PhD defence
The opportunities for urban food self-sufficiency through green roofs: Modeling, Optimization, and Policy Scenario Analysis
- P. Xie
- Date
- Wednesday 8 April 2026
- Time
- Address
-
Academy Building
Rapenburg 73
2311 GJ Leiden
Supervisor(s)
Summary
Cities rely on long supply chains for fresh food, which can be disrupted by extreme weather, geopolitical shocks, and transport bottlenecks. This thesis asks how much underused roof space could help, and what trade-offs come with it, by turning suitable flat roofs into productive green roofs that grow vegetables while also managing rainwater.
I combined detailed roof maps (building footprints, height data etc) with a crop growth model to estimate yields, then used optimization to design crop mixes that best match local food demand. Amsterdam is used as a case study, and the approach is then scaled up to 626 European cities.
For Amsterdam, I identified about 396 hectares of suitable flat roofs (around 16% of the city’s roof area). These roofs could produce up to 28,000 tonnes of vegetables per year, and with an optimized crop mix could cover roughly 70% of the city’s demand for a basket of common fresh vegetables. However, maximizing food production can reduce rainwater retention: irrigated systems raised yields but retained less rainfall than rainfed systems.
Across Europe, rooftop production could cover on average 30–40% of vegetable demand under irrigation, but results varied widely depending on roof area, climate, and population growth. These findings are special because they provide a roof-by-roof, city-scale estimate of both food and water benefits, helping planners compare realistic options. Overall, rooftop farming will not replace regional food systems, but it can provide a meaningful local buffer that improves resilience and delivers co-benefits such as stormwater control and climate adaptation.
PhD dissertations
Approximately one week after the defence, PhD dissertations by Leiden PhD students are available digitally through the Leiden Repository, that offers free access to these PhD dissertations. Please note that in some cases a dissertation may be under embargo temporarily and access to its full-text version will only be granted later.
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