Effects Of Land Use Change On Land Surface Energy Balance In The Yellow River Basin

With the social changes and economic development,human activities will inevitably lead to the change of land surface conditions,and the change of land surface conditions can not only produce regional impacts,but also produce larger scale or even global impacts through the processes of biogeochemical and biogeochemical cycles.Land use and land cover change(LUCC)can directly affect the absorption and energy consumption of surface radiation by changing the physical characteristics of the surface,such as surface albedo,roughness and evapotranspiration,thus causing the change of surface energy balance and surface temperature,and then affecting the regional climate.The surface energy budget is the link between land and atmosphere energy conversion,and it is an important intermediate mechanism of LUCC-induced temperature change.The interaction between land and atmosphere is mainly realized through the change of surface heat and radiation balance,and the response of land surface system to climate change is also transmitted through the process of surface heat and radiation balance.At present,the changes of land use and land cover and their impacts have become a hot issue in global change research.Therefore,it is of great social significance to scientifically evaluate and predict the impact of land use change on climate,and provide decision-making basis,decision-making theory and decision-making suggestions for government agencies.Based on the surface energy balance algorithm,this paper uses ARCGIS spatial statistics and other methods to extract the energy parameters of different land types,and uses the remote sensing data of medium resolution imaging spectrometer and the surface energy balance algorithm to quantify the changes of surface energy budget corresponding to land use changes in the Yellow River Basin from 2000 to 2015.Net radiation(R_n)and latent heat flux(LE)are used to represent the energy intake and expenditure on the surface,respectively,and the difference between them(LE-R_n)represents the warming or cooling effect.The types of land use change in the Yellow River Basin are divided into five categories:old urban area(OU),urban expansion area(UE),natural and semi-natural area(PP),cropland(CP)and mixed area(MA).Using MODIS remote sensing data and surface energy balance algorithm,the climate change caused by bio-geophysical effects in the Yellow River Basin from 2000 to 2015 is analyzed,and four typical prefecture-level cities in the Yellow River Basin are discussed.The results show that:(1)The total net radiation(R_n)and latent heat flux(LE)of the Yellow River Basin increased from 2000 to 2015,and the high-value areas were located in urban expansion areas and natural and semi-natural areas,among which the areas greatly affected by human activities had higher net radiation value and lower latent heat flux,while the natural areas such as water or woodland and grassland had higher latent heat flux and lower net radiation,that is,water or woodland cover.(2)Both net radiation and latent heat flux showed an upward trend,but the upward trend of net radiation was more obvious than that of latent heat flux,and increased with the increase of human influence intensity,indicating that human activities strengthened the positive trend of surface energy intake and promoted the warming effect.(3)From 2000 to 2015,the difference of latent heat flux and net radiation(LE-R_n)in the Yellow River Basin showed a downward trend,with a multi-year trend value of-1.64 W/(m~2·year),which indicated that the feedback effect of land use change on regional warming was enhanced,and with the increase of human activities,the LE-R_n value of corresponding land types was decreasing,and regional warming was more obvious.(4)Under five land types,net radiation has a greater impact on energy budget than latent heat flux,and in land types with greater human influence,the surface temperature is more sensitive to net radiation changes,which indicates that in areas with intensive human activities,the adjustment of R_n to LST can be used to improve the urban thermal environment.(5)For four typical cities in the Yellow River Basin,there are differences in the adjustment factors of surface temperature.In Jinan and Zhengzhou,the net radiation has obvious effect on the surface temperature,while in Lanzhou and Xining,the latent heat flux has obvious effect on the surface temperature.This study emphasizes the difference of energy budget of different land use types under the influence of human activities,discusses the bio-earth effect of the whole Yellow River Basin and local cities in LUCC,and analyzes the climate warming or cooling effect along the Yellow River Basin according to the energy intake caused by surface albedo and the energy expenditure caused by latent heat flux,which provides a theoretical basis for judging the climate change trend of the Yellow River Basin from the perspective of bio-geophysics and analyzing the related factors affecting the urban thermal environment.