Temporal variation in travel greenery across 86 cities in Europe

The positive impacts of urban greenery on human health and wellbeing are well documented in scholarly literature. The focus has mostly been on residential greenery or availability and access to recreational green spaces. The importance of greenery in travel environments has received much less attention. Furthermore, little consideration has been given to temporal dynamics, although research suggests that greenery benefits are not uniformly distributed over different seasons or daytimes. In this study, we aimed to fill these knowledge gaps by systematically assessing travel and residential greenery in 86 European cities. Moreover, we quantified the impact of seasonality and variation in daytime length by using an open data approach at the pan-European level. First, we compared travel and residential greenery using monthly NDVI composites derived from high-resolution Sentinel-2 satellite imagery. In addition, we explored the temporal dynamics of greenery and adjusted NDVI values accordingly. The results demonstrated that travel environments have significantly lower greenery levels than residential environments in European cities. Overall, we found a latitudinal gradient from low to high travel greenery in southern Europe compared to Nordic cities. The findings also indicated that accounting for temporal variations, especially in northeastern Europe, has significant impact on the measured availability of travel greenery. We conclude that travel environment greenery and temporal variations should not be overlooked in exposure studies because they can lead to a biased understanding of greenery availability and related spatial disparities. Our findings can therefore serve as a methodological and policy benchmark for greening goals in European cities.