Uploaded on 2017-02-08 by Helen Chen

1. In the urban districts in Shanghai, one example of stocks and flows on the time scale of day(s) is packaging material like Styrofoam boxes. In the morning, these boxes enter the district as packaging material for wet market suppliers such as fruits, vegetables and seafood. They stay in the markets until the evening when the styrofoam collectors carry the empty containers out of the district. It is good that the materials are getting recycled and reused, however the situation can be better we can reduce the amount of stocks and flows of styrofoam through a new distribution paradigm, or use more sustainable materials. 2. Migrant workers represent another important example of stocks and flows, but on the time scales of months to a year. We just saw the biggest people movement within China which happens once a year during the Chinese New Year holidays. Shanghai has millions of migrant workers who come after Chinese New Year from all parts of the country, live and work in Shanghai during the year, and go home just before the next New Year. The city streets are quite empty during the holidays! As China as a whole develops, the flow is likely to change. At the same time, Shanghai has announced policies to limit the number of residents, thus curbing the “stock” of inhabitants. One of the challenges now is to find more comfortable, energy efficient ways to support the stock and flow of migrant workers to reduce the city’s carbon footprint. 3. On longer time scale the stocks and flows of urban greenery (trees, landscape, etc.) within a city also change. Just over a hundred years ago, what is now Shanghai is mostly covered with agricultural land or natural landscape, then over the last century the land has been transformed into a dense forest of buildings. The transformation of rural and green spaces into urban development is still happening as shown in the image. However, slowly within the past decade or so the city has been reintroducing more flow of green scape into the city, in parks and eco corridors. Perhaps at some point the city can achieve a healthy balance in the flow of green spaces.