On the cooling potential of urban heating mitigation technologies in a coastal temperate city

We assess the impact of advanced heat-mitigation technologies in a coastal temperate city under heatwave conditions. For the first time urban-heating mitigation scenarios that refer to 'cool/reflective' roofs and roads, 'green/living' roofs and shading by replacing low urban vegetation with deciduous broadleaf trees are considered at the highly dense-populated city of Athens (Greece). Numerical simulations are performed for a typical seebreeze and a heatwave day with the Weather Research and Forecasting (WRF) model coupled to an urbancanopy model. Highresolution data on vegetation and urban land use, derived from satellite image analysis, are considered. All scenarios show a cooling effect, with the maximum mean daytime temperature reduction in the case of 'cool/reflective' roofs and roads. During daytime, the mean ambient-temperature reduction reaches up to 1 degrees C while for the surface-temperature up to 9.5 degrees C and 11.5 degrees C, on the see-breeze and heatwave day respectively. In the case of 'green/living' roofs, the mean daytime latent-heat flux is increased (e.g. up to 140 W/ m2 on the heatwave day) due to increased evapotranspiration while the surface temperature is more affected during nighttime. Both scenarios result in a sea-breeze attenuation of 0.5-1 m/s. The presence of deciduous broadleaf street trees has a minor impact on mean ambient temperature but an evident reduction in surface temperature. The mean urban-heating reduction ranges from 0.1 degrees C to 0.8 degrees C and from 0.3 degrees C to 1.7 degrees C during the sea breeze and heatwave day respectively, with the maximum reduction shown in 'cool/reflective' roofs and roads and the minimum in 'shading trees' scenarios.

Automated summary

This study assesses the impact of advanced heat-mitigation technologies in the coastal temperate city of Athens during heatwave conditions. Different mitigation scenarios lead to varying effects on ambient and surface temperatures, with 'cool/reflective' roofs and roads showing the most significant cooling effect.