Development Of Quantitative Method Of Inter-provincial Grain Trade And Evaluation Of Virtual Water Flow Pattern In China

Since the reform and opening up,the center of China’s grain production has experienced a gradual westward and northward shift.The grain trade has changed from the pattern of grain trade from the south to the north,to the pattern of grain trade from the north to the south.This pattern of grain trade has exacerbated pressure on water resources and ecology in the northern region,and threatened China’s food security.Therefore,it is of great significance to quantitatively assess the inter-provincial grain-related virtual water flow in China.However,many studies quantified grain virtual water flow based on different assumptions due to the lack of grain trade data among regions in China,which reduces calculation accuracy.The paper takes 31 provinces of China as research units,evaluates impacts of the basic driving factors of grain trade(transport cost,net grain imports and differences in dietary structure between provinces)on regional grain trade and develops a new multi-objective linear optimization model to quantify grain trade based on weights of different drivers.Then we evaluate associated effects of grain virtual water flow.At the same time,we compare the differences among quantitative models of grain trade,and then analyze the characteristics of the model in the paper.The main results are as follows:(1)Analyzing the influence of different driving factors on China’s inter-regional grain trade.It was found that transport cost of grain(including distance and transport cost),differences in dietary structure between provinces,and net grain imports are the main drivers of China’s inter-regional food trade,except for grain surpluses and deficits.China’s grain supply and demand relationship is uneven(supply is less than demand)when net food imports are not considered.Therefore,considering net grain imports is a prerequisite for accurately quantifying regional grain trade.The transport cost is the most basic driving factor of grain trade that has been widely discussed,but the transport cost at this stage involves only transportation distance.At the same time,due to the obvious regional differences in China’s dietary culture,the differences in regional dietary structure significantly influence the direction of grain trade.The results of entropy method show that the weights of transport cost and regional differences in dietary structure on grain trade are0.665 and 0.335,respectively,indicating that the impact of transport cost on grain trade at this stage is higher than dietary structure differences.(2)Developing a multi-objective linear optimization model to quantify grain trade and evaluating the associated effects of grain virtual water flow.The model takes the global minimum of transport cost and differences in dietary structure between provinces as theobjective function,and takes the conservation of grin mass as constraints.The differences in dietary structure are characterized by the Euclidean distance on the consumption of rations and animal products in each province.The transport cost is cost with simultaneously considering distance and modes.The quantitative results show that China’s grain trade from north to south in 2015.The virtual water flow imbedded in grain trade is 98.38 Gm3,accounting for 15% of the total water consumption of grain production.(3)Revealing the associated effects caused by the inter-provincial grain-related virtual water flow.The associated effects are different by several models.However,in general,the grain virtual water content in grain-exporting regions is smaller than that in grain-importing regions,so grain trade has a water-saving effect at the national scale.However,grain virtual water flow from the water-scarce and underdeveloped northern region to the water-rich and economically developed southern region.The flow pattern increases the pressure of water resources and ecology in the north and widens the economic difference between the south and the north,which is not conducive to the sustainability of food production.Therefore,from the perspective of resource consumption,economic development and the sustainability of food production,the virtual water flow of grain at this stage is unreasonable.(4)The multi-objective linear optimization model reduces data hypothesis and adds driving factors,thereby improving the credibility of calculation results and expanding application scope of the model.The paper compares and analyzes difference between the developed model and several other typical quantitative models.The multi-objective linear optimization model reduces data assumptions(such as not considering actual grain import and transport modes of grain).Meanwhile,based on the existing models,we have gradually improved the research on the drivers impact of food trade,and achieved a comprehensive quantitative change from a single driver to multiple drivers.The model quantified virtual water from the perspective of driving impacts and precluded the limitations of trade data.The model can be used in other countries and regions,where trade data is difficult to obtain,to calculate trade patterns.