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

Sammanfattning

Urban environments often experience higher temperatures compared with their ruralsurroundings due to the effect of urban heat islands (UHI). As the climate changes and thefrequency and intensity of heatwaves increase, urban vegetation is often proposed as anadaptation strategy for urban microclimates. Through shading and evapotranspiration,vegetation can help regulate temperatures and thermal comfort. However, these mechanismsbecome less effective when vegetation health gets decreased, often occurring during stressfulweather conditions such as heatwaves. While the cooling effect of vegetation is well knownwithin the field of urban climatology, how different vegetation combinations and structuresrespond to heatwaves is less studied.By using remote sensing, this study investigates how different vegetation structures respondedto 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 VegetationIndex (NDVI) has been used as an indicator for vegetation activity and vitality. Focus lies onhow different vegetation structures and urban environmental factors contribute to maintainingvegetation health under drought- and heat stress conditions compared to a historical baselineincluding the years 2017 & 2019-2025. The four vegetation structures that were analysed areas follows: ‘Grass’, ‘Grass & Trees’, ‘Trees’ and ‘Street Trees’. The urban environmentalfactors were analysed through the independent variables Soil type, Vegetation fraction, andElevation above sea level.The study shows that vegetation resistance to vegetation stress during heatwaves variesdepending on vegetation type and urban context. ‘Trees’ and ‘Grass & Trees’ showed tomaintain vegetation health to a larger degree compared to ‘Grass’ and ‘Street Trees’. The resultsunderline the importance of trees and more complex vegetation structures in climate adaptationstrategies revolving urban environments, especially with extreme heat events in mind where thecooling function of vegetation is most important. Additionally, Soil type showed to be the factoraffecting vegetation the most during the heatwave of 2018 with coarser soils correlating withlower NDVI compared with finer soils.