Modelling the impacts of soil sealing and climate change on urban tree growth and cooling in public squares of Munich

Trees are crucial for mitigating the urban heat island effect, but their growth and cooling capacity are increasingly challenged by climate change and extensive soil sealing. This study analyzed how surface sealing and future climate conditions jointly affect tree growth and microclimatic cooling across 25 public squares in Munich, Germany. Using the process-based CityTree model, we simulated biomass increment per unit basal area and transpiration-driven cooling under current climate (1991–2020) and future (2081–2090) climate conditions, following the Representative Concentration Pathway (RCP) 8.5 from the IPCC Fifth Assessment Report (AR5). These simulations were complemented by empirical air temperature measurements (iButton sensors) collected during one summer season to characterize current shade-cooling patterns. Model results indicated that reducing soil sealing by 20% under current conditions enhanced biomass increment by 21.5% and canopy cover by 25%, accompanied by a 13.2% increase in cooling efficiency through transpiration. Under the RCP 8.5 scenario, predicted biomass increment and canopy cover declined by 16.5% and 15%, respectively, while the cooling improvement due to soil unsealing weakened to about 4%, reflecting constraints from higher temperatures and reduced water availability. Empirical microclimatic measurements revealed substantial variation in shade-cooling effects: at Alpenplatz (56% canopy cover), air temperatures dropped by up to 2.7 °C during peak hours, while heavily paved squares such as Bordeauxplatz and Marstallplatz showeed smaller reductions of 1.4 °C and 1.8 °C, respectively. These findings highlight the pivotal role of soil permeability and spatial design in maintaining tree vitality and microclimatic regulation in densely built urban environments. Analyzed the combined impacts of soil sealing and RCP 8.5 climate change on urban tree performance in Munich, Germany. Under the future RCP 8.5 scenario, modelled growth and transpirational cooling are projected to decline by 16.5% and 5.6%, respectively. The effectiveness of unsealing for cooling is projected to weaken under future climate (~ 4%) as drought-induced stomatal closure limits latent heat flux. Empirical measurements confirm that canopy density is the primary driver of pedestrian-level cooling, with air temperature reductions up to 2.7 °C.