The Research On Dynamic Evolution Of Global Wheat Trade Network Under Climate Change

Climate change and food security are important issues.Plents of literatures found that weather uncertainties and natural disasters caused by climate change have seriously affected crop production,especially in developing countries with weak "adaptability".These countries import crops from the global market for balancing domestic food supply and demand and enhancing food security.In recent years,many large crop exporters,like the US and some countries in Europe,import more crops and export less crops for developing biomass energy,which makes global crop market more complex.Therefore,the complexity of global crop trade had been one of the most important questions for scholars and countries.Besides,the study of wheat,the largest trade crop,can provide an important reference for other crops.Based on previous literatures,this paper focused on one of main crop wheat,and studied the impact of climate change on global wheat trade and the evolution of global wheat-trading network structure,and the evolution of community and competition for global wheat trade under climate change using different methods including statistics,econometrics,complex networks and so on.The research not only enriched the theory of the association between climate change and socio-economic,but also provided some references for countries tackling climate change and making policies and suggestions.Main results and innovations were shown as follows.(1)This paper constructed the model of climate change and global wheat export.Considering regional differences and the correlation between temperature and precipitation,we also established a novel extended model to study the impact of weather on global wheat export,which revealed the association between climate change and global wheat trade.The study expanded the research on the social and economic impacts of climate change.In this paper,we constructed the dataset including temperature,precipitation and global wheat trade and so on.From the export perspective,fixed effect model was applied to study the association between the weather and global wheat export.Then we considered regional differences and the correlation between temperature and precipitation and explored the impact of precipitation in different regions and the moderate effect of temperature.Finally,growing-season,socioeconomic factors and the lag of atmospheric facors were considered in the models to test the robustness of the results.The results showed that there was a significant negative association between precipitation and global wheat export.However,this paper did not find a significant association between temperature and global wheat export.A second finding was spatial heterogeneous precipitation effect.Precipitation in high-precipitation countries was substantially associated with wheat export growth.Finally,this study found temperature influenced the effect of precipitation on global wheat trade.There was a significant difference between hot countries and cool countries and the impact of precipitation was greater in high-precipitation and hot countries.(2)This paper firstly constructed global wheat-trading network and proposed a novel indicator Network Gini coefficient.We also constructed the model of climate change and the structure of global wheat trade and studied the impacts of temperature and precipitation on the evolution of global wheat-trading network.The study provided a new perspective on the impact of the evolution of global food trade in the further.In this paper,global wheat-trading network was constructed using complex network theory and analyzed the heterogeneity of global wheat trade network based on the Network Gini coefficient.Then continuous core-periphery model was applied to analyze each country's importance in the trade network.Finally,this paper studied the association between atmospheric factors and heterogeneity evolution of wheat-trading network.Several results were found in this paper.Firstly,there was a strong heterogeneity in the global wheat-trading network,which showed an increasing trend.Secondly,the status of countries in the global wheat-trading network were obviously different.The status of large wheat exporters,such as the US and Canada,were higher,while the status of countries in Africa,Northern Europe,Central Asia were lower.Finally,this study found that precipitation was associated with the evolution of the wheat-trading network.Precipitation positively influenced the trade status of “core countries”,while precipitation had no significant effect on “periphery countries” in the network,which contributed to the heterogeneity of global wheat network structure.(3)This paper constructed dynamic model of global weighted wheat-trading network using complex network theory and established a community division model of global wheat trade.Besides,an indicator Normalized Mutual information of global wheat trade was proposed to analyze the stability of communities,and the evolution law of clustering was revealed in this paper.The study ecriched the work of global food trade,and provided new ideas for further research on the evolution of global food trade.This paper constructured global weigthed wheat-trading network using complex network theory.Then the community division model based on modularity was introduced in this paper to divide the network.We studied the evolution of community and its members and explored its reasons.The results showed that there was heterogeneity for the distribution of global wheat trade,and some communities contained many countries,while some communities contained few countries.Secondly,due to the fluctuation of trade strategies with global wheat price and other factors,the members in the communities of global wheat trade were not stable,and small communities constantly emerged into and divided from large communities.However,the clustering of global weigthed wheat-trading network gradually stabilized over time.Finally,this paper found that climate change rather than geographical factor might affect the evolution of communities.(4)This paper constructed global wheat-trading competition network using complex network theory,and proposed a new indicator “competitive intensity” that is treated as the edges' weight in this paper.We also constructed global weighted wheat-trading competition network and studied the evolution of direct and the indirect competitive relationships.Meanwhile,this paper established the model of the impact of climate change on the evolution of global wheat-trading competition network and revealed the mechanism of climate change on global wheat-trading competition.The work improved the research on the impact of climate change on competition in food trade.From the perspective of import,this paper constructed global wheat-trading competition network using complex network theory.Besides,four network topology indicators,discrete core-periphery model and “competitive intensity” are chosen for studying the evolution of global wheat-trading competition network.Finally,this paper analyzed the association between climate change and the evolution of global wheat-trading competition network and explored its mechanism.The results showed that,firstly,the competition widely existed in the wheat importers,while the competitive pressure of global wheat trade was decreasing with time.Secondly,although the core countries of the competition network were dispersed,the core-periphery structure of global wheat-trading network became clear over time,and core countries of competition tended to be stable,mainly locating in Asia and Africa and dominating the evolution of competition network.Thirdly,Italy,Japan and other large wheat imports were not only the main driving force for evolution of the competition pattern,but also played important roles in transferring wheattrading competition.Finally,this paper found that precipitation significantly influenced the evolution of global wheat-trading competition network and wheat export was one of the mechanisms for this association.