Urban trees grow in a very heterogeneous environment. In addition to the demanding growing conditions due to small planting pits with limited rooting space and sparce water availability, heat, pollution and much more, above-ground space requirements because of safety reasons and aesthetic demands affect urban tree growth. Management practices such as pruning are a common measure for many urban tree species to adjust the crown for aesthetic requirements and size constraints such as buildings, other trees or above ground cables. On the other hand, these pruning measures alter tree growth and thus ecosystem services such as cooling, CO2 sequestration and runoff reduction. To maintain or improve growth and the provision of ecosystem services despite the challenging conditions in urban environments, trees can be irrigated, particularly during periods of drought. Our research analyzes the influence of management (pruning and irrigation) on tree growth and the provision of ecosystem services such as cooling on the common urban tree species Platanus x acerifolia in cities. Plane trees are often selected for aesthetic pruning due to their high pruning tolerance, robustness and fast growth. For this study, the tree structures more than 350 pruned and unpruned trees in Munich and in a tree nursery were measured and their growth conditions compared. The modeling tool CityTree was used to calculate the biomass accumulation and provided ecosystem services carbon storage and cooling by shading and transpiration of pruned and unpruned trees, with and without irrigation. The results show clear differences in growth, tree parameters such as leaf area, biomass, photosynthesis and provision of ecosystem services between pruned and unpruned trees, with irrigation helping to survive drought periods. The results can be useful for urban planners regarding management practices in urban tree planning to create more efficient management plans and increase the vitality of urban trees.

How to cite: Rötzer, T., Moser-Reischl, A., Shu, Q., Franceschi, E., and Ludwig, F.: Influence of tree management (pruning, irrigation) on growth and ecosystem service provision of Platanus x acerifolia, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-366, https://doi.org/10.5194/icuc12-366, 2025.

Urban trees are pivotal in mitigating urban heat, addressing climate change challenges, and enhancing urban resilience and sustainability. Their cooling effectiveness is governed by a complex interplay of background climate, urban morphology, and tree traits [1]. Our study synthesizes data from 182 studies across 17 global climate zones to quantify the cooling potential of trees in diverse urban settings. Results reveal a non-linear amplification of cooling benefits by up to 12°C with increasing background temperatures, particularly in open urban areas (LCZ 4-6) and hot, arid climates. The use of mixed-species plantings, integrating deciduous and evergreen trees, demonstrates enhanced cooling benefits, particularly in open urban forms. However, challenges such as stomatal closure during extreme heat events and the entrapment of longwave radiation in compact urban environments (LCZ 1-3) highlight the necessity for context-specific planning. The findings emphasize the critical importance of strategically selecting and situating the “right tree” in the “right place,” guided by both current and future climatic conditions. Evidence-based guidelines emphasize the prioritization of climate-appropriate tree species, optimization of ground space for root and canopy growth, and integration of tree planting into urban planning processes. By bridging urban climate science and urban design, we offer actionable insights to support cities in adapting to a warming climate, ultimately enhancing livability and sustainability. 

[1] Li, H., Zhao, Y., Wang, C. et al. Cooling efficacy of trees across cities is determined by background climate, urban morphology, and tree traits. Commun Earth Environ 5, 754 (2024).

How to cite: Li, H., Zhao, Y., Wang, C., Ürge-Vorsatz, D., Carmeliet, J., and Bardhan, R.: Insights into tree-centric urban cooling: A global meta-analysis of 182 studies across 17 climate zones, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-191, https://doi.org/10.5194/icuc12-191, 2025.

Excess heat in cities, also known as the urban heat island (UHI) effect, has impacts on human comfort, productivity, and mortality. To mitigate this urban heat risk, one of the most prominent measures is increasing the vegetation fraction in urban environments. However, cooling effect intensity of urban vegetation compared to surrounding built-up environments, is highly variable as it depends on internal characteristics of the city, on the design of urban greening and on large-scale weather conditions.

