Flow and heat transport effects from urban greening in a metropolitan environment

Urban heat islands exacerbate thermal stress in dense cities, where limited green spaces intensify microclimate extremes. This study examines the impact of urban greening on urban flow and thermal fields, using the densely populated city of Athens, the capital of Greece, as a case study. The study utilizes high-resolution computational fluid dynamics simulations. Employing terrain-resolved topography and land-use indices, we investigated and compared the effects of urban greening in densely populated areas. Urban flow and thermal fields are compared between the two case scenarios under identical meteorological forcing. Large-eddy simulations indicate that the redeveloped landscape will reduce near-surface mean air temperatures by almost 1 °C on hot summer days, with the effect extending further downstream during moderate prevailing south winds. The cooling effect extends for several kilometers downstream, but at a gradually decreasing rate as the cooled air begins to warm again due to the dense urban landscape. Translated into operational terms, a reduction of 1 °C on a hot day near city-specific thresholds corresponds to approximately 3% lower heat-related mortality risk, reduced time in higher universal thermal climate index heatstress categories, and approximately 2.6% peak-demand relief for the Greek electricity system. These results establish the microclimatic, public health, and energy-relief relevance of single-degree cooling from urban greening, while highlighting the spatial heterogeneity that current synoptic stations underdetect, motivating denser urban monitoring to further evaluate this phenomenon. The above co-benefits, along with the improved ventilation shown by the computational fluid dynamics study, establish 1 °C as a policy-relevant microclimate gain rather than a trivial fluctuation.