Analysis of Tempo-Spatial Patterns of Beijing External Vegetable Supply and its Effects Under Massive Logistical System
以北京为例，分析了1990年代以来外部蔬菜供应的时空格局，发现供应量对数增长、空间呈西北-东南圈层结构且随季节变化，这种模式虽丰富了蔬菜来源但增加了碳排放和极端事件下的供应风险。
With the development of urbanization and logistic system,food supply pattern has been changed fundamentally in city region,of which external vegetable supply hasnot only become the majorsupplier,but also affected the vegetable diversified consumption and basic livelihood of the residents.This paper,taking Beijing as an example,analyses the tempo-spatial patterns of Beijing external vegetable supply and its effects.Two findings are identified.Firstly the amount of external vegetable supply has increased dramatically since 1990s with its market shareincreasing in a logarithm curve.Secondly the spatial pattern in vegetablespecies,supplying hinterland and seasons are explored,i.e.supplying hinterlandremaining a NW-SE directionwith an obviouscircling structure,and its main supplier varies with the season-from north to south.The effect of this pattern brings a better urban food supply because of the diversified vegetable source,but meanwhile increase the food miles dramatically with high carbon emissions.The long-distance transportation suffersfrom extreme events a lot,while the supply failure during the transition of production bases and seasonal change will also bring potential threat and risk for urban food security.Based on this analysis and conclusions,the paper puts forward some policy-oriented suggestions in the last part.