An urban green space intervention with benefits for mental health: A health impact assessment of the Barcelona "Eixos Verds" Plan

Background: Mental health disorders account for over 30% of the global burden of disease. There is a positive association between green space exposure and better mental health, and therefore urban greening can be an effective public health tool. Barcelona is a compact city with one of the highest population and traffic densities in Europe, with limited green spaces. Under the umbrella of the Superblock model, the Barcelona City council is implementing the Eixos Verds Plan for extensive street greening. We estimated the potential mental health benefits of this plan.Methods: We performed a quantitative health impact assessment at the Barcelona grid-cell level (n = 1,096). We compared the baseline green space situation (2015) with the proposed plan and translated the increase in green space into a) percentage of green area (%GA) and b) NDVI. We combined exposure data with Barcelona-specific mental health risk estimates, adult population (n = 1,235,375), and mental health data, and calculated pre-ventable cases.Findings: Under the Eixos Verds Plan, we estimated an average increase of 5.67 %GA (range: 0.00% -15.77%) and 0.059 NDVI (range: 0.000 -0.312). We estimated that with the Eixos Verds Plan implementation, 31,353 (95%CI: 18,126-42,882) cases of self-perceived poor mental health (14.03% of total), 16,800 (95%CI: 6828-25,700) visits to mental health specialists (13.37% of total), 13,375 (95%CI: 6107-19,184) cases of an-tidepressant use (13.37% of total), and 9476 (95%CI: 802-16,391) cases of tranquilliser/ sedative use (8.11% of total) could be prevented annually, along corresponding to over 45 M euro annual savings in mental health costs annually. Interpretation: Our results highlight the importance of urban greening as a public health tool to improve mental health in cities. Similar results for green interventions in other cities could be expected.