Simulating the Cooling Potential of Tilia Trees in Berlin Using PALM-LES: The Impact of Tree Age and Density During a Heatwave

This study investigates the relationship between tree age, density, and their cooling effect on the urban canopy layer (UCL) and human thermal comfort at the microscale during a heatwave in Berlin. An empirical tree growth model based on Lalic and Mihailovic (2004) is used to derive leaf area density (LAD) profiles for Tilia trees at various ages. The Larsen and Kristoffersen (2002) tree database of 331 Tilia trees is employed to establish the physiological tree dimensions based on the empirical relationship between tree growth and total leaf area. The PALM canopy generator is used to configure age-specific LAD profiles at a 1m grid resolution for 48 scenarios, varying tree age (10-80 years) and stem-to-stem density (10-35m). The study simulates an extreme heatwave event using PALM in LES mode.

The results are expected to show a linear correlation between tree age, density, and cooling effect, with mature trees at higher densities providing significant air temperature reduction - up to 6°C cooler during the day and 4°C at night beneath the canopy. Trees younger than 20 years will likely provide less cooling due to reduced leaf area and shading. These findings will prove valuable for urban planners implementing tree planting as a thermal buffer against heatwaves. The study offers a wide range of numerical tree parameters demonstrating the cooling effects of urban forest canopies on local microclimate at high spatial-temporal resolution.