In Berlin, Germany, new laws have been passed in the past 5 years seeking to transform the city’s mobility infrastructure to be climate neutral and environmentally friendly. Given Berlin’s size, history, and diverse governance structures, these new mobility measures (e.g. new bike lanes, temporary street closures) are typically implemented piecemeal in heterogeneous districts that makes measuring their individual environmental impacts challenging. Using the transdisciplinary research approach of the Research Institute for Sustainability of the Helmholtz Centre Potsdam (RIFS), the planning and execution of several measurement campaigns, and the subsequent uptake of results into policymaking, was conducted with local stakeholders in the Berlin Senate Department for the Environment, Urban Mobility, Consumer Protection and Climate Action (SenUMVK). To assess individual measures’ impacts on local air quality, a metric important to policymakers’ assessments of their success, before and after measurements of nitrogen oxides (NO_x) and particulate matter (PM) were conducted. This talk will focus on the transdisciplinary approach to research and how such an approach can address air pollution and climate change synergies, but also how such an approach facilitates uptake of research results by decision-makers.

How to cite: von Schneidemesser, E., Schmitz, S., Caseiro, A., and Kerschbaumer, A.: A transdisciplinary approach to improving urban air pollution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15678, https://doi.org/10.5194/egusphere-egu24-15678, 2024.

In the earth’s atmosphere, volatile organic compounds (VOCs) are emitted from natural (biogenic) and anthropogenic sources. VOCs are important components of photochemical processes with strong significance to atmospheric chemistry and climate change through the formation of ozone and organic aerosols. Despite their large biogenic emissions and strong photochemical cycling under the tropical conditions, the speciated measurements of biogenic-VOCs (BVOCs) over the South Asia region are extremely rare. Recently, a project “Network of Volatile Organic Compounds (VOCs) Measurements in India: Biosphere-Atmosphere Exchange” has been implemented for the measurements of BVOCs over different environments of India and surrounding oceanic regions. We have conducted ambient air measurements of C6-C12 compounds at an urban site of Ahmedabad in western part of India during January-May 2020. The well time resolved continuous measurements provided excellent dataset to characterize the diurnal, day-to-day, and seasonal variations of VOCs originated from both biogenic and anthropogenic sources. The mains scientific focus of this study is to characterize the ambient air variations of α- and β-pinene, which are the main representatives of the monoterpene group. Unlike the large reductions in concentrations of anthropogenic VOCs during summer also coinciding with COVID-19 lockdown, the mixing ratios of α- and β-pinene showed a strong increasing trend from winter to summer. The monoterpenes showed clear diurnal patterns with higher night-time and daytime concentrations during winter and summer season, respectively. The monthly mean mixing ratios of α-pinene and β-pinene varied n the ranges of 10-22 and 3-16 pptv, respectively. Despite minimum anthropogenic influences and intense photo-oxidation loss in summer of 2020, the huge enhancements of monoterpenes in ambient air indicate the strong biogenic emissions from local vegetation. Our analysis indicate the combined effect of the northwest wind flow and higher air temperatures leading to high emissions of BVOCs from local vegetation.

How to cite: Sahu, L., Malik, T., Gupta, M., and Tripathi, N.: Changes in ambient concentrations of monoterpenes during the winter-summer transition period in an urban site of India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1147, https://doi.org/10.5194/egusphere-egu24-1147, 2024.

The significant transformations from rural to urban living encompasses substantial challenges related to climate action and sustainable development. Gaseous pollutants that were traditionally associated with rural livelihood are now also a challenge to urban ecosystems with CO being a prime example. Despite an overall decline in CO across the globe, the rate of decrease has actually slowed down in several regions of the world raising concerns of a global reversal. The trends in CO are found to be heterogeneous over urban regions of the world and concentrations do not always tally with emission inventories. Further, it is not only the trends that are changing over decades but also the global hotshots of several air pollutants, SO2 being a key example with the high values in Eastern China during the 2000s to enhanced values in Eastern India during the 2010s. Interestingly, when it comes to SO2, driven by the burning of coal, the hotspots in India are not in the Indo-Gangetic Plains (IGP) unlike CO or NH3, which are though driven by different sources e.g. combustion technologies and agricultural activities, respectively. Further, pollutants that were associated with indoor air studies with ramifications to human health are now increasing significantly at several locations in outdoor air, HCHO being a prime example. While the concentration of CO in India occurs in the IGP, unexpectedly enhanced formaldehyde levels were seen in certain pockets of India, away from the IGP, with trends that are higher than reported HCHO values across several parts of the globe. Apart from primary sources, HCHO is also an oxidation product of atmospheric volatile organic compounds (VOCs) and the high trend in HCHO observed during the summer months, generates interest on possible implications of atmospheric chemistry on ozone formation regimes in urban ecosystems. The changing temporal and spatial patterns necessitate mitigation strategies that do not completely depend on emission control and reduction but use alternate strategies like nature based solutions (NBS), particularly for urban ecosystems that harbor a larger population.

How to cite: Mallik, C.: The see-saw relationship of air pollution with climate: novel challenges to urban ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-745, https://doi.org/10.5194/egusphere-egu24-745, 2024.

