Cost-effectiveness of blue-green infrastructure strategies for urban heat mitigation

Urban heat stress is intensifying under climate change, challenging cities to identify mitigation strategies that are not only effective but also economically viable over long planning periods. Blue Green Infrastructures (BGI), such as trees, bioretention cells, porous pavement, ponds, have been increasingly promoted as a key measure to mitigate heat stress. While some studies have assessed the cooling potential of individual BGI interventions, the effects of combining these elements and their long-term cost-effectiveness under future climates have not yet been thoroughly evaluated. The goal of this study is to evaluate which urban heat mitigation strategies provide the greatest thermal benefits per unit cost over their lifetime.

To do so, we used a microclimate model (UT&C) to simulate Universal Thermal Climatic Index (UTCI) within 3 standardized urban canyons across three Swiss cities (Zurich, Geneva, and Lugano). Simulations are conducted for three decadal periods corresponding to present-day conditions (2015–2025, observations), mid-century (2050), and late-century (2080) climates, derived from the convection-permitting COSMO-CLM regional climate model and bias-corrected to the station scale. Across four baseline scenarios characterized by different vegetation quantity and quality, we implement a set of single and combined BGI and management scenarios that vary tree coverage, ground vegetation coverage, vegetation species selection, bioretention cells, porous pavements, ponds, and irrigation strategies. Model outputs of thermal comfort are integrated with cost data from the literature to compute cost-effectiveness metrics.

Preliminary results for Zurich indicate that eight individual interventions reduce the median UTCI by -0.1–1.2 °C across the baseline scenarios under current climate conditions. Increased tree coverage consistently shows the strongest cooling performance, particularly under low-vegetation baseline conditions. Future work will assess combined intervention scenarios and their lifetime cost-effectiveness. Overall, this work provides insights for prioritizing urban heat mitigation strategies by jointly considering thermal performance and economic efficiency under climate change.