In the face of accelerating climate change and environmental degradation, cities are increasingly defined by zones of heightened vulnerability, what we term "red zones". These are urban areas marked by environmental risks and entangled social conflicts such as extreme heat, flooding, drought, soil contamination, and toxic waste. Unlike the so-called "blue zones", where favorable conditions support longevity and well-being, red zones represent concentrated areas of exposure, where both environmental and social stressors threaten the habitability of urban life. Red zones are not just places of danger – they are sites where the future of urban resilience is contested, negotiated, and reimagined. One of the most pervasive risks is urban overheating. As global temperatures rise, densely built environments become heat islands, absorbing and retaining warmth to dangerous levels. Vulnerable populations, particularly the elderly, children, and individuals with health conditions, are disproportionately affected. Prolonged exposure to excessive heat exacerbates social inequalities, especially in neighborhoods lacking green space, adequate housing insulation, or access to cooling infrastructure.

Cities are beginning to confront these red zones through a range of adaptation and mitigation strategies. Urban greening initiatives, reflective surfaces, improved ventilation corridors, and heat-sensitive zoning policies are among the tools being deployed. Some cities have started to map urban heat vulnerability using sensor networks and thermal imaging to guide interventions more precisely. Others incorporate citizen data to identify overlooked hotspots or under-resourced areas. This includes the digital sphere in which red zones become visible as sites of contestation and negotiation as well.
In UDP3 we investigate where red zones can be located, delineated, and understood within the broader framework of urban risk policies and spatial justice. How and by whom are such zones delineated and negotiated? How do social patterns of inequality and power interests influence their formations? How are red zones made visible in planning and policy? What are the strategies of cities, economic actors, civic initatives, and inhabitants to deal with red zones? Who is most affected by them? And what role can urban design, technology, and citizen participation play in transforming red zones?

Using Hamburg as a primary context, we use case-based research to examine how cities and urban societies conceptualize and respond to red zones.