The Atmospheric Boundary Layer (ABL) represents the critical interface between the Earth's surface and the free atmosphere, playing a pivotal role in shaping weather patterns, air quality, and the dispersion of pollutants. This study comprehensively investigates the ABL dynamics over the Western-Indian region during 2019-2023. Continuous observation of ABL is made over the Western-Indian region's three locations: Ahmedabad, Mount Abu, and Udaipur. Ahmedabad (23.02° N, 72.57° E) is a highly polluted urban location in the Indian state of Gujarat with a hot, semi-arid climate, while Mount Abu (24.59° N, 72.71° E) is a high-altitude location in the Aravalli range of mountains in Rajasthan. On the other hand, Udaipur (24.58° N, 73.71° E) is close to the desert region in Rajasthan, surrounded by lakes and having a hot semi-arid climate. The ABL is continuously monitored over these stations using a ground-based Ceilometer lidar. By analyzing observational data collected from diverse geographical locations, we seek to identify regional variations in ABL characteristics and their consequences on local weather systems. Results indicated a large winter-summer difference in ABL over Ahmedabad, with summer Boundary Layer Height (BLH) exceeding winter BLH by 1–1.5 km. These differences were less over the Mount Abu and Udaipur region. The ABL usually collapses over all three study regions during monsoon and is thicker during the pre and post-monsoon. Ground-based observation of ABL using lidar has been compared with the radiosonde, satellite, and reanalysis datasets. The ERA5 reanalysis underestimated the BLH, especially the nocturnal boundary layer height. Due to the proximity to the Thar desert, the study sites witness dust storms. The study also investigated the impact of dust storms on the ABL. Through a combination of advanced measurement techniques, such as lidar and satellite observation, we aim to provide a nuanced understanding of the spatiotemporal variability of key ABL parameters. In conclusion, this study aims to contribute to understanding how the ABL responds to changing climate conditions and its role in modulating the Earth's energy balance. By enhancing our understanding of ABL dynamics, we can improve the accuracy of weather predictions, refine climate models, and develop strategies for mitigating the impact of air quality issues on human health and the environment.

How to cite: Kamat, D., Sharma, S., Saha, S., Kumar, P., and Kumar, N.: Exploring the dynamics of the Atmospheric Boundary Layer over the Western-Indian region: Insights and Implications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-856, https://doi.org/10.5194/egusphere-egu24-856, 2024.

Sundarbans is a biodiversity hotspot sprawling across eastern India and Bangladesh, often subject to various biospheric research. Despite being one of the keys to coastal resilience building and climate change mitigation,  it remains one of the most vulnerable areas in terms of environmental degradation and economic instability. This multi-dimensional study aims to look into the temporal evolution of air pollutants like nitrogen oxides (NOx), particulate matter (PM), Sulfur dioxide (SO2), carbon monoxide (CO) and carbon dioxide (CO2) along with the urbanization of the highly sensitive biodiversity hotspots of Sundarban Deltaic Region by using long-term satellite and reanalysis datasets. The time series analysis of the air pollutants, including PM, NOx, CO, and CO2 showed an increasing trend of the pollutant concentrations, mostly owing to anthropogenic sources and climate change. The enhancement of air pollutants along with climate parameters like temperature indices within densely vegetated regions such as the Sundarbans, a biodiversity hotspot, raises considerable concern especially when the region’s socio-economic statistics have also deteriorated over the years.

This study also aims to assess the effectiveness of NBS in carbon sequestration through mangrove plantations implemented by diverse stakeholders over time. Further, the socio-economic dynamics of communities depending on mangrove resources were studied by utilizing various district-level surveys, plantation statistics, field surveys and stakeholder consultations. It was found that the communities have been most dependent on the mangrove species for firewood even after the advent of LPG which does undermine the Government’s efforts for clean fuels in homes. Though the households continue to graze cattle and use firewood, the awareness amongst the vulnerable populations regarding the importance of mangroves has improved. The planting of mangrove trees has not only contributed to ecological benefits but also brings in economical benefits for the communities involved. The initiative carried out in areas identified as vulnerable under the Panchayat's Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA) 100-day work scheme, aims to provide employment opportunities to rural households by guaranteeing at least 100 days of wage employment per year, and in the context of mangrove plantation, it aligns both environmental conservation, economic development goals and women participation. Women's participation is actively observed in the plantation and maintenance of mangroves, which gives them economic benefits at the same time aligning with the goals of habitat preservation and climate mitigation. This symbiotic relationship proves to be the key to several potential environmental initiatives that positively impact the livelihoods of local populations.

How to cite: Ganguly, V. and Mallik, C.: Multi dimensional Assessment of Air Pollution Evolution in the Sundarban Deltaic Region in context of Climate Change and Socio-Economic Dynamics., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1195, https://doi.org/10.5194/egusphere-egu24-1195, 2024.

