Integrating Storyline-Based Warming Framework with Urban Climate Modeling: Assessing Green Infrastructure Cooling During Extreme Heatwaves

Urban areas are vulnerable to extreme heat events, a vulnerability that is intensified by climate change. Although many studies have examined heat mitigation strategies using observational or reanalysis data, there have been few explicit assessments of future climate conditions at an urban scale. From a climate modelling perspective, the storyline approach provides a consistent physical framework for evaluating event-specific responses to warming. Its application, however, in urban contexts has been constrained by the coarse resolution of regional climate models at this scale. This study addresses this gap by analyzing the June 2019 European summer heatwave in Karlsruhe, Germany, using an urban climate model. A 3 km resolution ICON regional climate model, which is driven by global storylines from the AWI-CM1 model, provides input for high-resolution urban climate simulations. Two scenarios are considered: (i) the present-day heatwave, and (ii) a future warming storyline. Each includes a baseline and an adaptation configuration featuring enhanced urban green infrastructure (e.g. green roofs). Urban-scale simulations are performed using the Parallelized Large-Eddy Simulation Model with urban parametrization (PALM-4U). This employs a 20 m parent domain and a nested 5 m child domain in order to explicitly resolve urban morphology, land–atmosphere interactions and vegetation processes. Thermal comfort indices, including the Universal Thermal Climate Index (UTCI) and Physiological Equivalent Temperature (PET), are calculated to evaluate the impact of the heatwave on thermal comfort and the effectiveness of green infrastructure interventions in current and future conditions. Our findings aim to demonstrate the added value of combining warming frameworks based on storylines with urban-scale modelling for event attribution and climate-resilient urban planning. The results provide actionable insights into the potential of increased green spaces to mitigate heat stress during extreme heatwaves in the present and future.

These simulations are part of the research project “climate Adaptation sCenarios To redUce the impActs of exTreme Events” (ACTUATE).