INTRODUCTIONWith ~76% of population residing in urban areas, Europe has a high urbanization rate, expected to grow further. Urban expansion challenges public health, particularly amid climate change. Green spaces mitigate these effects, benefiting physical and mental health and reducing mortality. OBJECTIVEThis study quantifies the impact of green space exposure on avoidable deaths at the census tract level in 2021 in an urban area of Tuscany, including Florence and seven neighbouring municipalities. The analysis focuses on medium/long-term effects, comparing actual exposure with counterfactual scenarios of increased greenery. METHODExposure was assessed using the 2015 average Normalized Difference Vegetation Index (NDVI) within 300m of each tract. Deaths in 2021 were estimated by redistributing municipality-level mortality data based on the tract-level demographics. Relative risks from literature adjusted for social deprivation. Mortality impacts were estimated for individuals aged over 35 years under three scenarios: (A) NDVI thresholds (0.5, 0.7, WHO-recommended), (B) +20% NDVI, and (C) +0.1 NDVI. The WHO threshold (25% green space) was converted to NDVI via a validated model. The exposure-response curve was estimated using a Bayesian replication of a recent meta-analysis. Uncertainty was accounted for via Monte Carlo simulations. RESULTSEstimated avoidable deaths: 335 [90% uncertainty interval: 0–785] for NDVI ≥0.5; 830 [0–1896] for NDVI ≥0.7. A +0.1 NDVI and +20% NDVI increase would save 305 [0–723] and 248 [0–585] deaths, respectively. The WHO threshold (NDVI = 0.33) suggests 54 avoidable deaths [0–128]. The central , with lower NDVI, showed the highest improvement potential. CONCLUSIONSDespite uncertainties, the impact is substantial. Urban forestry policies can mitigate avoidable deaths, highlighting the broader risks of green space scarcity. This approach can help public administrators recognize the value of investing in urban green spaces.