Analysis of dynamics and forecast potential of rapid desiccation events and their impacts on urban vegetation

• Applicant: Professorin Dr. Eva Nora Paton
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560467964

To mitigate the effects of water deficit on urban vegetation, it is essential to understand not only long-term drought impacts, but also the potentially even more hazardous effects of flash droughts. In this project, we want to gain an in-depth understanding of the under-researched dynamics of rapid desiccation events resulting from exceptionally high evaporative demand and of their impacts on urban green. We define rapid desiccation as the process of extreme drying that occurs during relatively short periods of 5–30 days due to particularly high evapotranspiration. Our aim is to identify, quantify, and predict the onset, velocity, trajectories, and impacts of rapid desiccation events (RDEs) on urban green spaces and street trees in the highly sealed city centre of Berlin, both of which provide important ecosystem services, including heat mitigation, stormwater retention, and recreation. To achieve this aim, experimental studies on urban grass plots and street trees will be conducted to elucidate the temporal dynamics of variables describing the ecohydrological and physical boundary conditions before, during and after RDEs. The experimental studies will allow the detection of moisture changes over the entire trajectory of desiccation, including the identification of inhibiting and enhancing factors and resulting vegetation response in order to assess grass and tree vitality. To apply the derived process knowledge to larger temporal (up to decades) and spatial scales (same tree species up to district scale; grassland plots up to multiple urban park areas), we aim to develop and validate modelling tools for moisture levels that reproduce the rapid desiccation dynamics. Finally, reliability analysis will be performed using hindcast climate data from the last 30 years and a confusion matrix to assess whether 10-day weather predictions for evaporative demand and water availability can be used to successfully predict the onset, termination, and impact of RDEs. The proposed monitoring and modelling analysis of rapid desiccation events will enable joint evaluation and spatial scaling of how quickly and how dry the urban surface may become under different (and changing!) stress periods. The project will: i) address the extent to which rapid desiccation events during periods of excessive evaporative demand affect urban vegetation (trees versus green spaces), taking into account different urban site conditions; ii) evaluate the magnitude and severity of impact and the synchronicity of rapid desiccation events in relation to long-term water deficit phases relevant to planning mitigation measures for urban vegetation; and iii) assess the reliability of 1-day to 10-day forecasts for determining the onset and development of rapid desiccation events. To this end, a robust process description and successful method for forecasting RDEs will enable a timely response to the emerging need for innovative tools that can deal with novel forms of drought.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigator: Professor Dr. Boris Schröder-Esselbach
• Cooperation Partner: Professor Dr. Thomas Ford