A health impact assessment of changes in NDVI on all-cause mortality across 1041 global cities

Abstract Urban greenspaces are associated with improved health and climate resiliency. Large scale health impact assessments of urban greenspace and mortality have been limited to American and European cities. We estimated changes in mortality associated with observed differences in population-weighted greenest season normalized difference vegetation index (NDVI) between 2014–2018 and 2019–2023 across 1041 global cities representing 174 countries. We used publicly available high-resolution satellite-derived estimates of NDVI and population, baseline disease rates from the Global Burden of Disease study, and a hazard ratio of the association between NDVI and all-cause mortality from an epidemiological meta-analysis. We found that urban greenspace varies substantially across cities (NDVI mean: 0.270, range: 0.072, 0.580) and by climate classification and geographic region. Despite modest global average changes in NDVI from 2014–2018 to 2019–2023, NDVI has changed by over ±20% in individual cities. Median regional changes were largest in South-eastern Asia (−0.022), Sub-Saharan Africa (−0.010) and Eastern Asia (+0.014) and most stable in arid climates (<0.000). These changes were associated with a global mean of 0.19 (95% CI: 0.12, 0.27) additional annual deaths per 100 000 in the 2020 population, ranging from 24.44 fewer to 21.84 more deaths per 100 000 across cities. Health impact assessments of NDVI and all-cause mortality have largely been conducted in European and North American cities, where we found NDVI was generally higher and more stable. Our results highlight large heterogeneity in urban greenspace extent and variability across global cities and the importance of characterizing the relationship between health and NDVI in more diverse contexts.