Cities and towns have become the primary human living space as they offer many opportunities for people, such as employment, educational opportunities, medical assistance, cultural and recreational activities.  According to the United Nations studies, the level of urbanization is expected to increase all over the world. Planning a sustainable rapid urbanisation becomes therefore crucial, and it requires scientific based evidence also regarding the effects of vegetation on urban atmosphere considering the urban built structure and all emission sources. This information is also important for urban regeneration making use of nature-based solutions (NBS) and aiming at improving air quality and reducing the impact of climate changes.

It is largely recognised that vegetation contributes to reduce the air temperature and to remove air pollutants in cities, but the impact of its emissions on air quality, together with its effects on the dispersion capacity of the atmosphere, are less known. Biogenic volatile organic compounds (BVOC) that vary with specie and with meteorological conditions, are continuously emitted by vegetation in the atmosphere contributing to the generation, destruction, and transformation of atmospheric pollutants such as gases (O₃ and its precursors) and aerosol particles (PM10).

Here, a comprehensive assessment of vegetation effects on urban atmosphere will be shown for two Italian cities, Bologna and Milan, using the approach proposed in the European project Life VEG-GAP (https://www.lifeveggap.eu/). Specifically, the role of vegetation on urban meteorology is investigated, followed by an evaluation of its impact on air quality. Thus, the direct effects of vegetation on pollution through removal and emission processes are distinctly evaluated from its “indirect” effect acting through meteorology.

The assessments are based on numerical simulations carried out with a state-of-the-art air quality modelling system that uses the chemical transport model FARM and the meteorological model WRF. The BVOC emissions were produced with the species-specific model PSEM and the urban trees inventories provided by the Municipalities.

The outcomes show: 1) the contribution of vegetation ecosystems both as a source and a sink of air pollution in urban areas; 2) the urban vegetation ecosystems' effects on air temperature (urban heating and cooling patterns) and 3) its impact on air quality for the most relevant pollutants (O₃, NO₂, PM10). They also show the relationship between the presence of vegetation and temperature, pollutants’ concentrations, and depositions, according to land-use classes and vegetation fraction.

The intercomparison of vegetation effects on urban atmosphere for Bologna and Milan shows that their magnitude, pattern, and space/time variability are city dependent for both meteorological and chemical quantities. In addition, the continuous changes of large-scale meteorological conditions lead to a high variability in the ecosystem services of vegetation that can be realistically assessed only using a VEG-GAP-like approach and cannot be resumed in a simple quantification at city-scale.

How to cite: Mircea, M., Briganti, G., Russo, F., Finardi, S., Silibello, C., D'Isidoro, M., Villani, M. G., Cappelletti, A., Adani, M., D'Elia, I., Piersanti, A., Vitali, L., Bolignano, A., Pepe, N., Prandi, R., and Carlino, G.: Vegetation role in urban atmospheric dynamics and chemistry: comprehensive assessment in two Italian cities , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18978, https://doi.org/10.5194/egusphere-egu24-18978, 2024.

The literature extensively discusses the potential of trees to enhance urban air quality by removing particulate matter (PM), highlighting it as one of the numerous advantages of trees in urban settings. To optimize the layout of green spaces in urban and peri-urban areas with restricted open space, it is crucial to choose appropriate tree species capable of maximizing PM removal. Regarding the PM absorption capacity in leaves, recent findings have primarily focused on establishing connections with complex leaf shapes, large surface areas, trichome shapes or other associations. Depending on which tree species were tested, factors that had a major influence on the adsorption capacity of PM used to show differently. So, we evaluated the relationship between leaf anatomical traits (microstructural properties) and PM adsorption capacity in 150 species in Korea. As a result of our study, a weak relationship was observed between microstructures (trichome density located in the main vein, lateral vein, lamina, stomatal density, roughness, leaf length, leaf area) and the PM adsorption capacity in 150 tree species. We suggest that the microstructures associated with PM adsorption capacity are likely a combination of complex factors rather than a single major factor. To gain clearer insights, we plan to conduct analyses on the same genus with similar microstructure characteristics but varying morphological differences, such as density and length. Additionally, we intend to analyze two to three composite characteristics of microstructure. 

How to cite: Je, S. M., Jeong, S. G., Chang, H., and Son, J.-A.: Analyzing the relationship between the leaf anatomical traits and PM adsorption capacity of 150 major landscape tree species in Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14199, https://doi.org/10.5194/egusphere-egu24-14199, 2024.

Air pollution has become a prime concern globally due to the escalation of anthropogenic activities and adverse meteorological conditions in recent years. The significant consequences of air pollution, manifesting in adverse ecosystem health effects and economic losses, highlight the urgency of assessing its impact on a regional to global scale. However, there is a lack of systematic investigations, particularly in the context of information deficiency on air pollution in Bangladesh. Therefore, this study aims to investigate the seasonal variations in air quality over Dhaka and Kolkata, with a specific focus on the summer monsoon (May-July). While winter pollution in these cities has been extensively explored in several studies, less attention has been given to understanding the dynamics of monsoon season. This study incorporates Copernicus Atmosphere Monitoring Service (CAMS) reanalysis data to evaluate the influences of both regional and global factors on air quality. Specific emphasis has given on determining the correlation between air pollutants (PM_2.5, carbon monoxide, black carbon, sulfur dioxide, ozone, nitrogen dioxide) and meteorological parameters (temperature, humidity, wind components, atmospheric pressure, boundary layer height and precipitation). This understanding is crucial as it forms a strong foundation for developing effective control and prevention strategies of air pollution for this region. In addition, by correlating metrological conditions between Dhaka and Kolkata, the study aims to evaluate the transboundary effects on pollutant dispersion. The potential impact of Sahara fires on air quality of these two cities is investigated using concentration-weighted trajectory analysis (CWT), extending the geographical domain to include the entire South Asian region. The findings not only contribute to the scientific understanding of local air quality but also have broader implications for regional and global atmospheric interactions. The study's insights provide a basis for informed policymaking and facilitate more effective nature based mitigation and control management strategies during the summer monsoon season in these densely populated urban areas.