We quantify the nocturnal cooling effect intensity of urban parks in the Paris region and its day-to-day variability (1 to 5°C cooling) based on in-situ temperature measurements during three consecutive summer periods (2022-2024). Using a wind profiling Doppler Lidar to measure turbulent vertical mixing conditions above the Paris city centre, we relate the park cooling intensity to the turbulent mixing conditions in the nocturnal urban boundary layer. We identify three mixing regimes that explain the day-to-day variability in park cooling intensity for several green spaces across the Paris Region, as the relative importance of radiative and turbulent cooling processes in the urban canopy layer differ between regimes. This regime analysis allows us to characterise the park cooling intensity of green spaces of various sizes and configurations (about 1 to 20 ha) and we further assess how this cooling benefits the surrounding built-up areas. Finally, we show that the mixing regimes are valuable when linking the air temperature UHI with spatial contrasts in satellite-derived surface temperatures.

Our results highlight that the stability regimes provide a powerful framework for the assessment of nocturnal urban heat risk and the quantification of urban vegetation cooling intensity as they enable more meaningful comparisons between different locations, conditions, and periods of investigation.

How to cite: Haeffelin, M., Ribaud, J.-F., Kotthaus, S., Cespedes, J., VanHove, M., Dupont, J.-C., Lemonsu, A., Masson, V., and Nagel, T.: Urban Heat Mitigation: The Influence of Turbulent Mixing in the Nocturnal Boundary Layer on Vegetation Cooling Effects, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-856, https://doi.org/10.5194/icuc12-856, 2025.

Existing observational studies on the cooling effects of different urban green space types yield conflicting results.  Few studies have compared the differential thermal environmental impacts of urban green space types while controlling the environmental contexts.  To fill the research gap, we adopted a mesoscale model coupled with an urban canopy model to quantify and compare such differential impacts in a subtropical city located in central China.  Mixed trees, the predominant green space type in the city, showed the best model performance.  In most places, closed shrubs yielded the strongest daytime cooling of 0.4℃ while the weakest humidification of 0.15g/kg, thus reducing the regional mean heat index (HI) by 0.38℃.  Mixed trees had a limited effect on 2-m air temperature but greatly raised near-surface moisture content by 0.8g/kg, thus increasing the regional mean HI by 0.2℃.  However, in locales with the green space fraction larger than 0.6, mixed trees produced the strongest cooling of 0.6 – 1.3℃.  This was because evapotranspiration instead of albedo drove the cooling process.  At night, all the green space types showed stronger cooling but weaker humidifying effects.  Of all, mixed trees led to the largest reduction in temperature (by 0.6℃ on average) and the HI (by 0.56℃), while grass showed the strongest humidification of 0.35g/kg.  The nighttime cooling was attributed to the reduction in sensible and ground heat flux by green space compared with impervious surfaces.  We suggest prioritizing closed shrubs in small green patches and paying attention to the humidification of grass at night.

How to cite: Cao, Q. and Deng, X.: Differential thermal environmental impacts of green space types in a subtropical city: Evidence from mesoscale modelling, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-22, https://doi.org/10.5194/icuc12-22, 2025.

Rising air temperatures and prolonged hot spells are increasing the role of urban vegetation. Urban parks and all nature-based solutions introduced in cities play a huge role in climate change adaptation. In Warsaw (Poland), urban greenery (parks, river valleys, and allotment gardens) accounts for 15.5% of the area, and forests account for another 15%. However, the city planned to reduce this area by 5% by 2050. The average intensity of the urban heat island in urban greenery is 0.6°C, compared to 2.6°C within intensive inner city development or 2.8°C near major transport arteries. This confirms the great role of greenery in shaping urban climate and bioclimate.

The results of the CLIMPARK project examining the climate of 6 parks in Warsaw with areas ranging from 3.5 ha to 78 ha indicate that during summer, the air temperature on the permanent meteorological stations located in open spaces in the parks is, on average, 1.0°C-1.5°C lower compared to the built-up area. However, the 10-minute differences between these locations reach 6.5°C, while the differences between shaded parts of the park and the built-up area exceed 8°C. During the cold half of the year, average differences are smaller and amount to 0.6-0.8°C.

