Simulation Research On Water Resources Policy Effects From The Perspective Of Water-energy-food Nexus

As indispensable resource for human survival and development,the relationship among water,energy,and food is getting closer.The conflict between water security,energy security,and food security has gradually become prominent.It has become a new constraint that constrains sustainable development and the construction of ecological civilization and national security system.In recent years,the water-energy-food nexus has attracted international attention.This means that problems or policies from any one field have an increasingly important impact on other fields.Therefore,in the formulation of water resource policies,theoretically,the "nexus" and the transmission mechanism of water resource policies based on this should be considered.However,in practice,China's water resource policies are still mainly oriented toward water saving,lacking a comprehensive grasp of the water-energy-food nexus,and they may affect the balance of the nexus.In the long run,water resource policies under a single water-saving goal may affect the balance of the water-energy-food nexus,and the effectiveness of water resources policies will be also greatly reduced.Therefore,from a theoretical point of view,it is necessary to promote the theoretical study of the water-energy-food nexus,find new ideas in economics for the study of water resource from the perspective of the waterenergy-food nexus,and extended the assessment of policy effect under the framework of water-energy-food nexus.From the perspective of practical needs,it is important to promote the enrichment and deepening of empirical research on the water-energy-food nexus in China and explore a way to alleviate the conflicts between water security,energy security,and food security in China.Both of them have certain guiding significance for the selection and coordination of China's water resources policies at this stage.At present,in the research on nexus,there are relatively rich research results in the field of natural sciences and technology,while ther are few researches in social sciences,especially in the field of economics,and the institutional level.In particular,there is insufficient analysis of the causes and characteristics of nexus.These have limited the further development of related research from the perspective of nexus.In the research on water resource policy,the existing water resource policy CGE model and waterenergy relationship coupling model essentially has not been placed under framework of the water-energy-food nexus.There is also a lack of discussion on the effect of water resources policy combination.These can no longer meet the current and future practical needs.Therefore,the economic analysis ideas of water-energy-food nexus were explored at first.Based on the basic theories of economics,it was proposed that the economic cause of the water-energy-food nexus was the industrial linkage and externalities between the three industries of water supply,energy production and food production.The internal mechanism of water-energy-food nexus was summarized as a combination of the dynamic transmission of longitudinal shocks within subsystems over time and the lateral shock transmission between subsystems.secondly,the CGE model of China's water policy analysis was constructed to simulate and analyze the effects of the single water resource policy and policy combination from the perspective of the water-energy-food nexus.Based on the data of China's three industrial sectors from 1997 to 2016,a structural vector autoregressive(SVAR)model was constructed to empirically test the mechanism of water-energy-food nexus proposed above.The characteristics of China's nexus were summarized,the resource policy basis and path selection from the perspective of nexus was explored,and the theoretical research and the empirical research on the waterenergy-food nexus in China has been enriched to a certain extent.All these provide a sufficient theoretical guarantee for the construction of water resources policy analysis model from the perspective of water-energy-food nexus.Combined with the theory of general equilibrium,a computable general equilibrium(CGE)model for water resources policy analysis was designed,the SAM table with a base period of 2017 including 29 accounts was compiled,and the modeling was implemented by using GAMS software programming.The CGE model of China's water resource policy analysis from the perspective of water-energy-food nexus was constructed,and the tool system for China's water resource policy research was expanded.Based on the relevant theories of water resources policy,different policy shock scenarios were designed to simulate and analyze the direct effects of a single water price policy,water resource tax policy,and water resource fiscal expenditure policy on water resources related variables,and the indirect effects of energy and food related variables,and the comprehensive effects are evaluated.The features and principles of each policy were summarized,three water resource policies were classified according to their effects,and the improvement of the comprehensive effects of each policy combination was analyzed.Recommendations on the choice and combination of water resources policies from the perspective of the nexus were put forward.The conclusions of this study are as follows:First of all,the emergence of the water-energy-food nexus was related to the development of high water-consuming energy production.In the empirical study of China's water-energy-food nexus based on the participation of different types of energy,the water-energy-food nexus with the participation of nuclear power and natural gas was significant,while the water-energy-food nexus with the participation of crude oil was not significant.Second,according to two manifestations of China's water-energy-food nexus,the characteristics of China's nexus were summarized.The two manifestations were based on different energy types,namely:the water-energy-food nexus with the participation of nuclear power and the water-energy-food nexus with the participation of natural gas.The characteristics of China's water-energy-food nexus were derived.For the interactions of the water-energy segment in China's water-energy-food nexus,the conduction from energy to water was consistent for different types of energy,while that from water to energy varied depending on the type of energy.Food production always had a negative impact on energy production,while the conduction from energy to food varied for different types of energy.The conduction between food and the water supply was not as significant as was generally considered.Especially,the impact of the water supply on food production was weak.At the same time,the order of strength intensity and the duration were also available for reference.Third,the three water resource policies discussed in this study were divided into two categories in terms of effectiveness:the first category was water price policies,and the second category included water resource tax and water resource fiscal expenditure.They both had some characteristics.The first category,which had diminishing marginal net income,had obvious effects in controlling the relative equilibrium quantity of water resources,food,and energy,but it was easy to cause fluctuations of other variables in the economic system.The second category,which had a small marginal net income,was relatively weak in controlling the relative equilibrium quantity of water resources,food and energy,but it only caused relatively small fluctuations on other variables in the economic system.In addition,In the second category of policies,the effects of the water resource tax policy and the water resource fiscal expenditure policy were very close,but the functioning principles of the two and their impact on the supply and demand sides were different.From the perspective of the impact on both the supply and demand sides,the water resource tax policy had a greater impact on the demand side than on the supply side,mainly reducing the water demand on the water demand side,while the water resource fiscal expenditure policy had a relatively greater impact on the water supply side than on the demand side.In addition,water resource fiscal expenditures policy will cause equilibrium prices to fall rather than increase,which was different from water price policies and water resource policies.What's more,from the perspective of the water-energy-food nexus,the water resource policy had a more obvious impact on the energy market than on the food market.The empirical test results based on the SVAR model showed that the relationship of water-energy segment in the nexus was more obvious than the relationship of water-food segment.The policy simulation results based on the CGE model also showed that the indirect effects of the three water resources policies on energy were greater than the indirect effects on food.Last but not least,it was the key to determine whether the policy combination had obvious value whether there were obvious differences between water resource policies.The combination of dual policies between different types can significantly improve the overall effect,which can complement each other's advantages and offset costs.The combinations with the existence of similar water resources policies,including a combination of similar double policies and a combination of three policies with similar policies,were of little significance to the overall effect improvement.Because of the different impacts of the two policies on both supply and demand in the second category of policies,there was also a specific application scenario for the dual policy combination of "vater resource tax+water resource fiscal expenditure",that was,when the policy goal focused on moderate comprehensive effects and further guidance for the balance of water supply and demand.It was not obviously necessary to adopt a threepolicy combination of "water price policy+water resource tax policy+water resource fiscal expenditure" to improve the overall effect.