Threshold Behaviour and Design Controls on Tree Uprooting during Pluvial Flood Events: A Hybrid AI and Experimental Flume-Based Study

While Singapore has demonstrated concerted efforts and progress in pluvial flood management, the recent Third National Climate Change Study in Singapore (V3) projects an increase in future annual extreme rainfall, and flash floods are expected to intensify. However, occurrences of flash floods in Singapore generally do not result in fatalities and significant infrastructural damages, and the most salient impacts observed during flash flood events are disruptions to traffic networks and businesses, which translates to economic and productivity losses.This study thus aims to 1) Characterise future flooding likelihood and its uncertainties in Singapore under various Shared Socioeconomic Pathways (SSPs) for mid and end-century scenarios, 2) Calculate potential economic loss associated with travelling time delay due to traffic disruptions during flood events.A Bayesian probabilistic modelling approach was used to obtain the probability distribution of flooding as a function of various precipitation intensity values (i.e. maximum 30, 60, and 120 minutes rainfall) for present day and across different SSPs scenarios. Travel routing simulations of vehicle and public transit were conducted for dry and flood conditions to determine the total travel time delay during flood conditions.Results showed that future flood likelihood is the highest and has the most widespread impacts beyond the 99th percentile of maximum 30 minutes rainfall, compared to other intense rainfall durations. Interestingly, flooding likelihood is higher for present conditions than future scenarios due to projected longer drier days and more intense but infrequent extreme precipitation.Intensification of precipitation extremes in the future poses hard limits to pluvial flood prevention in Singapore, which has significant implications to policy. This indicates that continual infrastructural flood prevention measures have limited efficacy under extreme rainfall events, and cross-sectoral adaptation measures for extreme rainfall and pluvial flooding should be prioritised to enhance flood resilience in Singapore.

This paper deals with the results of the Research Project “METROPOLIS – Integrated and sustainable methods and technologies for resilience and safety in urban systems”, funded under PONREC 2007-2013. Among all the results of the work, the paper is focused on the development of a model to measure climate vulnerability in urban areas. The application of the model provides the assessment of impacts and the subsequent planning of corrective actions to increase building and urban resilience by means of technological retrofitting. The testing of the model for heat waves and pluvial flooding has been implemented in the urban system of Naples City which has been divided into the physical subsystem and the population subsystem.

Modelling green roof stormwater response for different soil depths

Low-lying coastal cities across the world are vulnerable to the combined impact of rainfall and storm tide. However, existing approaches lack the ability to model the combined effect of these flood mechanisms, especially under climate change and sea level rise (SLR). Thus, to increase flood resilience of coastal cities, modeling techniques to improve the understanding and prediction of the combined effect of these flood hazards are critical. To address this need, this study presents a modeling system for assessing the combined flood impact on coastal cities under selected future climate scenarios that leverages ocean modeling with land surface modeling capable of resolving urban drainage infrastructure within the city. The modeling approach is demonstrated in quantifying the impact of possible future climate scenarios on transportation infrastructure within Norfolk, Virginia, USA. A series of combined storm events are modeled for current (2020) and projected future (2070) climate scenarios. The results show that pluvial flooding causes a larger interruption to the transportation network compared to tidal flooding under current climate conditions. By 2070, however, tidal flooding will be the dominant flooding mechanism with even nuisance flooding expected to happen daily due to SLR. In 2070, nuisance flooding is expected to cause a 4.6% total link close time (TLC), which is more than two times that of a 50-year storm surge (1.8% TLC) in 2020. The coupled flood model was compared with a widely used but physically simplistic bathtub method to assess the difference resulting from the more complex modeling presented in this study. The results show that the bathtub method overestimated the flooded area near the shoreline by 9.5% and 3.1% for a 10-year storm surge event in 2020 and 2070, respectively, but underestimated the flooded area in the inland region by 9.0% and 4.0% for the same events. The findings demonstrate the benefit of sophisticated modeling methods compared to more simplistic bathtub approaches, in climate adaptive planning and policy in coastal communities.

This paper applies an Adaptation Tipping Point (ATP) approach for the assessment of vulnerability to flooding in the city of Dhaka, Bangladesh. A series of rigorous modelling exercises for fluvial and pluvial flooding was conducted to identify the critical ATPs of the physical system, under both existing and proposed flood risk management strategies, for different urban and climate change scenarios. But a standalone assessment of the physical system’s ATPs is insufficient to gain a complete understanding of flood risks; community resilience also depends on people’s adaptability and the acceptance of risks by the community in question. Through participatory public consultations, this study determines the critical ATPs for community risk acceptance. The concept of the “Integrated Adaptation Tipping Point (IATP)”, introduced here, combines the accepted level of risk to the community with the ATPs for physical systems. This approach reveals that the assessed vulnerability to flooding increases when social tipping points are considered.

