A one-way coupled mesoscale–urban dispersion model as effective tool to investigate heatwave and urban greening impacts

Heatwaves are expected to intensify in frequency, duration, and magnitude under climate change, exacerbating thermal stress and air pollution in urban areas. This study presents a scalable mesoscale-urban modeling framework designed to analyze the impacts of heatwaves on meteorology and air quality and to evaluate the effectiveness of urban greening strategies in mitigating these impacts during extreme heat events. The modeling chain couples the WRF mesoscale model with the ADMS-Urban dispersion model and is applied to Rome (Italy) to simulate a prolonged heatwave in July 2022, together with the preceding and following periods. This enables comparative analysis across pre-heatwave, heatwave, and post-heatwave phases. Results show that heatwave conditions increased near-surface air temperature by approximately 2 degrees C and reduced wind speed by 1-2 m s-1, while wind direction remained largely unchanged. These meteorological changes led to higher in-situ pollutant concentrations, particularly tropospheric ozone, with spatial pollution patterns largely preserved. Two urban greening scenarios-characterized by moderate and substantial increases in urban green fraction-were then investigated. Both scenarios resulted in widespread cooling and enhanced ventilation across the study area, improving thermal comfort, especially during heatwave conditions. These benefits also translated into overall reductions in ozone concentrations, despite spatially heterogeneous responses driven by non-linear photochemical processes. Although based on a single case study, the results highlight the potential of the proposed framework as a robust tool to support climate-resilient urban planning and inform evidence-based adaptation strategies aimed at mitigating the combined impacts of heatwaves and air pollution in cities.