The thermal differences within the park can also be significant depending on its size, the structure of the vegetation, and the site itself. Average differences between shaded and sunny areas recorded in the park in the summer exceed 3°C, and the differences in 10-minute values reach 5°C. The project attempts to develop a model of the intensity of the air cooling effect depending on the park's features. The impact of parks on reducing the exposure to heat stress of people living in their vicinity will also be estimated.   

How to cite: Kuchcik, M., Czarnecka, K., Baranowski, J., Jarocińska, A., Kowalska, A., Lindner-Cendrowska, K., and Słowińska, S.: Climate Diversity of Urban Parks: Exploring the Influence of Size, Composition, and Greenery Features, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-272, https://doi.org/10.5194/icuc12-272, 2025.

Urban forests have emerged as a key strategy for promoting adaptive capacities of cities to climate change by mitigating urban heat island (UHI) and thus heat stress for humans. An empirical study in Würzburg, Germany (2018–2020) revealed a significant increase in extreme heat conditions, with nine days exceeding a Wet Bulb Globe Temperature (WBGT) threshold of 35°C in the treeless city center, compared to none in a treed suburban site just five kilometers away.

Further research in Munich, Germany, comparing two ecologically contrasting tree species, Tilia cordata and Robinia pseudoacacia, under varying meteorological and soil conditions highlighted that shading is the dominant cooling mechanism, particularly under high atmospheric aridity. In temperate climates with adequate soil moisture, lighter shaded canopies may enhance grass evapotranspiration, suggesting a preference for dense canopies over built environments and lighter canopies over grass surfaces.

To explore cooling mechanisms across climates, sensible and latent heat fluxes under tree canopies within various settings (park, street, square) were analyzed in Munich (temperate) and Beer Sheva, Israel (hot arid). Despite irrigation, trees in Beer Sheva exhibited higher hydraulic resistance, limiting transpirational cooling (regression slopes of 0.25–0.44 in Beer Sheva vs. 0.10–0.18 in Munich). Analysing the proportion of latent heat to total available energy, we found transpiration cooling was about 40% less significant at noon hours in summer in Beer Sheva than in Munich. These results suggest that with anticipated higher atmospheric aridity, shading will become even more important, thereby, denser tree canopies would be of higher importance.

Additionally, LiDAR scanning revealed that multilayered vegetation enhances cooling benefits more than twofold compared to single-layered vegetation. Thus, increasing vegetation complexity both horizontally and vertically can optimize thermal benefits through shading and transpiration across diverse climates, while also supporting biodiversity and fostering nature connectedness.

How to cite: Rahman, M. A., Moser-Reischl, A., Pattnaik, N., Franceschi, E., Wang, X., Rötzer, T., and Pauleit, S.: Optimizing urban forests for climate resilience: shading, transpiration, and multilayered vegetation in mitigating heat stress across climates, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-329, https://doi.org/10.5194/icuc12-329, 2025.

In order to mitigate the impacts of climate change in urban areas, there is a growing emphasis on the promotion of nature-based solutions (NBS) with expected benefits for biodiversity, rainwater management, evaporative cooling, and carbon sequestration. Among the various possible NBS, green facades have the advantage of being deployable in already built area. The environmental evaluation of greening policies through the implementation of green facades requires integrated physical-based numerical model to simulate radiative, energy, and carbon exchange processes at building scale but within a modelling framework that can also address interactions at the neighbourhood and city level.

Here, the urban canopy model Town Energy Balance (TEB, Masson, 2000) is revised with the implementation of a new green façade module informed with micrometeorological and ecophysiological observations collected on an experimental green façade site located in Berlin, Germany (Hölscher et al, 2016). The first step is the improvement of short- and long-wave radiative exchanges in TEB by considering an additional vegetation layer fixed to the wall. We now take into account the processes of interception of radiation by the vegetated layer, of transmission through it (depending of leaf density), and of absorption, as well as the inter-reflections within the canyon including new contributions from green façade.

First results show that the model is able to represent the effect of the vegetation foliage and its evolution on the radiative balance. This constitutes the first step in achieving the fully integrated modelling of the impact of green façades on the urban climate in TEB.

Reference :

Hölscher, M.-T., Nehls, T., Jänicke, B. and Wessolek, G., 2016. Quantifying cooling effects of facade greening: Shading, transpiration and insulation. Energy and Buildings, 114: 283–290.