How to cite: Faruk, T. and Khan, F.: Monsoonal Transboundary Impact on Air Quality over Dhaka and Kolkata Region , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-710, https://doi.org/10.5194/egusphere-egu24-710, 2024.

Green spaces in cities have been demonstrated to offer multiple benefits to their inhabitants, including cleaner air, shade in sunny periods, and a place that contributes to mental well-being. In addition, trees in cities are home to several species of animals and work as a nature-based solution that can sequester CO2 and regulate water storage in urban ecosystems. The 3-30-300 rule space rule has been suggested as a strategy for city planners regarding urban forestry. This rule states that every resident’s home or workplace should be close to at least three trees, every neighbourhood should have a 30% canopy cover, and every citizen should have access to a public green space within a 300 m radius. Following this rule guarantees that all citizens obtain all the benefits of urban vegetation; however, this is not the case for all areas, particularly those impoverished ones where access to green spaces is limited, further contributing to social inequality. This study delves into the implementation of this rule across major UK urban areas, employing a blend of remotely sensed imagery, census data, ordnance surveys and machine learning methods. Our findings offer vital insights for city planners, emphasizing the need for a strategic approach to urban green space distribution that fosters social equity and environmental sustainability.

How to cite: Zuñiga-Gonzalez, A., Madhavapeddy, A., and Bardhan, R.: Green Urban Equity: Analyzing the 3-30-300 Rule in UK Cities and Its Socioeconomic Implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20833, https://doi.org/10.5194/egusphere-egu24-20833, 2024.

How to cite: Daelman, T., Verbeeck, H., Vancoillie, F., and Demuzere, M.: Utilising Terrestrial Laser Scanning (TLS) for urban tree structure characterization and its impact on modelled human thermal comfort, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5790, https://doi.org/10.5194/egusphere-egu24-5790, 2024.

Increasing tree canopies is one of the effective measures to reduce heat at different spatial scales in cities. From a human-biometeorological perspective, tree canopies cool the trunk space below by reducing solar radiation, thus providing shade and lowering the net radiation overall. They also reduce the air temperature above them through transpiration, but this process also increases the water vapor pressure, which slightly counteracts a lowering of human heat stress. However, these two effects mainly affect the layer above the tree canopies. Therefore, they are less likely to promote the lowering of outdoor human heat stress at the pedestrian level below the tree canopies.

As a valuable benefit for the enhancing of human thermal comfort in urban areas, the cooling potential of tree canopies depends on their dimension, shape and leaf density. Even if trees have comparable physical states, they may influence the micrometeorological variables that control local human thermal comfort differently in various climate zones. In this context, the study shows the human-biometeorologically significant cooling potential of street trees at two exemplary selected urban sites in different climate zones. According to the Köppen and Geiger climate classification, the Jeju site (N 33˚ 49'00'', E 126˚ 50'00''), Republic of Korea, is in the Cfa climate zone, whereas the Stuttgart site (N 48˚ 46'38'', E 9˚ 10'30''), Germany, is in the Cfb climate zone.

Based on the validated version of the ENVI-met v5.0.2 software, systematic simulations were conducted on typical summer days to show the effect of various tree canopy characteristics, which refer to two tree dimensions, two values of the leaf area index (LAI), and three shapes of tree crowns (ellipsoid, triangle, and inversed triangle), on the level of outdoor human thermal comfort at both sites.

In the simulation results for sunny conditions, it is noticeable that tree canopies in the shape of ellipsoids exhibit the highest reduction in mean radiant temperature (T_mrt), which is considered a key factor in human thermal comfort. In Jeju it varies between 6 and 25 K and in Stuttgart between 11 and 27 K. The remarkable reduction of T_mrt leads to a maximum cooling potential of the physiological equivalent temperature (PET), as quantitative measure for human thermal comfort, of 12 K in Jeju and 14 K in Stuttgart. Assuming that the PET classification applies to both climate zones, the result is that the level of PET classification at both locations in different climate zones decreases from “very hot” to “warm”. 

This research forms the basis for complementary studies on the human-biometeorologically significant cooling effect of tree canopies with various characteristics that extend to other different climate zones.

How to cite: Lee, H., Park, S., Mayer, H., and Kim, J.: Tree canopy characteristics influence human heat stress reduction: comparative case study for two sites in different climates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6879, https://doi.org/10.5194/egusphere-egu24-6879, 2024.

