An urban “green planning” approach utilizing the Weather Research and Forecasting (WRF) modeling system. A case study of Athens, Greece

The ameliorating thermal effect induced by green areas inside the warm urban microclimate of densely populated cities can improve the thermal comfort, as well as the overall health and living conditions of their inhabitants. In this modeling study, an effort is made to predict the impact of urban green solutions inside the high density and diverse urban landscape of the coastal city of Athens, Greece. The Weather Research and Forecasting (WRF) model, coupled to a single layer urban canopy model, is utilized to carry out high resolution (0.5 km) land use scenarios, focusing on proposed urban parks (sized 8 and 4 km2), which substitute a mainly industrial/commercial area (Eleonas) near the city's center. Results during nighttime of a typical warm-period day, depict a large cooling (on average greater than 5 °C) over the park's vegetated surface compared to current conditions, and a park cool island effect of 9.5 °C when comparing park and surrounding urban fabric air temperatures. Additionally, a significant cooling of the neighboring built-up areas is indicated at a radius proportional to the park's dimensions, related to the nocturnal advection of cool air beyond its borders (park breeze). During daytime, although no significant temperature changes over the park are simulated, a cooling (up to 1 °C) downwind its northern borders and over the inner city is predicted. This finding is related to the smaller frictional elements of the altered land cover located upon the axis of the seabreeze flow, which enhances the local sea-breeze circulation and its inland extent.

► A mesoscale model coupled with an urban canopy scheme can aid urban planning.
► Large scale green interventions considerably improve the microclimate of Athens.
► Landscape changes in the urban morphology influence local atmospheric flows.