Land Use Change And Its Impact On Carbon Storage Under The Constraints Of “Three Lines”

The increase of CO₂ content in the atmosphere is an environmental issue of global concern.How to reduce CO₂ emissions and improve carbon sequestration capacity has become a difficult research point.Terrestrial ecosystems play a key role in absorbing CO₂and regulating climate change due to the large number of carbon sequestration units distributed on the surface.Increasing carbon storage in terrestrial ecosystems can effectively reduce CO₂ content and is one of the most economical,feasible and environmentally friendly ways to mitigate the greenhouse effect.Land use change can directly affect the carbon storage of terrestrial ecosystems by causing changes in the structure and function of terrestrial ecosystems,which is the second largest cause of CO₂surge.The ecological protection-permanent basic farmland-urban development boundary red line（referred to as the"three lines"）is the core of national land planning,which can better restrict land use and thus affect carbon storage.In this paper,under the background of the"double carbon"goal and the continuous advancement of national land space planning,Arc GIS technology is used to analyze the characteristics of land use change in Wuhan City Circle,and the In VEST model is used to measure and study the temporal and spatial evolution of carbon storage.On this basis,a"three-line"constraints scenario was designed and compared with the natural development scenario.The Markov-FLUS model was used to simulate the land use change of Wuhan City Circle under different scenarios,and its impact on carbon storage was compared and analyzed.The main research conclusions are as follows:（1）The characteristics of land use change in Wuhan City Circle:In terms of time,cultivated land,forest land,grassland and unused land decreased by 1291.68km²,169.665km²,33.452km² and 43.589km² respectively,while construction land and water area increased by 1192.093km² and 346.293km² respectively.The area of cultivated land transferred out is the largest,reaching 1360.5462km²,of which the area turned to construction land is as high as 937.2024km²,and the area of water turned to water is397.683km²,indicating a high dynamic degree of comprehensive land use.From a spatial point of view,the area of cultivated land reduction is almost all over the study area,with Wuhan（386.67km²）and Xiaogan（182.73km²）reducing the area the most.During the study period,the construction land showed a huge growth trend,covering the whole study area,and many It is the area of original cultivated land,forest land and water area.（2）The temporal and spatial evolution of carbon storage in Wuhan City Circle:In terms of time,the carbon storage in Wuhan City Circle in 2000,2005,2010,2015 and2020 was 683.12Tg,680.98Tg,679.74Tg,674.83Tg and 673.886Tg,respectively.The density is 117.89t/hm²,117.52t/hm²,117.31t/hm²,116.46t/hm² and 116.3t/hm² respectively.Among them,Huanggang,Xianning and Xiaogan are the three cities with the largest carbon storage in the City Circle.In 2020,the sum of the three carbon storage accounts for about67.36%of the region,and they are important carbon pools in the region.From a spatial point of view,the carbon storage of all cities in the Wuhan City Circle has decreased,of which Wuhan has the largest reduction in carbon storage,which is 2.74Tg,accounting for29.68%of the total reduction.The carbon density reduction area mainly presents a circle around the main urban area.Layered spread.Followed by Huanggang（1.73Tg）,Xiaogan（1.35Tg）,and Xianning（1.47Tg）,the carbon density reduction areas in these three cities are distributed in a point-like manner,most of which are concentrated around the original construction land.（3）The characteristics of land use change under the constraints of"three lines"in Wuhan City Circle:The area of cultivated land reduction（524.898km²）under the“three-line”constraints scenario is much smaller than that of the natural development scenario（950.493km²）,and the forest land has also increased（118.047km²）.Although the area of construction land has increased in both scenarios,in the natural development scenario,the expansion is more disorderly,and cities spread disorderly on the basis of their original construction land.However,under the“three-line”constraints scenario,the increased area of construction land（391.419km²）is not only much smaller than the natural development scenario（1075.943km²）,but also more inclined to intensive use,and the newly added construction land is guided to gather within the red line of the urban development boundary.（4）Influence characteristics of land use change on carbon storage under the constraints of"three lines"in Wuhan City Circle:The conversion of cultivated land to construction land under the natural development scenario is the main reason for the sharp reduction of carbon storage.Under the"three-line"constraints scenario,the area of cultivated land turned to construction land is greatly reduced,and the carbon sequestration of forest land due to the conversion of other land types reaches 2.009Tg.At the same time,the transformation of land types under the natural development scenario will lead to a loss of carbon sink economic value of US$134.9012 million in Wuhan City Circle,while it is US$62.3164 million under the“third-line”constraints scenario.The land use intensity and carbon storage of the two scenarios are significantly negatively correlated at the 0.01 level,and the carbon storage in the lower intensity zone is the highest,but the average carbon storage of each grade of land use intensity under the“three-line”constraints scenario is higher than natural development scenarios.