| The arid desert area in Northwest China has dry climate,scarce rainfall and negative balance of soil moisture for a long time,which seriously restricts the evolution of local regional ecosystem and the change of water and soil environment.It is a typical fragile area of resources and environment in China.The establishment of artificial ecological oasis by means of water lifting irrigation has become a practical and effective way to realize the development and utilization of water and soil resources in arid desert areas.However,the outward injection of water resources is actually an artificial importation of the most sensitive impact factor-water-into the arid desert area.This driving process is impacted by the complexity,typicality and uniqueness of the soil and water resource background in the artificial oasis in the arid desert area,and its spatial and temporal differentiation process shows obvious multifactor participation,multi-level driving and multi-process coupling characteristics.With the population growth and economic development,the contradiction between the demand for soil and water resources and their constraint,scarcity and finiteness has been highlighted and intensified.How to achieve optimal spatial and temporal allocation of soil and water resources and green and sustainable development of soil and water resources under the "double carbon background" has become a prerequisite for exploring the balance mechanism between ecosystem protection and production demand in arid desert areas.In order to achieve the optimal spatial and temporal allocation of water and soil resources and the green and sustainable development of water and soil resources,it is necessary to clarify their intrinsic evolutionary mechanisms and spatial and temporal differentiation processes.However,due to the complex topography and diversified geomorphological units in the northwest arid desert region,the natural geographic differentiation between regions is obvious,and due to the influence of spatial movement of water resources and spatial fixity of land resources,the accurate revelation of the coupling mechanism and mutual feeder response process between them is still insufficient,and the medium and long-term resource carrying capacity prediction research in the context of coupled water and land resources still needs further exploration.In view of this,this paper takes Jingtai Chuan electric power irrigation area in Gansu Province as the research area and focuses on the key issue of the multi-scale coupling relationship between water and soil resources and their comprehensive spatio-temporal variation of carrying capacity in the context of water lifting and irrigation.The system dynamics,PSR model and multi-level fuzzy theory are introduced to analyze the system problem of water and soil resources carrying capacity of irrigation area with high order,multiple feedback and complex time variation.Long series monitoring,spatial telemetry,UAV aerial photography and economic and social data are assimilated and integrated to reveal the spatial and temporal variation characteristics of soil and water resources bearing factors and comprehensive bearing capacity in the irrigation area from three driving processes: geological and climatic driving,soil and water environmental driving and natural-human driving.On this basis,the water and soil resources bearing status of four typical monitoring nodes in the irrigation area in 1994,2002,2010 and 2018 were comprehensively assessed by introducing the physical element analysis model and cloud model,respectively.Finally,a spatial and temporal evolution prediction model of soil and water resources carrying capacity at regional scale based on the combination of numerical and spatial analysis is constructed based on the theoretical basis of the meta-automata-Markov model(CA-Markov).The spatial and temporal variation of soil and water resource carrying capacity in the irrigation area in the medium and long term is predicted and analyzed in future scenarios.It is expected to provide a useful reference for seeking a balance between production demand and ecological conservation of soil and water resources in the irrigation area under the "double carbon background".The main findings of the paper are as follows.(1)The elevation range of the irrigation area is between 1512 m and 2237 m,and the high elevation area is mainly concentrated in the western part of the irrigation area;The surface slope of the irrigation area is between 0° and 9.0°;Influenced by temperate continental climate,the annual evaporation is between 2292 mm and 2316 mm,and the annual precipitation is only about 180 mm,the spatial variability is relatively small;The four soil physicochemical factors,surface soil salinity,soil salinity,surface soil conductivity and soil conductivity,characterize a significant increment in spatiality with time series;Influenced by irrigation patterns and hydrogeological conditions,the average groundwater depth of burial in the irrigation area decreased by 4.55 m during 1994-2018,and the average groundwater mineralization increased by 1.31g/L,indicating that the soil salinization in the irrigation area has been increasing,and it shows the spatial pattern of the closed hydrogeological unit in the northeast is increasing in an arc-shape toward the central and northwest.