More than half of the global population has chosen to live in urban areas than in rural areas. This results in issues on sustainable food provision in urban areas. Transporting vegetables and fruits from the countryside to the city while keeping them fresh consumes energy and causes loss. Given the cost, growing food in and around cities has never been a new thing. However, only recently, growing food on rooftops on a business scale to achieve self-reliance has increasingly gained attention. With current technological advances in horticulture and agriculture, it has become more likely to secure food provision by cultivating on urban rooftops. Only a few business scale cases reported in high-income societies with a high-density population or experiencing snowing winter can afford and justify the choice of such a high input as well as a high-yield cultivating system. In Taiwan, with a warm winter, it may be more feasible to apply this system because less energy input is required to achieve the same yield as compared to that required in places in temperate climates. By estimating the potential of a high-density city to achieve self-reliance through rooftop growing systems, decision-makers can have more insight into how the idea can be promoted. As of end 2016, Chiayi city has the second largest population density after the capital city. Thus, this research aims at assessing the potential to achieve self-reliance by growing food on rooftops in Chiayi. It analyzes the yields of four types of rooftop cultivating systems and estimates the production and consumption by using these systems on three types of rooftops in different land uses, namely commercial, educational and residential. The result shows that the best scenario for achieving self-reliance is the rooftop hydroponic greenhouse model operating at the commercial scale although this is not sustainable or practical for general households in Chiayi City.
Food security, roof garden, rooftop farms, scenario analysis, self-reliance, urban agriculture, urban farming, urban food system
 Urban agriculture; Food and Agriculture Organisation of the United Nations (FAO), available at http://www.fao.org/urban-agriculture/en/ (accessed 27 February 2017)
 United Nations, World Urbanization Prospects-The 2014 Revision, Department of Economic and Social Affairs: New York, 2014.
 Halais, F., Can urban agriculture work on a commercial scale? available at: http://citiscope.org/story/2014/can-urban-agriculture-work-commercial-scale.2014-08-21 (accessed 26 February 2017)
 Chen, B.R., Shorten the distance between urbanites and agriculture- farms are growing on rooftop of New York and Montreal, Taipeiecon, available at: http://www.taipeiecon. taipei/article_cont.aspx?MmmID=1203&MSid=654073544642016307.2015-07-01 (accessed 21 February 2017) (In Chinese)
 SAVOR...Chicag, available at: http://savorchicagomcpl.com/. (accessed 25 February 2017)
 Brooklyn Grange, available at: www.brooklyngrangefarm.com/. (accessed 6 February 2017)
 Gotham Greens, available at: http://gothamgreens.com/our-farm (accessed 21 February 2017)
 Lufa Farms, available at: http://lufa.com/en/ (accessed 21 February 2017)
 Santropol Roulant, available at: http://santropolroulant.org/ (accessed 21 February 2017)
 The Rooftop Garden Project, available at: http://www.rooftopgardens.alternatives.ca/ (accessed 21 February 2017)
 Grewal, S. & Grewal, P.C., Can cities become self-reliant in food? Cities, 29, pp. 1–11, 2012.
 Chung-Wen Elementary School, available at: http://case.cy.edu.tw/web/cwesweb/default.asp (accessed 2 March 2017) (In Chinese)
 Chiayi City Government, Revision of the Comprehensive Plan for Chiayi City, Second Edition, 2014. (In Chinese)
 Taiwan Green Productivity Foundation. Technic Guide of Energy-Saving for Supermarkets, available at: http://www.ecct.org.tw/Knowledge/knowledge_more?id=9a56fa954 4e24a50b4cba0036dfe545a 2003 (accessed 2 March 2017) (In Chinese)
 PXMART, available at: http://www.pxmart.com.tw/px/about_us_food_farm.px. 2014 (accessed 2 March 2017) (In Chinese)