Urban trees are sensitive to extreme weather events under climate change. Freeze-thaw induced hydraulic failure could induce urban tree dieback and nullify the services they provide. Plant height is a simple but significant trait for plant ecological strategies. Understanding how urban trees with different heights adapt to freeze-thaw stress is increasingly important under climate change. We investigated the relationship between tree height and stem hydraulic functional traits of six common urban tree species in North China to explore tree height-related hydraulic strategies to cope with freeze-thaw stress. Results showed that tall trees had wider vessels, higher hydraulic conductivity, more winter embolism, but lower vessel and wood densities. Positive relationships were found between tree height and vessel diameter, hydraulic conductivity, and freeze-thaw induced embolism, and negative relationships were found between tree height and vessel and wood densities, which implied that short trees employ more conservative ecological strategies than tall trees. Tall and short tree species were well separated by multiple stem hydraulic functional traits; this is consistent with the fact that tall and short trees occupy different niches and indicates that different hydraulic strategies for freeze-thaw stress exist between them. Tall trees might face more pressure to survive under extreme cold weather caused by climate change in the future. Therefore, more attention should be paid to tall urban tree management in North China to cope with extreme cold weather.

By 2050, nearly 70% of the global population will live in cities (UN, 2018), increasing the demand for urban green spaces. Urban areas are facing increasing risks from climate change, including heatwaves, flooding, wildfires, and growing social inequality, which challenges urban planning and design. Urban forests form the backbone of green infrastructure supporting resilient, equitable, and sustainable cities. Importantly, their cost-effective benefits advance sustainable development, climate action, and biodiversity conservation. Urban forests include all woody and understorey vegetation within and around dense settlements, from cultivated trees in streets, parks, and gardens to self-sustaining stands in remnant and peri-urban woodlands (FAO, 2016). As essential nature-based solutions (Cohen-Shacham et al., 2016), urban forests provide multiple ecosystem services. They help cool urban temperatures, reduce air pollution, enhance soil infiltration, slow stormwater runoff, buffer extreme weather, and support human health (Livesley et al., 2016). They contribute significantly to climate adaptation and moderately to mitigation by reducing the energy demand for cooling (McPhearson et al., 2023). Urban forests also enhance biodiversity by providing habitats and climate refugia at multiple scales (Alvey, 2006). Trade-offs in urban forest benefits, costs, and the impacts of policy interventions, such as those related to measurement, outcomes, or implementation, remain complex (Vogt et al., 2015), but the loss of canopy reduces air quality, biodiversity, and resilience to floods, droughts, pests, and extreme heat (Nowak, 2018). Canopy loss impairs recreation and impacts physical and mental health (Carrus et al., 2015). Because urban forests are inherently dynamic systems, the death or removal of large and mature trees should be anticipated through proactive planning for their replacement, including careful consideration of which species are selected and why. Unequal access drives social-environmental injustice and health inequities, which can be addressed through greenspace expansion, equitable distribution, and better management (Esperon-Rodriguez et al., 2025). Urban forests are increasingly at risk due to significant stewardship gaps. Despite the existence of international management standards, ongoing tree losses result from pests introduced through trade, climate and pollution stress, inadequate legal protections, rapid urban densification, and insufficient maintenance (Esperon-Rodriguez et al., 2022; Paap et al., 2017; Vogt et al., 2015). Planting alone cannot offset accelerated mature tree losses or replace the vital functions these trees provide over their shortened lifespans in urban environments. Closing the stewardship gap demands urgent investment, robust funding, and stronger policy to sustain diverse and resilient urban forests. Urban forests are among the most effective, equitable nature-based solutions available. When protected and resourced, they cool neighborhoods, manage stormwater, store carbon, support biodiversity, and improve health, especially in underserved communities. Yet mature tree loss outpaces replacement amid increasing climate and biological stresses. We urge COP30 policymakers to treat urban forests as essential and critical city infrastructure: safeguard mature trees, set and finance SMART canopy, diversity and access targets, mainstream urban forests in climate and biodiversity plans, and fund long-term operations, monitoring, nursery capacity, and biosecurity. Implementing this visionary action delivers cooler, healthier, more biodiverse, and more equitable cities now and for future generations. MER and MGT led the initiative and drafted the letter. All authors provided feedback, edited, and agreed with the content of the letter. All authors, except MER and MGT, are listed alphabetically. MER received funding from Western Sydney University's Research Theme Program. KDP was supported by the Research Foundation Flanders (FWO, grant 12A0L25N). RMM was supported by a Discovery Early Career Researcher Award (project DE200100649), funded by the Australian Research Council of the Australian Government. JCS received funding from the Danish National Research Foundation (grant DNRF173) and EARTHKEEPER (Global South Biodiversity Leadership Initiative). CS's contribution was funded by the National Research Foundation of South Africa (grant no 84379). We declare no conflict of interest. There are no data associated with the article.