Global warming and urbanization growth are accelerating and fuelling typical urban stressors including microclimate alterations with an intensification of urban heat islands (UHI). UHI areas are characterized by warmer temperatures with respect to the surrounding rural areas, affecting human health and mortality. Trees and urban green areas (UGAs) have been shown to be crucial in reducing the UHI because of the canopy transpiration-induced cooling: by turning liquid water to vapor absorbing heat energy from the surrounding environment, solar radiation is converted into latent heat flux, which lowers air temperatures surround. In this study conducted over 10 European cities we investigated if and how much UGAs impact latent heat fluxes and the related ambient air cooling, and how UGAs could be used to develop more habitable and sustainable urban environments. Specifically, the objectives of the study are to: 1) assess the impact of the green areas in cooling down the air temperature in summer months using in situ eddy covariance (EC) measurements and 2) assess the role of the environmental factors driving the latent heat fluxes and, consequently, the related cooling of urban microclimate. Results confirm that green areas within urban environments are key elements for enhancing the summer air cooling and thus the well-being of local inhabitants.

How to cite: Guidolotti, G., Shaukat, S., Ciolfi, M., Mattioni, M., Nicolini, G., Sabbatini, S., Calfapietra, C., and Papale, D. and the Sites PI: Vegetation to cool cities: a synthesis based on eddy covariance measurements in European cities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7823, https://doi.org/10.5194/egusphere-egu24-7823, 2024.

Increasing the urban tree cover percent (TCP) is widely recognized as an efficient way to mitigate urban heat. However, in the context of global warming, the response of urban trees’ cooling efficiency to ambient temperature remains largely unknown due to the complicated influences of ambient temperature on the physiological state of urban trees. In this study, we quantify the response of urban trees’ cooling efficiency to ambient temperature in 17 summers from 2003–2019 in 70 economically developed cities of China. The results show that the cooling efficiency of urban trees is enhanced with increasing ambient temperature, with values ranging from 0.002 to 0.055  per 1 ℃ increase in ambient temperature across the selected cities. This suggests additional cooling benefits provided by urban trees on hotter days, especially in cities with lower TCP levels. In addition, under the same TCP level, the additional cooling benefits are larger in warmer and wetter cities, as these cities have a sufficient water supply for urban tree transpiration. Finally, this study further confirmed that the enhanced cooling efficiency of urban trees on hotter days can additionally mitigate 3.64% of population exposure to urban heat stress. These results are expected to provide guidance for urban planners to alleviate urban heat risk by utilizing urban trees in a warming world.

How to cite: Yang, L., Ge, J., Cao, Y., Liu, Y., Luo, X., Wang, S., and Guo, W.: Enhanced cooling efficiency of urban trees on hotter summer days in 70 cities of China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1514, https://doi.org/10.5194/egusphere-egu24-1514, 2024.

Urban areas are faced with issues of particulate air pollution and urban heat islands, in a context of a growing number of their inhabitants. Ecosystem services provided by urban trees are impacted by the health and functioning mechanism of the trees, in particular the evapotranspiration process. The impact of urban specificities on tree functioning has yet to be fully studied. In recent years, improvement in remote sensing and the availability of very high spatial resolution imagery offer new perspectives and working methods for urban tree. The aim of this study is to explore how Pleiades imagery and field micro-dendrometer measurements can assess the health and water status of the two main tree species present in the city of Dijon: Acer Platanoides and Tilia Euchlora. The work has been leaded in 3 steps. First, the very high spatial resolution Pleiades imagery has been used to identify tree canopy in Dijon city. Generalist and empirical approaches are compared, for instance NDVI, MSAVI2 and EVI vegetation indices. Then, tree canopy, tree species (based on field records), morphological parameters (from topographic data and digital elevation model) and proximity to pollutant emissions are used to select six sites in Dijon. In each site, one or two mature trees (six Tilia Euchlora and five Acer Platanoides overall) are finally equipped with the micro-dendrometer (PepiPIAF system) to record daily stem diameter variations. Variables reflecting the water status of the trees, like the maximum daily shrinkage, are then calculated from these field measurements. The first results are encouraging, a marked response of vegetation indicators to precipitation is observed, with high values after heavy rainy episodes. The next step is to establish the link between vegetation indices obtain via remote sensing and micro-dendrometers measurements. This could in turn be a step forward the modelling of trees’ water status at a high spatial resolution at the scale of the city. 

How to cite: Canovas, L., Martiny, N., Bur, T., Marilleau, N., and Hartmann, C.: Assessing water status of two urban tree species : Acer Platanoides and Tilia Euchlora by very high spatial resolution imagery and field micro-dendrometers measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11301, https://doi.org/10.5194/egusphere-egu24-11301, 2024.

Urban trees experience a unique combination of stressors and environmental benefits from urban environments, which affect their physiological health and ability to deliver ecosystem service benefits. Understanding which tree species are resilient or vulnerable to extreme climatic events is crucial to managing a sustainable urban forest.

