New Publication | Urban Forestry & Urban Greening
How does Hamburg's urban vegetation cope with hot, dry summers?
As climate change brings more frequent and intense compound heat and drought events to Northern Europe, understanding how urban green spaces respond is increasingly important for city planners and ecologists alike. A new study by Nadine Kaul, Nikola Lenzewski, Olaf Conrad, Jürgen Böhner, Kai Jensen, and Benjamin Poschlod (TUHH, IGWS) — published in Urban Forestry & Urban Greening provides one of the first systematic, high-resolution assessments of drought impacts on urban vegetation in a Northern European city. Using satellite imagery from the European Space Agency's Sentinel-2 mission, the team tracked how over 13,000 mapped vegetation patches across Hamburg changed in greenness during the three recent compound hot and dry summers of 2018, 2020, and 2022. By combining these observations with a widely used drought index (the SPEI), they were able to identify which vegetation types showed signs of stress — and which did not.
The results reveal a striking divide between herbaceous and woody vegetation. Grasslands, heathlands, and parks lost measurable greenness during drought summers, with the strongest declines on already dry sites and in the exceptionally severe summer of 2018. Forests and shrublands, by contrast, showed no such short-term decline — likely because their deeper root systems allow them to access soil moisture that short-term meteorological droughts do not reach. Crucially, the study also shows that even within the same vegetation type, individual patches responded very differently depending on local site conditions such as groundwater depth, soil type, and elevation. This fine-scale variability, the authors argue, can only be detected using high-resolution data — broad regional analyses would miss it entirely. The findings have direct practical relevance: the greenness of herbaceous vegetation can serve as a low-cost, satellite-derived monitoring of near-surface soil moisture across the city, helping to identify where urban green spaces are most at risk during drought — and where cooling functions may fail precisely when they are needed most.
Read the full open-access article: Kaul et al. (2026): Remote sensing reveals heterogeneous responses of urban vegetation types to compound heat and drought events in Hamburg, Germany. Urban Forestry & Urban Greening 122, 129489. https://doi.org/10.1016/j.ufug.2026.129489
