Quantifying the public health benefits of expanding natural spaces in urban areas

Abstract

Background and Aim: Access to greenspace (e.g. parks, trees) has been shown to improve physical and mental health by facilitating physical activity and social interaction as well as reducing stress, air pollution, and the urban heat island effect. While the health impacts of blue space (e.g. coastline, lakes, rivers) have been less studied, blue space is also hypothesized to provide similar health benefits through many of the same pathways. Here we assess the combined benefits of green and blue spaces, or natural space, for reducing all-cause mortality in approximately 100 cities worldwide that are members of the C40 Cities network. Methods: We use 2021 normalized difference vegetation index (NDVI) derived from the Landsat 8 satellite to identify urban natural spaces. We then use an epidemiologically-derived health impact function from a systematic review of the effects of greenspace on mortality along with WorldPop population estimates and Global Burden of Disease mortality rates from 2020 to quantify the health benefits of natural spaces in terms of reductions in all-cause mortality in each city. Results: Cities vary in their extent of natural space, including green and blue space individually, as well as the combined natural space metric. We estimate that these natural spaces reduced all-cause mortality in each city, and that variation in mortality benefits across cities is driven both by differences in natural space extent, as well as population and baseline mortality rates. Conclusions: Cities around the world experience different levels of natural spaces and associated health benefits. Expanding natural spaces to reduce carbon emissions and enhance urban sustainability and livability may further benefit local public health. Keywords: greenspace, blue space, natural space, NDVI