Optimization Of "Water-energy-food-carbon" Ecosystem Service Function In The Middle And Lower Reaches Of The Datong River Basin

Water,energy,and food are the most fundamental supply resources in human production and life,providing essential ecosystem services to humans.Carbon sequestration,as another important regulatory function,is also crucial for achieving carbon neutrality and peak carbon emissions in our country’s current context,contributing to social green development.With the deepening interaction among resources and functions,excessive focus on a single element in the past can lead to exacerbated supply-demand conflicts and regional imbalances.In this context,exploring and optimizing the relationships between water,energy,food,carbon resources,and their functions from a nexus perspective is essential for achieving regional sustainable development.The Datong River is an important tributary of the Yellow River,with abundant water resources,high intensity of hydropower development,a long history of agriculture and animal husbandry,and high vegetation productivity,playing a crucial role in the socioeconomic development and ecological security of the middle and lower reaches.Therefore,it is necessary to comprehensively consider the "water-energy-food-carbon" nexus in the Datong River Basin,optimize the future development path of agriculture and animal husbandry,and achieve integrated management and multi-objective development of the ecosystem in the Datong River Basin.Based on the past climate,hydrological,and socio-economic background of the study area,this study combined the eco-hydrological(SWAT)model and System Dynamics(SD)model to construct a simulation model for the "water-energy-foodcarbon" system in the middle and lower reaches of the Datong River Basin.Furthermore,simulation was conducted for the water yield,hydropower generation,food production(including crop cultivation and livestock breeding),and carbon sequestration service from 2000 to 2019,with corresponding statistical monitoring data used for validation.Using the validated model,the study simulated the carbon sequestration,net selfproduced water quantity,and direct economic output of the study area under different emission scenarios(SSP1-2.6,2-4.5,5-8.5)and socio-economic development pathways(maintenance of the status quo,agricultural expansion,ecological development,livestock development)for the future from 2020 to 2099.These were then converted into total economic value based on certain criteria.By comparing the simulation results of each combination scenario,the study selected the regional development path with the highest total economic value output for future development in the middle and lower reaches of the Datong River basin,providing a reference basis for future development in the area.The main conclusions of this article are as follows:(1)The study area has experienced a significant warming trend over the past 50 years and is projected to continue warming at a rate of 1.2°C per decade over the next80 years.However,precipitation is projected to increase significantly at a rate of 13-24 mm per decade only under the high and medium emission scenarios.Human activities in the study area have gradually intensified since 2000.The average net self-sustaining water yield is 850 million cubic meters per year,but it has significantly decreased at a rate of 160 million cubic meters per decade over the past 20 years.Hydropower generation,direct economic output,and carbon sequestration have all shown significant increases,reaching 420 million kilowatt-hours,1.0 billion yuan,and 2.384 million tons,respectively,in 2019.(2)The "water-energy-food-carbon" simulation model constructed in this paper using the SWAT hydrological model and System Dynamics model has good applicability in the middle and lower reaches of the Datong River Basin.The correlation coefficients of the SWAT hydrological model during the calibration and validation periods in the study area are both above 0.8.The relative errors of the simulated values of the four main service functions in the historical period by the "water-energy-foodcarbon" simulation model are generally within 15%.(3)In the future,under low,medium,and high climate emission scenarios,the study area’s self-generated water yield significantly increases compared to historical periods,with a growth rate of approximately 14% to 26%.Further analysis,considering different climate scenarios combined with socioeconomic scenarios,reveals that the carbon sequestration,net self-generated water yield,and direct economic output in the study area exhibit varying characteristics depending on the comprehensive scenario.Overall,the regional economic value shows an increase,with fluctuations ranging from5% to 51%.By comparing different scenarios,it is concluded that the moderate expansion of agriculture is the most suitable scenario for the future development of the region.The total economic value in this comprehensive development scenario is projected to reach 3.2 to 3.4 billion yuan.Compared to other scenarios,this scenario sacrifices 23% of net self-generated water yield in exchange for a 3% increase in carbon sequestration and a 55% increase in direct economic output,resulting in a 17% increase in total economic value.Therefore,it is recommended that the middle and lower reaches of the Datong River Basin appropriately expand the arable land area,adjust the crop structure,while maintaining the continued growth of the livestock industry at the current pace.(4)Please note that the optimal development path will change with the change of different resource prices.When the unit price of carbon or water resources exceeds a certain threshold,the optimal development scenario for the basin will also change.According to the current resource market prices used in this paper(carbon unit price of58.5 yuan/ton and water unit price of 1.17 yuan/m3),it is currently difficult to fully stimulate the development enthusiasm of areas like the Datong River Basin to enhance the ecosystem services of carbon sequestration and water production.