Masson, V., 2000. A physically-based scheme for the urban energy budget in atmospheric models. Boundary-Layer Meteorology 94: 357–397.

How to cite: Mirebeau, A., de Munck, C., Lemonsu, A., Weber, S., Delire, C., and Garrouste, O.: Modelling green façades radiative exchanges within the TEB (town energy balance) urban canopy model, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-417, https://doi.org/10.5194/icuc12-417, 2025.

How to cite: Yan, C. and Miao, S.-G.: Evaluating the thermal influences of a finite-size forest under varying microclimatic conditions, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-518, https://doi.org/10.5194/icuc12-518, 2025.

Green infrastructure serves as essential sources of natural cooling and social interaction, critical for city dwellers in mitigating heat risk under global warming. Their distribution is influenced by natural environments and urbanization stages, which often correlate with socioeconomic features, leading to inequalities in heat adaptation. This study provides a dynamic perspective by analyzing temporal changes in temperature anomalies, green space patterns, and social vulnerability to heat. Using six urban agglomerations at different urbanization stages in Northern Taiwan as case studies, this study evaluated how urban development has shaped the relationship between green spaces and heat risk between 2009-2012 and 2019-2022 periods, focusing on the changing patterns of cooling and social provisions from green spaces.

Results reveal distinct geographical variations in warming patterns, social vulnerability, and heat risk. While less fragmented green spaces contributed to lower temperatures, increases in green spaces did not necessarily reduce warming. In major cities, populations highly vulnerable to heat stress had better access to the cooling benefits of green spaces. In most cities, green spaces available for social interaction were more available in areas with higher vulnerable populations during 2009-2012, while this relationship has weakened in recent years. Spatial analysis revealed clustering patterns between changes in green spaces and heat risk. Within Taipei Basin, green spaces tended to increase in the city center with either rising or declining heat risk, while decreasing in peri-urban areas with rising risk over the study period. This temporal assessment of heat risk inequality provides insights for decision makers, suggesting that nature-based solutions through strategic green space planning must not neglect constant negative impacts from further urbanization, different warming intensity, and social vulnerability changes over time, instead of viewing nature-based solutions as a panacea.

How to cite: Shih, W. and Ou Yang, T.-L.: Temporal Changes in Green Infrastructure and Heat Risk Inequality across cities of Northern Taiwan, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-804, https://doi.org/10.5194/icuc12-804, 2025.

Global warming and heat waves are expected to amplify the vulnerability of major cities during the 21^st Century. This risk may exacerbate the effects of Urban Heat Island (UHI). In response, adaptation measures are being studied for urban areas.

As part of its adaptation strategy, the City of Paris is working on various projects to create urban cool islands in order to limit the pedestrian heat stress during heatwave periods. One of these is to create several urban forests, including the Bois de Charonne Forest along the Petite Ceinture near Porte de Vincennes in the East of Paris. The urban forest opens a new portion of the petite ceinture to the public with a high proportion of vegetation following the planting of many trees. The microclimatic effects of the creation of the urban forest is studied to evaluate its impact on pedestrian heat stress and UHI intensity.

Fixed and mobile microclimatic measurement campaigns were conducted before (summer 2023) and after (summer 2024) site transformation and vegetation planting. Three fixed weather stations are used. Two are located in different zones of the urban forest, and a third serves as a control station outside the site. Mobile measurements were carried out at specific locations to increase the study’s spatial coverage.

Observations indicate a small improvement of microclimatic conditions depending on the area studied.

How to cite: Abboud, C., Chaumont, M., Grados, M., Joffrin, S., Hendel, M., and Royon, L.: Impact of an urban forest on pedestrian heat stress and UHI mitigation in Paris, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-843, https://doi.org/10.5194/icuc12-843, 2025.

How to cite: Budhiraja, B., Wanner, A., McKinley, J., Pröbstl-Haider, U., and Jungnickel, M.:  Challenges created by the Austro-Hungarian Empire: Addressing Urban Heat Inequality through Nature-based Solutions in Vienna and Budapest, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1058, https://doi.org/10.5194/icuc12-1058, 2025.