This study investigates species-specific variations in water fluxes of three popular urban tree species (Acer pseudoplatanus, Tilia europaea, and Betula pendula) in response to a high temperature event. We used sap-flow data from 12 trees in an urban woodland, collected from TreeTalker sensors within the University of Sheffield Urban Tree Observatory (UTO), a state-of-the-art urban tree sensor network in Sheffield, UK. Data were collected every hour over a 2-year period (2021-22), which included an extreme heatwave characterized by high atmospheric evaporative demands and lower rainfall. A significant decrease in sap-flow of ~30% was observed for A. psedoplatanus and T. europaea respectively in 2022 compared to 2021, following a 4-day extreme weather event with temperatures reaching 38.9^oC and Vapour Pressure Deficit (VPD) values of 5.8 kPa. B. pendula exhibited greater resilience to extreme climatic events with a ~5% decrease in sap-flow due to its low water demand. At the woodland scale, transpiration derived from sap-flow data was strongly correlated to evapotranspiration (ET) values from the ECOSTRESS Level 3 Instantaneous Evapotranspiration (ET_inst) satellite product under non-stressed conditions (R² =0.86; p<0.001). However, under stressed conditions during the heatwave event the relationship was much weaker (R² =0.38; p<0.05), which may be attributed to uncertainties in underlying ET algorithm.

This research elucidates the differing impacts of extreme weather conditions on three urban tree species and provides an assessment of their ability to continue to deliver ecosystem services. Whilst some caution should be exercised in interpreting ECOSTRESS ET data under temperature/water stress conditions, satellite technologies offer an exciting opportunity to remotely monitor water fluxes from trees in urban woodland at city-scales.

How to cite: Cunningham, S. T., Bryant, R. G., Khan, M. S., Caine, R. S., Edmondson, J., Absalom, E. C., Turner, A., Blackman, R., and Croft, H.: Modelling water fluxes from urban trees using ECOSTRESS and sap-flow data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12297, https://doi.org/10.5194/egusphere-egu24-12297, 2024.

The role of vegetation in urban climate has been in the spotlight in recent years, as it can play significant roles in carbon sequestration through photosynthesis as well as in the urban energy balance, mainly through evapotranspiration and shading. Based on these, the green infrastructureof cities is considered as a potential solution to lower the urban net CO2 exchange and lower air temperatures, improving the resilience of cities in the context of climate change.Being part of the general physiological responses of trees, the abovementioned mechanismshave been excessively studied in natural environments. However, the quantification of the different effects of these processes in complex and heterogeneous urban landscapes is challenging. In this study, we demonstrate initial results of a year-long observation period of tree vegetation in a residential area in Berlin, Germany, using PhenoCam and flux-tower observations. The phenology curves were extracted from half-hourly PhenoCam images of trees from the Acer, Aesculus, Fagus, and Pinus genera and analysed in combination with comprehensive observations of  thesurface energy balance components, including net radiation, turbulent sensible and latent heat fluxes as well as CO2 fluxes and standard meteorological variables. We showcase the agreement between the gradual development of tree foliage fordeciduous vegetation (which dominates the area) with: a) the upward latent heat flux seasonal maxima observations; and b) the decline of upward CO2 flux values. In particular, the timing of the start of season (SOS), peak of season (POS) and end of season (EOS) is assessed and compared to changes detected in the flux trends. Our data indicates a strong connection of the green-up period of deciduous vegetation with the largest rate of decrease of the CO2 fluxes, leading to a change from CO2 source to sink for a constrained time period. These observations highlight the measurable effect of vegetation-related carbon sequestration that can take place in urban areas with significant vegetation cover under specific/average meteorological conditions.

How to cite: Tsirantonakis, D., Looschelders, D., Fenner, D., Meier, F., Chrysoulakis, N., Christen, A., Grimmond, S., and Birkmann, J.: Urban trees phenology and local climate feedbacks of a residential area in Berlin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15395, https://doi.org/10.5194/egusphere-egu24-15395, 2024.

Remote sensing for vegetation monitoring can involve mixed pixels with contributions from vegetation and background surfaces, causing biases in signals and their interpretations. This is especially so in cases when remote sensing applications are deployed in conditions with sparse vegetation, such as trees in urban areas, where multiple components within a pixel need to be considered; in such cases, the contained spectral information can be difficult to interpret.

A ground-based experimental layout consisting of a spectrometer and a thermal camera mounted on a portable crane for assessing the optical and thermal signatures of the tree canopy - underlying surface system, was deployed in a controlled field experiment. Two groups of five identically arranged containerised Acer platanoides 'Columnare' were placed into two adjacent built and non-built local microenvironments. Using the obtained thermal signatures, the relative contribution of the underlying surface and tree canopy to the overall spectral reflectance variation was examined.

A moderate correlation between the canopy-background temperature difference and the spectral reflectance for the built local microenvironment indicates that the synergy between thermal and spectral measurements in the fine scale is a promising method for disentangling the combined signal components. Further results will be presented in the conference.

How to cite: Halios, C., Haghparast, Y., Smith, S., Pickles, B., Shao, L., and Mortimer, H.: An experimental study of the tree canopy-urban surface system optical and thermal signatures , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13161, https://doi.org/10.5194/egusphere-egu24-13161, 2024.

