The impact of green space on mental health
Using Covid-19 quarantines as quasi-experimental interventions, Lee, Mai and Park (2023) investigate the impact of green space on mental health amid mobility restrictions.
Wong Wei Chen
11 December 2023
Imagine not being able to drink at your regular pub or eat at your favourite restaurant for an entire month. For that matter, imagine not being able to do much of anything else. Cabin fever could drive people up the wall – especially those who love the great outdoors.
Numerous studies on physical and social isolation – such as those arising from Covid-19 lockdowns and other quarantine measures – have discovered an adverse effect of such restrictions on mental health.
On the other hand, research in environmental psychology has documented positive associations between exposure to green space and overall wellbeing. After lockdowns were imposed during early pandemic days, Google searches for “go for a walk” increased significantly.
In their paper “Green space accessibility helps buffer declined mental health during the COVID-19 pandemic: evidence from big data in the United Kingdom”, Lee, Mai and Park (2023) contribute to the literature by investigating big data of mobile phone users in London, in particular focusing on people who travelled to green space i.e. “green-space travellers”.
The travel behaviours of 2 million mobile phone users in London furnished sufficient data volume for a robust empirical investigation, while the 2-year long longitudinal study furnished both a benchmark period (Jan 2019 – early 2020) and a treatment period i.e. from the first Covid-19 outbreak in early 2020 to Jan 2021. Multiple outbreak and lockdown periods over the course of the pandemic represented multiple instances of natural quasi-experimental intervention in the form of mobility restrictions.
Using a validated mental health scale (the General Health Questionnaire), the researchers also measured the impact of Covid-19 mobility restrictions on mental health.
Overview of methodology
Using a Geographic Information System, Lee et al. found that, following an outbreak or lockdown, the behavioural trends of green travellers changed significantly after an 800m threshold radius from green spaces such as parks and gardens. The 800m cut-off also coincided with a walkable distance in the existing literature.
The treatment group thus comprised residents who lived within 800m of green space, while the control group were those who lived beyond this perimeter. The pandemic induced mobility restrictions represented exogenous shocks administered in quasi-experimental fashion to both groups over the course of the longitudinal study.
Findings
After Covid-19 outbreak in early 2020, the total number of travellers within London significantly decreased by 25%, and the most significant drop of 55% was seen when the first lockdown was imposed. While overall numbers dipped, residential neighbourhoods within 800m of the nearest green space revealed a reverse trend.
In treatment neighbourhoods during the benchmark period in 2019, the pre-existing proportion of green-space travellers – defined as the ratio of green-space travellers to total travellers – was 1.4 percentage points higher than those in the control group (i.e. >800m from green space). Following Covid outbreak, the difference was amplified to 1.6 percentage points, thereby suggesting that residents in treatment neighbourhoods had a higher tendency to visit green spaces, even as the total travel volume dropped amid quarantine restrictions.
As a robustness test, the researchers compared neighbourhoods with similar characteristics (i.e. with controls for various demographic and socioeconomic attributes), and again found the “distance away from green space” parameter to have a similar effect on travel behaviours. By minimising the potential confounding effects of demographic and socioeconomic variables, the effect of the distance parameter could be better isolated – thereby furnishing stronger evidence that distance from green spaces exerted a causative effect on travel behaviours.
The proportion of green-space travellers in treatment neighbourhoods was approximately 0.9 percentage points higher compared with other London neighbourhoods with similar characteristics but located farther from green spaces.
During lockdown periods, treatment neighbourhoods experienced an additional increase of 0.5 percentage points in the proportion of green-space travellers. Given that the average proportion of green-space travellers in London was 4.2%, the total increase of 1.4 percentage points during lockdown periods was significant.
The results suggested that green space accessibility played an even more important role in travel to green spaces when people were facing strict restrictions on mobility. In the context of Lee et al.’s study, an 800m radius appeared to be the threshold distance, after which green space travel followed a similar downward trajectory as overall travel volume.
Impact on mental health
The researchers next investigated the relationship between proximity to green space and mental health. Using data from the UK Household Longitudinal Study (UKHLS) – which includes the General Health Questionnaire for mental health – Lee et al. conducted one-to-one matching of individuals via a propensity score matching procedure. About 2,500 individuals residing within 800m from green space were paired with a highly similar counterpart living outside the threshold distance. Matched pairs were highly homogeneous with respect to age, race, family composition, earnings and drinking/smoking habits.
Findings revealed that, following lockdowns, individuals who lived close to green spaces saw a much smaller increase in the distress score than those who lived farther away. Given that matched pairs were highly similar, the divergence in mental wellbeing could be attributed to proximity to green space.
Policy implications
Unlike prior studies which studied mental wellbeing in terms of individual characteristics – such as gender, age, education, ethnicity and socioeconomic position – Lee at al.’s study attempts to explain mental health in terms of environmental factors, namely proximity to green spaces. In so far as the environment is a determinant of mental health, opportunities arise for policymakers to intervene in terms of urban planning and placemaking.
The study also highlighted the elevated vulnerability of those who were deprived of access to green space during quarantine periods, and thus sends a clear signal to pay more attention to this subsegment of the population, especially during periods of restricted mobility. Beyond economic inequality, unequal access to public spaces – whether arising from distance and other geographical barriers or entrenched social patterns – becomes more salient as an urgent issue that needs to be addressed alongside the distribution of wealth in society.
LEE, Kwan Ok is associate professor and Dean's Chair of Urban Planning at the Business School of the National University of Singapore (NUS). She is also the Deputy Head in the NUS Department of Real Estate.
MAI, Ke Michael is an assistant professor in the Management & Organisation Department of the NUS Business School.
PARK, Souneil is a researcher in computational social science, Telefónica Research in Barcelona.