| With the influence of global climate change and human activities,a series of water security problems have become increasingly prominent in Dongting Lake Basin in recent years,such as climate drying,water conservation function weakening,water pollution,water shortage,groundwater level decreasing,frequent flood disasters.Territorial space is an important spatial carrier for human production and living,social and economic activities,and the construction of ecological civilization.Territorial space planning is the spatial and temporal arrangement for the development and protection of a certain regional territorial space,the guide for national spatial development,the spatial blueprint for sustainable development,and the basic basis for all kinds of development,protection and construction activities.We will use water to define cities,land,people and production,so as to form a spatial layout that matches water resources,water environment,water ecology and water security.Therefore,as a constraint factor,how to arrange the territorial space more scientifically has become a scientific problem to be solved.Taking Dongting Lake Basin as the research object,based on five phases of land cover data in 2000,2005,2010,2015 and 2020,using ArcGIS as the data processing platform and using system dynamics,PLUS model and other methods,this paper carried out simulation and optimization research on the spatial distribution of Dongting Lake Basin under the constraint of water security pattern.The main research achievements are as follows:(1)The spatial classification system of Dongting Lake Basin was constructed,and the evolution characteristics and influencing factors of spatial distribution of Dongting Lake Basin were analyzed from 2000 to 2020.The results showed that:①Forest land was the matrix type of the spatial distribution of Dongting Lake Basin,and the aggregation degree was the highest;The shape of patches in land waters is the most complex.The fragmentation degree of cultivated land is the highest,the segmentation degree of village construction land is the highest and the spatial distribution is the most discrete.Village construction land,garden land and urban construction land are most strongly affected by human activities.②From 2000 to 2020,the area of forest land first increased and then decreased,the area of garden land and wetland increased slowly,the area of grassland and cultivated land decreased,the area of land and water fluctuated,and the area of urban and village construction land increased with the increase of construction intensity.③The fragmentation degree of territorial space in Dongting Lake Basin increased,the landscape heterogeneity increased,and the distribution of territorial spatial patches tended to be uniform.④The best factors affecting the evolution of regional territorial spatial distribution were "elevation,soil type,biodiversity value,distance from administrative center,annual gross output value of primary industry,annual gross output value of secondary industry,annual population distribution,annual sales of consumer goods,annual fixed assets investment",and the best research step was 10 years.(2)Conduct 2000-2020 water security status evaluation from three aspects:the importance of water resources protection,water environment security and comprehensive risk of water disasters,identify water resources security pattern,water environment security pattern and water disaster avoidance security pattern respectively,and identify comprehensive water security pattern based on the three single water security patterns.The evolution characteristics of water security pattern in Dongting Lake Basin were analyzed from three aspects:structure evolution,importance grade area transfer and importance transfer,and the main obstacle factors of water security in Dongting Lake Basin were diagnosed.The results showed that:①The water body of Dongting Lake,the Dongjiang reservoir and the main rivers had high scores on the importance of water resources protection;The risk of water environment security is the highest in the west and southeast of Dongting Lake Basin.High water disaster risk values were mainly concentrated in the northeastern,eastern and central regions of the study area.②The importance of integrated water security pattern in the northeast,central and southeast Dongting Lake Basin is the highest,while the importance of integrated water security pattern in the west is low.③In the water security pattern,the areas of the more important and the moderately important areas were the widest.The importance of water environment security pattern increased sharply across levels.The importance of water security pattern migrated eastward during 2000-2005,and the spatial distribution of the importance of comprehensive water security pattern was stable during 2005-2020.④The main obstacle factors of water resource security,water environment security and water disaster risk in Dongting Lake Basin are water resource background condition,water environment security state factor and disaster bearing body exposure factor respectively.(3)Set the water security pattern Ⅰ～Ⅴ constraint scenarios,construct the SD-PLUS quantity-space coupling model,and expand the natural expansion scenario prediction of territorial spatial layout;A method of territorial spatial distribution constrained by water security pattern is proposed to forecast the territorial spatial distribution of Dongting Lake Basin under the constraint of water security pattern in 2025,2035 and 2050.The results show that:①Under the natural expansion scenario,the spatial distribution structure of Dongting Lake Basin basically maintains a stable state.②Under the five-level constraint scenario prediction of comprehensive water security pattern,the spatial structure of the Dongting Lake Basin remained basically unchanged,but the rate of change changed.Woodland was always the most important spatial type of the Dongting Lake Basin,followed by cultivated land.(4)Make a statistical analysis of the territorial space composition in each important area of the water safety pattern under each constraint scenario during 2020-2050,determine the optimal constraint scenario of the water security pattern according to the principle of optimal selection,and take the forecast results as the optimization objectives for the near(2025),middle(2035)and far(2050)periods.We will optimize the spatial distribution of the Dongting Lake Basin.The results showed that:①In 2020,the main types of land space in the areas of extremely important water security pattern were land water and forest land,and the proportion of land water area was more than 50%;The main types of land space in the areas of high importance,medium importance,relatively importance and general importance are woodland and cultivated land.②In 2025,2035 and 2050,the area of all land types of ecological space will decrease slowly,the area of urban construction land and village construction land will increase slowly,and the area of cultivated land will keep stable basically.③The optimal water security pattern constraint scenario was Ⅲ level water security pattern constraint scenario.④Suggestions for the territorial space optimization of Dongting Lake Basin are put forward:the development concept of "jointly pursuing large-scale protection,not large-scale development" should be effectively implemented;Promoting ecological dredging of rivers and lakes in Dongting Lake Basin to accelerate ecological recovery of Dongting Lake Basin;Grasp the main obstacle factors and improve the level of water security in the basin.Based on the urgency of the research on water security of Dongting Lake Basin and the scientific consideration of the research on territorial spatial distribution at the scale of the basin,this paper analyzes the evolution characteristics of territorial spatial distribution of Dongting Lake Basin,identifies the water security pattern of Dongting Lake Basin,takes it as the constraint condition of the future territorial spatial distribution of Dongting Lake Basin,and carries out simulation and optimization research on territorial spatial distribution.In order to provide scientific guidance for the territorial spatial planning of Dongting Lake basin,the optimization objectives and countermeasures are put forward. |
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