Trees have a pivotal role in mitigating heat island effects and several studies analyzed temperature differences of various species. However, the potential of trees to decrease temperatures during heat waves, drought and extreme events is inadequately studied, particularly at the city scale. Therefore, we present a remote sensing based approach that evaluates surface temperatures of trees in the urban environment of Forchheim (Germany) during the heatwave 2022. To provide an example of extreme conditions, we conducted measurements on July 20, 2022, the day with the current absolute daily heat record of the region since temperature measurements started in 1949. The three-month period before the survey flight (May-July) was the second warmest and third driest May-July period ever measured, leading to an ideal setting to assess the role of trees in urban regions during projected climate extremes. Analyzing such situations is highly relevant for city planning as existing research showed that sap flow is only reduced after several weeks of drought. We performed a low-altitude flight campaign (350 meters above ground) during the daily maximum temperature period (2-4 pm) with a thermal camera (Optris PI 450) for surface temperatures and a multispectral camera (Micasense RedEdge M) for vegetation parameters and land cover. We compared derived surface temperatures at field mapped locations of more than 3000 trees covering more than 30 species (n ≥ 20) to assess species patterns and the influence of urban parameters such as imperviousness. We show differences between species and interrelationship with vegetation parameters (e.g. NDVI) to provide insights into mitigation effects and patterns of urban trees during extreme events.

How to cite: Zandler, H. and Samimi, C.: Remote sensing based analysis of urban tree temperatures during extreme heat and drought, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5086, https://doi.org/10.5194/egusphere-egu24-5086, 2024.

Urban trees are essential as they provide services in terms of air pollution mitigation, freshness, biodiversity, and citizens’ well-being. Accurate data on location, species, and structural characteristics are essential for quantifying tree benefits. For a realistic and proper quantification of the benefits of urban vegetation in terms of providing ecosystem services at city scale, a consistent inventory of vegetation within residential and public areas, is needed. However, the cost of measuring thousands of individual trees through field campaigns can be prohibitive and reliable information on domestic gardens is lacking due to difficulties in acquiring systematic data.

The main objective of this study was to investigate the suitability of very-high resolution satellite imagery for detecting, delineating, and classifying the dominant plant species in both public and private urban areas. The detection of individual trees and species differentiation are challenging in cities, as trees can be isolated, lined up or grouped in patch, with a wide range of plant species, high spectral similarity of vegetation types, and high-density stands, trees in the shade, trees with low spectral contrast, and due to the complexity of the urban environment (buildings, shadows, open courtyards). To overcome these constraints, a canopy-based classification was developed with the selection of new relevant spectral and texture-based features for each tree species and herbaceous areas.

A pan-sharpening approach and stepwise masking protocol from WV-2 imagery were used to separate vegetated and non-vegetated areas, tree, and non-tree canopy, over the study areas prior to tree species mapping. The shadows of the trees, but also the shadows of the objects (e.g., buildings) were correctly removed within residential yards. Then, we performed a multispectral procedure of object-based classification using Random Forest classifier with different textural features extracted from tree canopy and grassland (lawn/turf) to identify and map dominant types of vegetation. Four spectral bands (blue, green, yellow, red) and four texture features (i.e., energy, entropy, inverse difference moment, Haralick correlation) were found to be the most efficient attributes for canopy-based classification from WV-2 images.

In both study areas, about 420,000 and 555,000 canopies were successfully classified in Aix-en-Provence and Florence with about 85% in private lands and not under municipalities supervision. We also detected 1,157 and 5,438 herbaceous areas in Florence and Aix-en-Provence, respectively. The number of canopies not classified is very low, i.e., 66 out of 419,399 tree canopies were not classified in Aix-en-Provence (< 0.02%) and 4,030 out of 554,603 tree canopies in Florence (< 0.7%). In the two study areas, Aix-en-Provence (France, 50km²) and Florence (Italy, 80km²), 22 and 20 dominant species were identified and classified with an overall accuracy of 84% and 83%, respectively. The highest classification accuracy was obtained for Pinus spp. and Platanus acerifolia in Aix-en-Provence, and for Celtis australis and Cupressus sempervirens in Florence.

How to cite: Coulibaly, F. and Sicard, P.: Canopy-based Classification of Urban Vegetation from Very High-Resolution Satellite Imagery, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-583, https://doi.org/10.5194/egusphere-egu24-583, 2024.

Trees have a strong effect on the local wind climate. To better understand their impact, an accurate and detailed reconstruction of botanical trees into digital twins from terrestrial LiDAR scan point clouds is important. However, capturing the complex, multi-scale nature of tree structures poses significant challenges. Issues such as gaps in the model due to occlusion in the point cloud data and inaccuracies in branch thickness estimations — especially for smaller branches — are prevalent limitations. Most advanced reconstruction methods today, such as TreeQSM (Raumonen et al., 2013), have been primarily designed for forestry applications, such as volume and biomass estimation. However, numerical flow simulations pose additional requirements including the need for a closed and continuous surface.

