Based on scientific evidence, the World Health Organization advocates for public green space as an important component of healthy cities. Different pathways and mechanisms are likely to mediate the health effects of exposure to green spaces. Those range from stress reduction and increased physical activity to regulating ecosystem services, such as heat and noise reduction. Many of these pathways are causally related to common non-communicable diseases, for example, depression, and urban heat related morbidity, disorders that have been negatively associated with exposure to green spaces. The evidence is limited by various factors, such as lack of validation of exposure metrics and shortness of experimental data. Attempts to standardise and optimise exposure metrics are ongoing, but depending on what health outcome is studied different types of measurements are needed. For example, measuring the impact on heat related morbidity may require different metrics than for estimating mental health benefits. Aspects of green space exposure to be considered for measurement are availability, accessibility, qualities, and usage. Availability and accessibility can be determined for large-scale population studies and are often assessed through remote sensing data of various spatial resolution, sometimes combined with other data sources for mapping of land cover types, such as different tree species, of land use, such as recreational areas and sport facilities. Evaluating qualities of green spaces often requires field studies or qualitative analyses, resulting in smaller scale studies. Usage of natural spaces can be identified by big data collection, from sources such as accelerometers or smart phone applications. This presentation will provide an overview of the evidence on associations between urban green spaces and health, based on a systematic review of the literature. It will critically discuss existing exposure metrics and potential for validation and development.
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