(2)With the improvement of water distribution facilities and the increase of water demand,the overall vegetation cover within the irrigation area characterizes the spatial and temporal divergence of transition from low cover to high cover.The very low coverage area decreased by 39869.28 hm2 during 1994-2018,and the high coverage area increased by45358.02 hm2 during 1994-2018;the coordination degree of soil and water was also in a state of continuous improvement during 1994-2018,with the average value increasing from 0.28 in1994 to 0.89 in 2018,but the overall drought base was still relatively large,and it is especially drastic in areas near Gobi,wasteland and other land types such as Zhitan Township and Xijing Township;the light and heat conditions such as surface temperature and surface albedo in the irrigation area also gradually evolve from a non-stable state to a stable state with the development and utilization of the irrigation area.(3)With the development and utilization of soil and water resources in the irrigation area,the average land pollution load increased by 3.12 kg·hm-2 between 1994 and 2018,and the high load areas are mainly concentrated in towns and areas with relatively high population density;The overall spatial and temporal evolution of land use types in the irrigation area shows an increase in the area of cultivated land,a decrease in the area of Gobi and uncultivated land,and an expansion of the area of Gobi,grassland and uncultivated land between 1994 and 2018.The spatial pattern of land use types in the irrigation area shows an increase in the area of cultivated land,a decrease in the area of Gobi and uncultivated land,and an expansion in the area of land for construction and transportation and salinization,with the Gobi,grassland,sandy land and uncultivated land contracting by 28,802 hm2,8,314 hm2 and 23,869 hm2,respectively,and the cultivated land,lightly salinized land and moderately salinized land expanding by 52,127 hm2,2,382 hm2 and 181 hm2,respectively,between 1994 and 2018.increased by 16.89 person-hm-2 during 1994-2018,reflecting that the degree of human habitability in the irrigation area is also increasing.(4)Based on the analysis results of the physical element analysis model,the water and soil resources bearing states of the irrigation area in 1994,2002,2010 and 2018 are "V2-slight bearing","V3-critical bearing","V3-critical bearing","V4-bearing security",respectively." V3-critical bearing","V4-bearing security";based on the cloud model evaluation results,it can be seen that the corresponding cloud numerical characteristics of each study node are C1994(0.4467,0.0248,0.0058),C2002(0.5034,0.0236,0.0071),C2010(0.5586,0.0218,0.0062),C2018(0.5989,0.0249,0.0061)The bearing status of soil and water resources in each period of the irrigation area are "slight bearing ~ critical bearing","critical bearing","critical bearing ~ good bearing" and "critical bearing ~ good bearing".The evaluation results of the two models are basically consistent,reflecting that the water and soil resources in the irrigation area are in a "healthy" and "continuous" evolution process,but due to the environmental background and resource development mode,this "healthy" evolution rate shows a slowdown.However,due to the environmental background and resource development pattern,this "healthy" evolution rate shows a slowing down trend.(5)The spatial and temporal evolution pattern of water and soil resources bearing status of the irrigation area in 1994-2018 is Severe bearing area and slight bearing area are reduced,and the area of critical bearing area,safe bearing area and good bearing area is gradually increased.The serious bearing areas are mainly concentrated in the areas of Zhitan Township,Xijing Township,southern Manshuitan Township and northern Shang Shawo Township.The patterns of changes in the characteristics of each load-bearing area in the irrigation area from large to small are as follows: continuous change type>pre-change type>later change type>continuous stable type>repeated change type.The maximum spatial transfer area patterns of soil and water resources during 1994-2002,2002-2010 and2010-2018 are: "severe carrying capacity-slight carrying capacity","critical carrying capacity-safe carrying capacity","safe carrying capacity-good carrying capacity".".This indicates that the overall soil and water resources bearing status of the irrigation area is in a positive evolution mode.(6)Based on the MCE method of Boolean operations,the water and soil resource bearing state of the irrigation area in 2018 was simulated with the CA-Markov module in IDRISI and the Spatial Analysis tool of Arc GIS10.1.The overall mean value of simulation accuracy was 94.78%,which verified the reliability of model prediction.On this basis,the spatial distribution of soil and water resources bearing state in 2026(medium term)and 2034(long term)in the irrigation area was simulated.The results show that the overall spatial characterization of soil and water resources bearing state in the irrigation area during2018-2034 is a trend of healthy evolution.However,combined with the overall variability of each bearing characteristic,this benign evolution trend is gradually slowing down,and the slightly bearing and severely bearing areas gradually show a spatial transition from desertification to salinization and urbanization. |
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