This study introduces a different approach, building upon the work of Bærenzten et al., 2023, using tools from the field of computer graphics. The proposed method initially creates a graph from the point cloud by connecting nearby points. Subsequently, a highly detailed skeleton of the tree is generated using the so-called local separators approach (Bærenzten et al., 2021). Local separators are defined as collections of vertices that are contained within a sub-graph of the original graph. The removal of a local separator splits the sub-graph into multiple smaller sub-graphs. The branch diameters are subsequently determined using a hybrid method that blends data-driven estimates derived from the point cloud data with the Da Vinci rule for trees, which defines a relationship between the diameters of a mother branch and its daughter branches. Additionally, species-specific data obtained from direct diameter measurements is incorporated in the estimation process. The tree’s surface is then reconstructed by first generating an implicit representation from which a closed mesh is extracted as an iso-surface.

Through a parameter study, the two main parameters for the generation of the skeleton, as well as the two main parameters influencing the branch thickness estimation, were studied in detail. The algorithm effectively handles occlusion in the point cloud, producing fully connected branching structures. The combined approach notably enhances the branch thickness estimation compared to using only one approach. We demonstrate the robustness of the method by applying it to three trees of very different dimensions, complexities, and point cloud characteristics and outline how the finally reconstructed tree will be used in atmospheric flow simulations.

References

Raumonen, P., Kaasalainen, M., Åkerblom, M., Kaasalainen, S., Kaartinen, H., Vastaranta, M., Holopainen, M., Disney, M., & Lewis, P. (2013). Fast Automatic Precision Tree Models from Terrestrial Laser Scanner Data. Remote Sensing, 5, 491-520. https://doi.org/10.3390/rs5020491

Bærentzen, J. A., Villesen, I. B., & Dellwik, E. (2023). Reconstruction of a Botanical Tree from a 3D Point Cloud. In E. Christiani, M. Falcone, & S. Tozza (Eds.), Mathematical Methods for Objects Reconstruction: From 3D Vision to 3D Printing (Vol. 54, pp. 103-120). Springer. https://doi.org/10.1007/978-981-99-0776-2\_4

Bærentzen, A., & Rotenberg, E. (2021). Skeletonization via Local Separators. ACM Transactions on Graphics, 40(5), Article 187. https://doi.org/10.1145/3459233

How to cite: Pabst, H. A., Bærentzen, A., Morales, A., MacFarlane, D., and Dellwik, E.: Digital Tree Twins: Detailed Reconstruction from Point Clouds using a Skeletonization Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8878, https://doi.org/10.5194/egusphere-egu24-8878, 2024.

Urban trees are essential for cities as they reduce the risk of flooding and provide shade and coolness in the summer months. However, these trees are exposed to environmental stresses, e.g. due to limited soil resources and unfavorable hydrological conditions caused by impervious surface and drought. As part of the CliMax project, our research aims to develop a method that uses LiDAR (light detection and ranging) and Sentinel-2 to monitor and estimate the vitality of urban trees in Braunschweig and Brandenburg a.d.H. Estimating urban tree vitality by conducting ground measurement requires a huge number of work force and resources, which is expensive and time consuming. Remote sensing enables continuous monitoring of trees within the urban area.

In this research, we implemented a four-step methodology to detect individual urban trees based on airborne LiDAR data. Firstly, a pre-classified subset of the upcoming digital twin LiDAR data (harmonized Germany-wide data) was used to train a machine-learning model. This model is designed to distinguish between trees and buildings by relying on geometric features describing the three-dimensional LiDAR point distribution, such as planarity, sphericity or verticality. Secondly, the LiDAR data was rasterized into a Canopy Height Model (CHM) to delineate single trees by applying the slope break technique. We modified the conventional slope break computation to counteract the underestimation of the crown diameters. Third, the slope break values defined the different window sizes for the Local Maximum Filter (LMF) used to determine the spatial position of the treetops. Fourth, the extracted treetops were used as seeds in a watershed segmentation to partition a CHM into individual tree polygons based on the topology of its intensity surface.

We tested our method on a subset with heterogeneous landscape elements (park, building, and street) in Braunschweig and used tree cadastral data – provided by city authorities - for validation. The tree cadastre documents the location, height and crown diameter of each tree based on on-site surveys. With that, we evaluated the performance of our individual tree detection procedure and achieved a commission error of 36.72% and an omission error of 5.41%. A comparison of the cadastral data with the remotely sensed derived parameters results in an R² of 0.246 and 0.7452 for the crown diameter and tree height respectively.

Sentinel-2 data from June 2023 served as the basis for calculating the Normalized Difference Vegetation Index (NDVI), which we initially used as proxy for tree vitality. Additionally, we calculated the percentage of fraction tree cover per Sentinel-2 pixel. We found that pixel’s tree cover correlates with the average NDVI values, but individual observations are often influenced by the tree's understory, resulting in higher NDVI values. In the next step, we will evaluate NDVI time series for the vitality analysis of urban trees and investigate pixel’s spectral components in more detail.

How to cite: Shrestha, N., Preidl, S., and Golla, B.: Remote sensing data (LiDAR, Sentinel-2) to detect individual urban trees and determine a vitality index, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18803, https://doi.org/10.5194/egusphere-egu24-18803, 2024.