Study On The Impact Of Land Cover Change On Urban Heat Island In Hohhot

With the continuous progress of urbanization,the urban heat island effect has become increasingly prominent.Studying the impact of land cover on urban heat island and exploring the quantitative relationship between urban green space and heat island effect can provide a scientific basis for urban forest management and land spatial planning and layout.Hohhot is a typical city in arid and semi-arid areas.It is not only an important node of the ecological security barrier in the northern part of the motherland,but also plays an important role in the urban agglomeration of Hohhot,Baotou,Erdos and Yulin,which is vigorously cultivated and developed in the 14th Five-Year Plan.In the process of urbanization,the construction of urban green space ecosystem will become an important direction of forest management.This thesis takes Hohhot as the research object.Based on the theory of remote sensing and GIS spatial analysis,the characteristics of climate factors such as air temperature,surface temperature and land cover change were studied by using the methods of landscape pattern index and heat island distribution index,and the three-dimensional green quantity was measured by sampling,and the regression model of three-dimensional green quantity was constructed by combining vegetation index,and the correlation between it and surface temperature was established to analyze the impact of heat island effect.The main conclusions of the study are as follows:(1)In recent 30 years,the average temperature in Hohhot has been rising slowly in fluctuation.The Uhi intensity showed an upward trend and showed a banded distribution from north to south.The urban heat island effect is obvious,which is higher in winter than in summer,and higher at night than in daytime.The intensity of intra-day heat island is greatly affected by solar radiation,which decreases rapidly after sunrise and reaches the lowest level at 15:00-16:00,and increases rapidly after sunset.Peak at 21:00.(2)In the past 30 years,the area of construction land and forest land increased significantly,while the area of cultivated land,shrub and grassland decreased significantly,and the change of bare land and water body was not obvious.Forest land(including shrub)contributed the most to the intensity of heat island of type I and II,and its cooling effect decreased year by year.The contribution of construction land to the intensity of class IV and V heat island is the largest,and its warming effect is increasing year by year.The complexity of landscape patch shape increases,and tends to gather,and the degree of fragmentation increases.The correlation between landscape indices and land surface temperature was different at different scales.The AI,LPI and COHESION were significantly negatively correlated with land surface temperature at 0.01 level.Edge density(ED)is significantly positively correlated with surface temperature at the 0.01 level.The normalized difference vegetation index(NDVI)decreased significantly in the central urban area of the study area,but increased significantly in most of the other areas,and the normalized difference built-up index(NDBI)was on the contrary.The former is negatively correlated with the surface temperature,while the latter is positively correlated,and both of them pass the 0.01 level of significance.(3)In the central area of Hohhot,Willow,Hebei poplar,Acacia,Salix matsudana,Sophora japonica,Prunus triloba,clove,apricot,pearl plum and privet are the tree species with larger three-dimensional green quantity per tree.(4)The linear equation with CVI as the independent variable is suitable to be the parameter of the three-dimensional green quantity inversion model(R~2=0.72),and its regression model is VQ=-30.412+35.842×CVI.In 2018,the urban three-dimensional green quantity and its corresponding surface temperature in the built-up area have a large range of values,the maximum value of the three-dimensional green quantity per unit area is 32.9 m~3/m~2,and the minimum value is 0.01m~3/m~2;Maximum surface temperature:50.85?,minimum:23.85?.In the study area,the three-dimensional green biomass per unit area was mainly concentrated in the range of 0 m~3/m~2-15.78 m~3/m~2,accounting for85%of the total sample points.The regression model was LST=-0.554×VG+43.601,which was significantly correlated at the 0.01 level(one-sided).Combined with the regression model analysis of three-dimensional green quantity per unit area and surface temperature,it is concluded that when the three-dimensional green quantity per unit area increases by 0.1 m~3/m~2,the surface temperature decreases by 0.06?.(5)In the past 30 years,the three-dimensional green quantity per unit area of Daqingshan Mountains in the south,east and north of the built-up area of Hohhot has increased significantly,and the interior has increased with the construction of urban forests.The edge of the built-up area decreases with urban expansion.In 2018,the three-dimensional green volume per unit area of Manduhai Park,Qingcheng Park,Wulanfu Park and Arboretum was larger than 19.6m~3/m~2.The three-dimensional green quantity of shanty towns in the northwest of the built-up area,Xiaoheihe and Daheihe rivers and their surrounding plots,and individual residential areas with poor green environment in the urban area is relatively small,which needs to be increased urgently.