Urban green infrastructure and depression dynamics: a causal loop analysis

Major depressive disorder affects an estimated 280 million people worldwide and ranks among the leading contributors to years lived with disability. Single-cause explanations are insufficient to account for the complexity of depression, which is shaped by dynamic interactions between biological, psychological, social and environmental determinants. Urban environments, where over half of the global population currently lives and projections suggest this will reach nearly 68% by 2050, concentrates multiple interacting stressors including air pollution, noise, heat island effect, social fragmentation, and diminished access to restorative environments that trigger and reinforce pathways associated with depression onset and persistence.

This study aims to design a causal loop diagram (CLD) that integrates depression-generative mechanisms with the ways urban green infrastructure can counteract these processes, serving both as analytical framework and boundary object for transdisciplinary dialogue at the interface of urban ecosystems and mental health.

The methodological approach builds upon foundational CLDs from Wittenborn et al. and Herrera et al. that model depression as interacting feedbacks across cognitive and biological processes. We adapted these frameworks to the urban context by identifying mechanisms relevant to city environments and by systematically incorporating urban environmental variables alongside nature-related factors, informed by scientific literature. The resulting CLD will undergo validation through focus groups with stakeholders from health, planning, ecology and policy sectors to ensure relevance and plausibility.

The CLD identifies three dominant reinforcing feedbacks that may drive urban depression dynamics: a stress sensitization cycle in which chronic exposure to noise, air pollution, heat, and artificial light amplifies physiological stress responses, progressively lowering stress tolerance; a behavioural withdrawal loop in which depressive symptoms reduce physical activity and social engagement, deepening isolation and symptom severity; and a sleep disruption loop in which environmental disturbances impair sleep quality, increasing vulnerability to stress and mood dysregulation.

Counteracting these dynamics, the CLD highlights three principle balancing feedbacks associated with urban green infrastructure. An environmental mitigation loop links vegetation and tree canopy to reduced air pollution, noise, and ambient temperatures, weakening stress-generative processes. A restoration loop captures how accessible, high-quality green spaces promote psychophysiological restoration, physical activity, and informal social interaction, countering behavioural withdrawal. A sleep-supporting loop reflects the capacity of vegetated environments to moderate nighttime temperatures and noise, improving sleep quality and reducing stress sensitivity.

Analysis of these feedback loops reveals strategic intervention points, including increasing green infrastructure coverage and quality, reducing access barriers, and ensuring equitable distribution so protective loops operate across socioeconomic groups.

This work provides a systems level framework for understanding the dynamic of urban depression and for identifying intervention strategies that directly support Sustainable Development Goals 3, 11, 13 and 15, demonstrating that mental health promotion in cities requires both targeted environmental improvements and structured cross-sector collaboration grounded in systems thinking.