Putting a chill on the urban heat island effect

The urban heat island effect is a well-documented phenomenon that describes how concrete and asphalt surfaces in cities, combined with a lack of green space, absorb and reemit heat, increasing local temperatures, energy demand, and air pollution, especially impacting lower-income communities. With cities worldwide experiencing unprecedented summer heat, climate change has only exacerbated its impacts.

Ioannis Kokkinakis and Dimitris Drikakis examined the mitigating potential of urban greening, using computational fluid dynamics simulations and terrain-resolved topography, in the densely populated Greek capital city of Athens.

“A major urban greening project can cool the air… by about one degree Celsius on the hottest days — and the benefit does not stop at the park boundary; it can travel several kilometers downwind,” said Drikakis. “One degree is not trivial when a city is near heat-warning thresholds.”

Simulations showed replacing hotter surfaces with greener ones reduces the heat the ground reemits, and then wind distributes that change to other neighborhoods.

“That ‘downwind footprint’ is key: Greening can be a city-scale heat-mitigation lever when the wind is right,” said Drikakis.

The researchers credit computational fluid dynamics for illustrating how air flows around terrain and through urban corridors, how turbulence mixes heat, and how cooling spreads. They ran two matched scenarios — before and after greening — under identical meteorological conditions to isolate the effect of land-use change from the noise of “a different weather day.”

“For urban planning purposes, the message is, evaluate greening as a ‘footprint,’ not a dot on a map,” said Drikakis. “The benefits are spatially uneven and transported by wind, so who gains depends on street layout, terrain, and prevailing flow.”

Source: “Flow and heat transport effects from urban greening in a metropolitan environment,” by Ioannis William Kokkinakis and Dimitris Drikakis, Physics of Fluids (2026). The article can be accessed at: https://doi.org/10.1063/5.0305372 .