-Shaba section>Shaba-Taiping section>Taipingyu-Zipingpu section;the runoff change caused by rainfall change is Songpan-Shaba section>Taipingyu-Zipingpu section>Shaba-Taiping section.(7)The simulation result under the extremely situation of land use change shows thatthe contribution to the yielding runoff is arable land>grassland>forest land;under different farming patterns,crop residue tillage has the highest level of inhibition on runoff,reaching 2.4%.