VEGETATION RESPONSE TO THE 2018 HEATWAVE IN INTRA-URBAN ENVIRONMENTS: AN ANALYSIS OF NDVI, VEGETATION STRUCTURE, AND ENVIRONMENTAL FACTORS IN GOTHENBURG, SWEDEN

Abstract

Urban environments often experience higher temperatures compared with their rural surroundings due to the effect of urban heat islands (UHI). As the climate changes and the frequency and intensity of heatwaves increase, urban vegetation is often proposed as an adaptation strategy for urban microclimates. Through shading and evapotranspiration, vegetation can help regulate temperatures and thermal comfort. However, these mechanisms become less effective when vegetation health gets decreased, often occurring during stressful weather conditions such as heatwaves. While the cooling effect of vegetation is well known within the field of urban climatology, how different vegetation combinations and structures respond to heatwaves is less studied. By using remote sensing, this study investigates how different vegetation structures responded to the heatwave during the summer of 2018 within the intra-urban environment of Gothenburg, Sweden. The analysis is based on Sentinel-2 (L2A) data from the Copernicus program, normalised through Pseudo Invariant Features (PIF). The Normalised Difference Vegetation Index (NDVI) has been used as an indicator for vegetation activity and vitality. Focus lies on how different vegetation structures and urban environmental factors contribute to maintaining vegetation health under drought- and heat stress conditions compared to a historical baseline including the years 2017 & 2019-2025. The four vegetation structures that were analysed are as follows: ‘Grass’, ‘Grass & Trees’, ‘Trees’ and ‘Street Trees’. The urban environmental factors were analysed through the independent variables Soil type, Vegetation fraction, and Elevation above sea level. The study shows that vegetation resistance to vegetation stress during heatwaves varies depending on vegetation type and urban context. ‘Trees’ and ‘Grass & Trees’ showed to maintain vegetation health to a larger degree compared to ‘Grass’ and ‘Street Trees’. The results underline the importance of trees and more complex vegetation structures in climate adaptation strategies revolving urban environments, especially with extreme heat events in mind where the cooling function of vegetation is most important. Additionally, Soil type showed to be the factor affecting vegetation the most during the heatwave of 2018 with coarser soils correlating with lower NDVI compared with finer soils.