From countering the impact of pollution to better mental health, the presence of greenery in and around people’s places of residence has multiple health benefits. A new 3-30-300 thumb rule has quantified the amount of vegetation needed to boost public health. Research Centre ISGlobal conducted a study in Barcelona, Spain, to evaluate the association between the green space rule and mental health. Results suggest that strict adherence to the rule is clearly associated with improved mental health. The research team behind the study has spoken of further need for similar studies in different cities.
This urban greening rule states that every citizen should be able to see at least three trees from their residence, have at least 30 percent tree canopy cover in their vicinity, and live within 300 metres from the nearest park or similar green space. Urban forester Cecil Konijnendijk first proposed the rule. It has since received widespread support from people in similar professions.
The cross-sectional study evaluating the rule was based on a sample of 3145 individuals between the ages of 15 and 97. The team created 3-30-300 green space indicators using remote sensing, land cover maps, and questionnaire data. They assessed the participants’ mental health status via the 12-item General Health Questionnaire (GHQ-12). The use of sedatives or antidepressants and visits to a psychiatrist or psychologist were also taken as mental health indicators.
The study found that only 4.7 percent of those surveyed fully met the 3-30-300 criteria. A little over 43 percent of respondents had a minimum of three trees within 15 metres of their house, while 62.1 percent had a major green space within 300 metres. Only 8.7 percent of the people lived in an area with adequate surrounding greenness. However, close to 22.4 percent of the surveyed population had none of these elements.
The study findings indicate that complete adherence to the 3-30-300 green space rule was linked with better mental health. In addition, it was also associated with fewer visits to a psychologist and less medication use.
According to ANI, Mark J. Nieuwenhuijsen, the lead author of the study, said that there is an immediate need to supply citizens with more green space. “We may need to tear out asphalt and plant more trees, which would not only improve health, but also reduce heat island effects and contribute to carbon capture." Nieuwenhuijsen further said that any initiative that results in a greener city would be a step ahead. “The key message is that we need more and faster greening", the lead author said.
The research team is of the view that similar studies should be carried out in cities with more tree cover than Barcelona, given that the lack of green space here has limited the ability to assess the 30 percent aspect of the urban greening rule.
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