A health impact assessment of progress towards urban nature targets in the 96 C40 cities

Background

Urban greenspaces (eg, parks and trees) and blue spaces (eg, rivers and coasts) improve climate regulation and human health. In 2021, the mayors of 31 cities in the C40 Climate Leadership Group set 2030 targets for the percentage of urban greenspace and population with nearby natural (green or blue) space. We quantified annual all-cause mortality reductions from progress towards these targets for C40's 96 member cities.

Methods

We conducted a quantitative health impact assessment, testing three illustrative scenarios to increase urban greenspace: uniformly across space, in areas with the least nature, and in the most populated areas. We converted one percentage point progress towards each target in terms of the Normalized Difference Vegetation Index (NDVI) using previously published associations. We used mortality rate estimates from The Global Burden of Diseases, Injuries, and Risk Factors Study, population data from WorldPop, and a pooled hazard ratio of NDVI and all-cause mortality from an epidemiological meta-analysis.

Findings

Uniformly increasing greenspace by 1% yielded an estimated 96-city median of 1·77 (range 0·65–3·52, IQR 1·46–2·19) fewer annual premature deaths per 100 000 population; increasing the population percentage with nearby natural space yielded an estimated median of 0·56 (range 0·11–1·70, IQR 0·44–0·69) fewer annual premature deaths per 100 000 population. On average, compared with uniform increases, adding greenspace in the least natural areas provided 1·4–1·7 times (depending on the target) the health benefits, and adding greenspace in the most populated areas provided 2·7 times the health benefits.

Interpretation

The geographical distribution of greenspace expansion influences the magnitude of associated health benefits across varied urban contexts. Health benefits are largest when greenspace is added near population centres.