Quantifying Urban Nature and the Associated Health Benefits Across Global Cities Using High-resolution Satellite Imagery
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0.270, range
0.63, 3.44) annual premature deaths per 100,000 could be averted. Increasing the population percentage with nearby green or blue space by 1%, mirroring the second target, was associated with a median of 0.55 (range
Epidemiologic literature links urban green (e.g. parks, tree-lined streets) and blue (e.g. coasts, rivers) space to improved mental and physical health. Increasingly, cities are expanding urban nature for its health and climate resiliency benefits. Despite interest in urban nature interventions, gaps remain in measuring nature exposure and linking policy goals to expected health benefits. Methods
0.11, 1.66) fewer annual deaths per 100,000. Adding greenspace in areas with the least amount of nature and the greatest density of population provide 1.4-1.7 times (depending on the target) and 2.7 times the health gains of uniform increases, respectively. We observed large variation in greenest-season NDVI across cities (mean
0.148, 0.739). We found that approximately 80% of C40 cities already meet at least one target, and almost 50% meet both. After converting the C40 2030 urban nature targets to the NDVI scale, we quantified the potential reductions in mortality associated with incremental progress towards the two C40 targets. We found that if cities were to increase greenspace uniformly across their urban extents by 1%, in accordance with the first C40 target, a median of 1.74 (range
This work addresses the lack of interoperability between the health literature and urban nature policies by providing a framework for measuring urban nature targets on the NDVI scale. We use these translations to quantify the health benefits of expanding urban greenspace across a global set of cities. We find that where urban greenspace is added has important implications for the magnitude of the associated health benefits. Adding greenspace near population centers provides the greatest health impact. We found substantial inter-annual variation in greenest-season NDVI which would suggest that efforts to increase urban nature may be partially masked or exaggerated by climate patterns. Our work supports existing literature in finding that increasing urban greenspace can be beneficial to human health and highlights the limitations of NDVI as a measure for capturing the effect of urban greenspace interventions.
We found that global cities vary greatly in their extent, distribution, and type of urban nature. We estimated a mean greenest pixel NDVI across the 96 C40 cities of 0.538 (range
We used high-resolution satellite imagery from the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA), accessed through Google Earth Engine, to quantify urban nature across a global set of cities. We first addressed the incompatibility between scientific measures and real-world policies by quantifying the 2020 urban nature extent and distribution across the 96 C40 Climate Leadership Cities and their 2030 urban nature targets in terms of the normalized difference vegetation index (NDVI). Next, we estimated the associated health benefits of incremental progress towards these targets across the 96 cities, by combining our exposure metrics with baseline mortality data from the Global Burden of Disease study and gridded population data. Finally, we assessed urban nature levels across 1,041 global cities from 2014 to 2023, and estimated changes in mortality associated with changes in NDVI over time. Results
0.072, 0.580), related to region and climate classification. While globally, city greenspace has remained relatively constant from 2014-18 to 2019-23, it has changed by over 20% in individual cities. We estimated that on average, across 1,041 global cities, changes in NDVI over these two periods were associated with 5.04 (95% CI
4.64, 5.19) additional deaths per 100,000 annually, ranging from 569.84 fewer to 521.82 more deaths per 100,000 across cities. Discussion
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Martin_gwu_0075A_17179.pdf | 2025-07-20 | Open Access |
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Chapter_2_Appendices.pdf | 2025-07-20 | Open Access |
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Chapter_3_Appendices.pdf | 2025-07-20 | Open Access |
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Chapter_4_Appendices.pdf | 2025-07-20 | Open Access |
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