| Mass elevation effect refers to the warming effect caused by mountain or plateau uplift.The mass elevation effect changes the heat distribution pattern of the mountain and its surroundings,resulting in the temperature inside the mountain is higher than the same altitude area outside the mountain,so that the distribution of the boundary of the mountain vertical zone inside the mountain is higher than that outside the mountain.The quantification of mass elevation effect is an important factor to explain the distribution of mountain vertical zone.However,at present,the research on mass elevation effect mostly focuses on the influence of mountain terrain factors on the temperature field and the distribution boundary of mountain vertical zone.There is a lack of research on the relationship between key surface parameters related to ground air energy exchange and mass elevation effect,which leads to the quantification of mass elevation effect and can not reflect the formation mechanism of mountain effect.Qinling-Daba Mountains is the North-South dividing line of China,and the distribution of mountain vertical zone is extremely complex.The quantitative study of mass elevation effect based on key surface parameters is helpful to explain the complex distribution of mountain vertical zone in China’s north-south transition zone from the mechanism and determine the specific location of warm temperate zone and north subtropical Zone in China.Based on the surface albedo,evapotranspiration,land cover type,normalized vegetation index and normalized water index of MODIS,as well as the slope,aspect,latitude and base level height calculated by DEM data,combined with the surface temperature data at the same altitude of Qinling-Daba Mountains,this paper uses the random forest method,The main controlling factors of mass elevation effect in Qinling-Daba Mountains and four typical areas in Qinling-Daba Mountains(Funiu Mountain,Taibai Mountain,Shennongjia mountain,Dieshan mountain and their surrounding areas)are analyzed;Then,DEM data is used to extract the grid data sets of 1500m,2000m,2500m,3000m and 3500m altitude in Qinba Mountains.Combined with MODIS surface temperature data,based on random forest model and key surface parameters of each region,the surface temperature at the same altitude in the blank area is reconstructed,and the size,distribution and change of mass elevation effect at 1500m,2000m,2500m,3000m and 3500m are analyzed;The size,distribution and variation of mass elevation effect under the average altitude of four typical areas.The main results and conclusions are as follows:(1)Qinling-Daba Mountains and its four typical areas(Funiu Mountain,Taibai Mountain,Shennongjia mountain and Dieshan mountain)have great differences in temperature at the same altitude,but there is a strong correlation with the selected nine indicators(surface albedo,evapotranspiration,land cover type,normalized vegetation index,normalized water index,slope,aspect,latitude and mountain base elevation),and the R~2 between them is 0.62-0.81(P<0.01).There are obvious differences in the factors affecting the change of surface temperature at the same altitude in Qinling-Daba Mountains and its different regions.Latitude,surface albedo and,mountain base height and evapotranspiration have an important impact on the mountain effect and surface temperature at the same altitude in different regions.(2)Qinling-Daba Mountains and its four typical areas(Funiu Mountain,Taibai Mountain,Shennongjia mountain and Dieshan mountain)have great differences in the key surface parameters affecting the surface temperature at the same altitude.The four factors that have the greatest impact on the surface temperature at the same altitude in Qinling-Daba Mountains are latitude,slope direction,evapotranspiration and slope.The VI values of the multi factor random forest model reach 1.72,1.20,1.13and 1.12 respectively.The four factors that have the greatest impact on the surface temperature at the same altitude in Funiu Mountain and its surrounding areas are base level height,surface albedo,latitude and evapotranspiration.The VI values of the multi factor random forest model reach 0.78,0.75,0.73 and 0.57respectively.The four factors that have the greatest impact on the surface temperature at the same altitude in Shennongjia and its surrounding areas are evapotranspiration,latitude,base level height and land cover type.The VI values of the multi factor random forest model reach 0.88,0.80,0.78 and 0.75 respectively.The four factors that have the greatest impact on the surface temperature at the same altitude in Taibai Mountain and its surrounding areas are surface albedo,evapotranspiration,latitude and normalized water index.The VI values of the multi factor random forest model reach 0.68,0.62,0.54 and 0.53 respectively.In Dieshan and its surrounding areas,the four factors that have the greatest impact on the surface temperature at the same altitude are normalized vegetation index,evapotranspiration,surface albedo and latitude.The VI values of the multi factor random forest model reach 0.50,0.49,0.30 and 0.28respectively.(3)Based on the random forest model and key surface parameters of each region,the surface temperature at the same altitude of 1500m,2000m,2500m,3000m and 3500m in typical areas is reconstructed,and the spatial pattern of mountain effect is analyzed.From west to East,the mass elevation effect changes upward.At the latitude line of 32.66°N,the mass elevation effect decreases first and then increases from west to East.The mass elevation effect reaches the maximum in Xuebaoding area,which are 7.94℃,9.46℃,9.05℃,9.86℃and 7.89℃respectively;Along the 33.96°N latitude line,the altitude mass elevation effect increases after decreasing step by step from west to East.The mass elevation effect at1500m and 2000m reaches the maximum in the area between Dieshan and Xiangshan,which are 8.65℃and 9.71℃respectively.The mass elevation effect at 2500m and 3000m reaches the maximum in Dieshan,which are 13.76℃and 12.12℃respectively.The mass elevation effect at 3500m reaches the maximum in Xiangshan area,which is 7.72℃.At 1500m,2000m and 2500m altitude,the lowest mass elevation effect is located in the north slope of Qinling Mountains,and the largest is in the West Qinling Mountains,which are 0.83℃,1.36℃and 1.76℃respectively;At 3000m altitude,the minimum mass elevation effect is located on the north slope of Daba Mountain and the maximum is located in the West Qinling Mountains,which is 1.26℃;At an altitude of 3500m,the minimum mass elevation effect is located on the south slope of Daba Mountain,and the maximum is located in the West Qinling Mountains,which is 0.68℃.At all altitudes,the mass elevation effect of the West Qinling Mountains reaches the maximum.(4)Spatial variation of mass elevation effect in typical areas.The mass elevation effect of Funiu Mountain and its surrounding areas decreases from east to west;From south to north,it shows a trend of decreasing first and then increasing.The mass elevation effect in this area is the largest,reaching 8.83℃.The mass elevation effect of Taibai Mountain and its surrounding areas decreases step by step from east to west;From south to north,it shows a trend of first decreasing and then increasing,and the mass elevation effect in this area is the largest,reaching 7.65℃.The mass elevation effect in Shennongjia and its surrounding areas decreases first and then increases from southwest to northeast.The mass elevation effect in the southwest is higher than that in the northeast,and the maximum mass elevation effect in this area is9.60℃.The mass elevation effect of Dieshan and its surrounding areas increases from east to west;From south to north,it shows a trend of decreasing first and then increasing.The mass elevation effect in this area is the largest,reaching 12.58℃. |
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