| Effectively strengthening the governance of plateau lakes,establishing the idea of "river basin governance",and fighting the battle of "Lake Revolution" are one of the major measures taken by Yunnan Province to deeply implement the spirit of General Secretary Xi Jinping’s important speech on his inspection of Yunnan and strive to become the vanguard of China’s ecological civilization construction.Dianchi Lake is a famous plateau lake in western China.With the large-scale reclamation of the lake in the 1960 s and 1970 s and the rapid development of urbanization and industrialization since the reform and opening up,great changes have taken place in the land use/land cover situation in the Dianchi Lake basin.Accordingly,this has triggered a series of irrational land development and utilization issues,bringing increasing pressure to the ecological environment of the river basin,which directly affects the sustainability of the development of Dianchi Lake basin.It is urgent to carry out research on the rationality of land use change to promote the "win-win" of ecological environmental protection and sustainable economic and social development in the Dianchi Lake basin.This paper takes the Dianchi Lake basin as the research area and takes the vector data of land use/land cover classification from 1980 to 2020 as the basic data,calculates the quantitative structure of land use,land use transfer matrix,the center of gravity of each land use type and migration distance,and analyzes the characteristics of land use change in the Dianchi Lake basin in the past 40 years.On this basis,the field survey,geographic information system,evaluation and analysis model,qualitative and quantitative integration of a variety of technology and methods synthesis,the land use types changed during 1980-1990,1990-2000,2000-2010 and2010-2020 were used as evaluation units,introducing land suitability assessment,vegetation succession patterns,and relevant regulations and policies in the Dianchi Lake basin to establish criteria for assessing the rationality of land use change,the rationality of land use change in the Dianchi Lake basin in recent 40 years was quantitatively evaluated,and then the CA-Markov model was used to predict the land use change in the Dianchi Lake basin in 2030.The main findings are as follows:(1)From the perspective of land use changes from 1980 to 2020,the land type with the largest decrease in the basin was paddy fields,with a total decrease of 153.65km~2,and the land type with the largest increase was urban land,with a total increase of 248.04 km~2.The proportion of cultivated land decreased from 24.29% to 17.25%,and the proportion of construction land increased from 13.19% to 23.50%.The main destination of cultivated land,woodland,grassland and water area is construction land;Except for construction land,the increase area of other land types does not exceed 10km~2,and the increase is relatively small.Spatially,the distribution of construction land along the northern coast of Dianchi Lake and on both sides of the river entering the lake has become more and more dense,and gradually spread from north to east,and cultivated land has been encroached upon in large quantities.Except for low-cover grasslands,the center of gravity of all types of land has undergone a certain degree of migration,and the center of gravity of tidal flat and other forest land has a long migration distance.(2)From the perspective of the rationality of land use change from 1980 to 2020,a total of 325.75 km~2 of land in the Dianchi Lake Basin underwent land type changes,of which 233.76 km~2 of land change was rational,91.99 km~2 of irrational change,RD value(rational degree)was 71.76%,and the rational level was Ⅲ.In the four periods,the rational degree of land use change was 72.68%,72.92%,79.59% and 67.49%,respectively,and the rational level were all Ⅲ,and there was some room for improvement.From the perspective of various land types,the rational degree of cultivated land change was 74.41%,the change of 148.37 km~2 was rational,and the change of 51.02 km~2 was irrational,and the rational degree was Ⅲ.Among the cultivated land converted to forest land,grassland and water area,41.87% of the land is suitable for cultivated land,and there is a problem that the cultivated land should not be retreated.A total of 185.21 km~2 of cultivated land was converted into construction land,of which 96.00% was suitable for cultivated land.The rational degree of forest land change was 69.11%,the change of 33.52 km~2 was rational,and the change of 14.98 km~2 was irrational and the rational degree was Ⅲ.A total of 2.85km~2 of forest land has been converted into shrub land,open forest land,grassland and cultivated land,and there is a certain degree of ecological degradation and deforestation and reclamation problems.In the past 10 years,the irrational area of open forest land and other forest land converted into construction land has increased and decreased rationality,which deserves attention.The rational degree of grassland change was 77.11%,the change of 50.23 km~2 was rational,and the change of 14.91km~2 was irrational,and the rational degree was Ⅲ.The rational degree of water change was 3.07%,the change of 0.35 km~2 was rational,the change of 11.05 km~2 was irrational,the rationality level was Ⅵ,and a total of 6.17 km~2 of lakes were landfilled for development and construction,and the problem of "lake reclamation development" cannot be ignored.The rational degree of the change of construction land was 98.26%,the change of 1.29 km~2 was rational,the change of 0.02 km~2 was irrational,and the rationality level was Ⅰ.The rationality of land use changes in the Dianchi Lake Basin is not high,there are both rational changes and irrational changes,but the problems of irrational changes such as "should not be retreated" of cultivated land,deforestation and reclamation,lake reclamation and development,and disorderly expansion of construction land are more prominent.(3)From the perspective of the future trend of land use,the area of cultivated land,woodland,grassland and water area will continue to decrease in 2030,and the area of construction land will continue to increase.cultivated land,woodland,grassland and water area decreased by 65.36 km~2,30.54 km~2,34.62 km~2 and 7.37 km~2 respectively,and construction land increased by 137.9 km~2.Based on the above research conclusions,this paper believes that the rational utilization of land resources and lake ecological environment improvement measures in the Dianchi Lake Basin should be constructed from four aspects,namely: rationally delineating three control lines and optimizing the spatial layout of ecology,agriculture and towns;strengthen ecological protection and restoration of lake basin areas,and build a solid plateau ecological security barrier;steadily promote the conservation of intensive land,and focus on the redevelopment of low-efficiency land in cities and towns;take multiple measures to strictly control the scale of cultivated land occupation. |
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