Identifying urban vegetation stress factors based on open access remote sensing imagery and field observations

Abstract Healthy vegetation in cities provides ecosystem services, which contribute to the overall well-being of urban populations, especially in times of climate change and increasing urbanization. More specifically, vegetation monitoring is needed in the context of intensifying and mitigating factors of the Urban Heat Island (UHI) effect. Therefore, fast and low-cost, but reliable approaches are needed for monitoring the status of urban greening. A satellite-based monitoring scheme based on freely available data could ensure the provision of key urban ecosystem services, and guide both policy maker and practitioners. Thus, the main objective of this paper is to investigate the impact of urbanization and urban green management on vegetation status of park trees during summer season in Bucharest, the capital city of Romania, using remote sensing. This city is known to be affected by air pollution and the UHI effect. Further, it is an example of a city with limited green spaces compared to other European cities. Hence, spatial data on vegetation status and potential impacts as a basis for management schemes are required to maintain a healthy urban green infrastructure. Vegetation indices related to chlorophyll, senescence, greenness and water stress were calculated from Sentinel-2 imagery as response variables to vegetation stress. Vegetation status was then predicted for each park using spatial environment factors (e.g. presence of irrigation systems) in a mixed model approach to account for heterogeneity among parks. The most important predictors of vegetation stress were irrigation systems, land surface temperature, distance to a lake and proximity to roads. However, the effect of these predictors on the vegetation status differed among parks. Therefore, a mixed effect model approach is suggested to quantify the effects of urbanization on green spaces in cities, and there is a high potential to use freely available satellite data for a spaceborne-monitoring service of urban green infrastructure.