| China’s urbanization has entered a rapid development stage,with the continuous expansion of urban economy and population,as well as the expansion of urban spatial scope and land area.The rapid three-dimensional expansion of cities has led to an increasing proportion of construction land occupation,a decline in the proportion of urban green space,and an increase in urban carbon emissions due to the increase in urban population size.This will inevitably lead to a series of problems.It is of great significance to study urban carbon emissions and green space carbon absorption in the context of three-dimensional urban expansion,not only providing reference for the formulation of future urban planning,but also providing data reference and theoretical support for achieving the carbon neutral goal in China.This study selected Zhengzhou as the research area,based on the Globeland 30 global surface cover data and building height data,analyzed the land use pattern and three-dimensional spatial characteristics of buildings in Zhengzhou in 2020,predicted and simulated the three-dimensional expansion of Zhengzhou in 2040based on the land use model and random forest prediction model,and explored the spatial factors of land use conversion and three-dimensional expansion in Zhengzhou,And combined with the nighttime lighting data of Zhengzhou in 2020,the carbon emissions of residential areas and the three-dimensional volume of the city were inverted to predict the carbon emissions of residential areas in 2040.At the same time,based on the predicted green area,the carbon absorption of green spaces in Zhengzhou in 2040 was predicted,and the carbon balance of residential carbon emissions and green space carbon absorption in Zhengzhou was analyzed for the current and 20 years to come.The main conclusions are as follows:(1)In 2020,construction land in Zhengzhou is mainly distributed in the middle region of the northern part of Zhengzhou,urban green space is mainly distributed in the western and southwestern regions of Zhengzhou,cultivated land is mainly distributed in the eastern region of Zhengzhou,and wetlands and water bodies are distributed in the northern region of Zhengzhou.From 2000 to 2020,the urban green space area,construction land area,and wetland area showed an overall trend of increase,while cultivated land and water body showed a downward trend.This study validated the simulated land use pattern with the actual land use pattern.The accuracy analysis showed that the Kappa coefficients were0.78 and the FOM were 0.23,respectively,indicating that the simulation accuracy of the PLUS model was considerable and the simulation effect was good.Using the PLUS model to analyze the relationship between various land changes and various driving factors,the results show that urban green space changes mainly occur in areas far away from high population density,construction land grows around areas with more nighttime lighting,cultivated land changes mainly occur in areas with lower elevations,and wetlands change partially away from areas with more nighttime lighting,and changes mainly occur near water bodies.Using Markov chain to predict the land use of Zhengzhou in 2040,it was found that only the area of construction land showed a significant upward trend in 2040,while the area of other land types decreased.(2)The average floor area ratio of the central urban area of Zhengzhou is relatively large,while the average floor area ratio of most administrative districts outside the central urban area is relatively small.The administrative district with the highest average floor area ratio is Jinshui District,which is 7.44,the smallest administrative district is Dengfeng District,which is 3.69,and the administrative district with the highest average floor area ratio is 2.02 times the smallest administrative district.Based on the constant average plot ratio of each administrative district in Zhengzhou and the predicted area of construction land in 2040,the three-dimensional volume of each administrative district in 2040 is calculated.The results show that in 2040,Xinmi District,Dengfeng District,Xingyang District,Zhongmu District,and Xinzheng District had the largest growth rates of three-dimensional volume in various administrative regions of Zhengzhou,with increases of 94.72%,92.39%,63.55%,58.55%,and 56.00%,respectively;The smaller growth rates of volume were 39.78%,36.95%,24.03%,and 19.44%in Huiji District,Erqi District,Zhongyuan District,and Guancheng District,respectively;The smallest growth rate of volume is in Jinshui District,which is 15.61%.In the next 20 years,the three-dimensional volume of non-central urban areas in Zhengzhou will grow rapidly,while the three-dimensional volume of central urban areas will grow slowly.The rapid three-dimensional expansion of non-central urban areas in Zhengzhou indicates that Zhengzhou will further develop outward.(3)In 2020,the number of buildings in the entire city of Zhengzhou is concentrated in the central urban area,where buildings account for more than 80%of the total number of buildings,and the height of buildings is relatively high.In this paper,the trained random forest prediction model is used to predict the building height in 2020,and the predicted building height is compared with the real building height data in2020.It is concluded that the model R~2 is 0.84,indicating that the regression fit of the model is high.Using a random forest model to evaluate the importance of the impact of various spatial factors on building height,it was found that nighttime lighting was the biggest factor affecting the importance of building height,while the distance from the railway had the smallest impact on the importance of building height.Based on the current economic development,the height of buildings in Zhengzhou in 2040 was predicted,and the height of buildings predicted by the random forest was modified based on the three-dimensional volume in2040.The results showed that among the newly added buildings,the proportion of medium and high-rise buildings distributed in Zhongyuan District,Jinshui District,and Erqi District was relatively large,while the proportion of multi-storey buildings distributed in Zhongmu District,Xinmi District,Huiji District,Gongyi District,and Guancheng District was relatively large,while the proportion of multi-storey buildings distributed in Xingyang District.The proportion of low-rise buildings distributed in Shangjie District and Dengfeng District is relatively large,and Dengfeng District has a large number of single-storey buildings.(4)The carbon coefficient value per unit volume of buildings is roughly inversely proportional to the height of the building.As the height of the building increases,the carbon coefficient value per unit volume of the building gradually decreases.At the same time,it is found that the carbon coefficient value per unit volume of buildings of different heights shows an overall downward trend from the central urban area to the non central urban area.In 2020,the carbon balance values of residential carbon emissions and green space carbon absorption in Zhengzhou were below zero,indicating that the carbon absorption of green spaces in various administrative regions of Zhengzhou was less than the carbon emissions.The entire urban green space in Zhengzhou could only absorb 2.72%of residential carbon emissions,and the carbon balance value of residential carbon emissions and green space carbon absorption was-9291400 tons,The carbon balance values of residential carbon emissions and green space carbon absorption in Shangjie District,where residents have the highest carbon balance values,are 16 times higher than those in Zhongmu County,where residents have the lowest carbon balance values of residential carbon emissions and green space carbon absorption.In 2040,the urban green spaces in the entire city of Zhengzhou could only absorb 1.79%of the residential carbon emissions,with a carbon balance value of-1395800 tons.The carbon balance values of Shangjie District,which had the highest residential carbon emissions and green space carbon absorption,and Zhongmou County,which had the lowest residential carbon emissions and green space carbon absorption,differed by 20.07 times.It indicates that there are significant differences in the carbon balance values of residential carbon emissions and green space carbon absorption between administrative regions in 2020 and 2040.Compared with 2020,the carbon balance value of residential carbon emissions and green space carbon absorption in Zhengzhou decreased by 4.6668 million tons in 2040,and the low-carbon level decreased by 50.23%.From 2020 to 2040,the overall ratio of carbon absorption to carbon emissions in Zhengzhou decreased by 0.93%on the basis of 2.72%.In the future,the amount of carbon emissions that urban green space can absorb will be reduced. |
PDF Full Text Request