| Land space is a bearing form of human—land system with land use as the core.Land use change is influenced by both natural processes and human activities,and it is one of the main factors that lead to the change of carbon cycle in terrestrial ecosystem.Based on the background of"two—carbon"strategy,this paper explores the relationship between land use and cover change of urban agglomeration and the temporal and spatial changes of ecosystem carbon stocks,in order to provide certain references for the regional carbon balance,territorial spatial planning and sustainable development of the ecological system of urban agglomeration.Taking Chengdu—Chongqing urban agglomeration as an example,multi—period land use data were selected and related driving factors were determined.Based on the PLUS—InVEST model,the land use spatial pattern of the Chengdu—Chongqing urban agglomeration in 2030 was simulated and predicted respectively under the two scenarios of natural development and ecological protection on the basis of clarifying the law of land use cover change during 2000—2020.The carbon storage and its temporal and spatial dynamic changes under the two scenarios were evaluated.The main research results are as follows:(1)Analysis of spatial—temporal changes of land use in Chengdu—Chongqing urban Agglomeration:From 2000 to 2010,the land use type area of Chengdu—Chongqing urban agglomeration has undergone great changes,and the changes of construction land and grassland area are the most drastic.With the rapid progress of urbanization,the blind expansion of construction land has become the general trend of this period,while the grassland area has rapidly decreased.From 2010 to 2020,the land types with the biggest changes in the area of Chengdu—Chongqing urban agglomeration are cultivated land and construction land,among which the construction land continues to expand and the growth area is more than that of the previous decade.In the past 20 years,construction land fluctuated greatly,and its dynamic value K was 7.14%,while the K value of other land types was not outstanding.Compared with the previous stage,the dynamic attitude of comprehensive land use showed a downward trend in the latter stage,which was in line with the law of land area change.From the perspective of 2000—2020,the circulation of various types of land shows significant characteristic changes.The transferred area of cultivated land was the largest,with a total of 12414.13 km~2,and the transferred area of forest land was the largest,with a total of 9107.21 km~2.From the overall direction of movement in the past 20years,the center of gravity of cultivated land and forest land moved to the northeast,grassland and unused land moved to the northwest,and water and construction land moved to the southeast.(2)Simulation and Prediction of land Use in Chengdu—Chongqing Urban Agglomeration:Combined with the actual situation of the study area,a total of 15 driving factors were selected from the aspects of natural environment,social economy and traffic location,etc.Combined with the random forest sampling model analysis,the RF test values of the six land classes were respectively 0.1689,0.1614,0.1023,0.0653,0.0924 and 0.0167.This provides effective data support for simulation research.Kappa coefficient and FOM coefficient were used to verify the accuracy of the 2020 simulation results and the land use types of Chengdu—Chongqing urban agglomeration,and the results were 0.817 and 0.052,respectively,indicating a good accuracy of the simulation results.In addition,in the simulation prediction expansion probability,the contribution of DEM is far ahead,up to more than 16%,and the contribution of other factors shows a trend of uniform decline.According to the land use distribution pattern of Chengdu—Chongqing urban agglomeration from 2000 to 2020,two typical scenarios of natural development and ecological protection were set up to simulate the land use evolution pattern of Chengdu—Chongqing urban agglomeration in 2030.Under the natural development scenario,the area of construction land increased the most,which was 1,906 km~2,while the other land types all decreased to varying degrees.Under the ecological protection scenario,except the construction land,the area of woodland and grassland increased by 101 km~2 and 345 km~2,respectively.It embodies the effectiveness and necessity of ecological protection.(3)Analysis of Land use Change and carbon storage evolution in Chengdu—Chongqing Urban Agglomeration:The total carbon reserves of Chengdu—Chongqing urban agglomeration in 2000,2010 and 2020 are 5648.610×10~6t,5669.267×10~6t and 5673.100×10~6t,respectively,by substituting the land use data and regional carbon density of the agglomeration in the InVEST model during 2000—2020.From the perspective of spatial distribution,the carbon storage of the northwest area with Chengdu as the core is much higher than that of the southeast area with Chongqing as the core.The total carbon storage of the northwest area with Chengdu as the core is 4269.539×10~6t,4273.883×10~6t and4269.443×10~6t in 2000,2010 and 2020,respectively.In the southeast region with Chongqing as the core,the total carbon storage values were 1372.354×10~6t,1386.904×10~6t and 1395.076×10~6t,respectively,showing a trend of continuous growth.From the change of carbon storage of different land types,the carbon storage of cultivated land and grassland decreased by 77.732×10~6t and 62.160×10~6t,respectively,while the carbon storage of forest land,water area,construction land and unused land increased by 60.457×10~6t,10.321×10~6t,90.443×10~6t and 3.159×10~6t.Under the natural development scenario,the total carbon storage of Chengdu—Chongqing urban agglomeration is predicted to reach5623.099×10~6t in 2030,a decrease of 50.001×10~6t compared with that in 2020,while under the ecological protection scenario,the average annual decrease is 4.9753×10~6t,with a small reduction in carbon storage.According to the results of carbon storage changes during land class conversion,from 2000 to 2020,the carbon storage of Chengdu—Chongqing urban agglomeration decreased by 25.447×10~6t due to the transformation of single land type to multiple land types,mainly due to the quantitative conversion of cultivated land,forest land and grassland to construction land.Compared with the previous two decades,the carbon reserves of Chengdu—Chongqing urban agglomeration in 2030decreased by 2.955×10~6t under the natural development scenario,while significantly increased by 393.057×10~6t under the ecological protection scenario.Comparing the two typical development scenarios,the carbon storage of urban agglomerations under ecological protection measures that restrict the transfer of forest land and grassland to other land types tends to be more stable,avoiding a rapid decline. |
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