by Y You, S Pan
Geophysical Research Letters 47(18): e2020GL0892862020
As of late May 2020, the Coronavirus Disease 2019 (COVID-19) had been found in over 200 countries and caused hundreds of thousands of deaths. Previous pandemics have largely been shaped by both physical and human geographical features. The authors note that urban vegetation could provide a place for people to carry out socially-distant activities and could also improve mental health. The study therefore aimed to Investigate the role of urban vegetation in slowing the spread of COVID-19 in the United States. Along with urban vegetation, three other factors were tested: population density, air temperature and baseline infection.
Using county level data, the effect of each individual factor on cumulative COVID-19 cases was explored using correlations. In the next step, a path analysis model (PAM) was used to explore the direct and indirect effects of the different variables and thus potential interactions. The first set of results showed that urban vegetation was significantly and negatively correlated with cumulative COVID cases: each 1% increase in the percentage of urban vegetation resulted in a 2.6% decrease in the cumulative COVID-19 cases. Both population density and baseline infection showed non-linear relationships, but the correlation between air temperature and cumulative cases was only weakly correlated. PAM results also showed that an increase in urban vegetation led to lower COVID-19 cumulative cases; however, population density showed the largest effect. Urban vegetation also has an indirect effect, through the other three factors, on cumulative COVID-19 cases. Although air temperature had a negative relationship with cumulative COVID-19, it was not statistically significant meaning an increase in temperature may not actually help slow or stop the spread of COVID-19.
The authors conclude that both baseline infections and population density will significantly affect the spread of COVID-19. However, urban vegetation could weaken this effect though a mediating function.