Spatial estimation of urban forest structures with Landsat TM data and field measurements

With the rapid acceleration of global urbanization, Urban Sustainability and Resilience (USR) have emerged as pivotal issues in addressing resource scarcity, environmental degradation, and extreme climate challenges. Focusing on this context, this study investigates whether the National Forest Cities Construction (NFCC) policy promotes urban sustainability and resilience and examines how human capital (HC), artificial intelligence (AI) and government support (GS) mediate these effects. This study evaluates the impact of National Forest Cities Construction (NFCC) policies on USR using panel data from 300 Chinese cities from 2000 to 2023. Employing a multi-period Difference-in-Differences (DID) approach and constructing an entropy-weighted TOPSIS evaluation framework, we systematically assess the policy effects on urban economic, social, and environmental coordination and risk response capacities. Our findings reveal a significant positive impact of NFCC policies on overall USR, with pronounced heterogeneous effects observed across regions and city scales—most notably, policies exhibit the strongest effects in eastern regions and are particularly sensitive among small-to-medium-sized cities. Further mechanism analyses identify three intrinsic transmission pathways: Human Capital (HC), Artificial Intelligence (AI), and Government Support (GS). Although the HC channel initially displays a negative adjustment effect, the gradual accumulation of skilled talent significantly enhances its positive influence over time. In contrast, while the AI channel effectively promotes intelligent technology adoption, it negatively affects Urban Sustainability (US) yet positively contributes to Urban Resilience (UR). The GS channel significantly increases public financial investment and environmental governance; however, inefficiencies in resource allocation yield negative transmission effects on both US and UR. These empirical insights clarify the effectiveness of NFCC policies and their regional and scale-specific differences, offering practical recommendations for policy optimization and governance strategies. Ultimately, this study provides a robust theoretical and empirical foundation for advancing high-quality urban development characterized by integrated economic growth, environmental protection, and risk management.

Trees provide a broad amount of ecosystem services in urban areas. Although it is well documented that trees are essential for the well-being and livability of cities, trees are often not evenly distributed. Studies have found that urban residents with a deprived socioeconomic status are associated with a lower coverage and access to urban trees in their communities, yet a fair distribution of trees contributes to the sustainability and resilience of cities. In this context, the environmental justice movement seeks to ensure equal distribution of green infrastructure and its benefits throughout a territory. The objective of this study is threefold: (i) to determine whether urban trees in Guadalajara, Mexico, are distributed equally; (ii) to assess the association between urban trees and socioeconomic status; and (iii) to introduce compositional data analysis to the existing literature. Due to the compositional nature of the data, compositional analysis techniques are applied. We believe this novel approach will help define the proper management of data used in the literature. The outcomes provide insights for urban planners working towards the Sustainable Development Goals to help eradicate the uneven distribution of urban trees in cities.

This research investigated the historical changes in basin-scale rainfall characteristics and their spatial distributions in the Lake Biwa and Yodo River Basin. Nine rainfall indices including two general and seven extreme rainfall indices and the probable rainfall according to 50- and 100-year return periods were evaluated based on the data gathered from 61 rain gauge stations. The regionalization of the rainfall indices and probable rainfall was then examined using spatial interpolation via the Kriging method. The results of the spatial analysis for the rainfall indices showed that there is a potentially high risk of extreme rainfall events and pluvial floods, particularly in the northern, western, and southern areas. The 50- and 100-year probable rainfall has historically increased in the north through to the western area of the basin. The return periods of the 50- and 100-year rainfall events decreased in the northern area of Lake Biwa and the western area of the basin. The findings of this research suggest that the local flood management plan needs to be updated depending on the regional differences in extreme rainfall characteristics. In basins/areas with sparsely distributed rain gauge stations, regionalization can provide useful information as part of local flood management planning.

The impact of land use- and climate change on the managed eco-geomorphic balance in the Alps

Abstract. Mosyaftiani A, Wahyu A, Kaswanto, Wiyoga H, Syasita N, Septa AF, Djauhari D. 2022. Monitoring and analyzing tree diversity using i-Tree eco to strengthen urban forest management. Biodiversitas 23: 4033-4039. Inadequate data on vegetation growth makes it difficult for managers to determine the additional measures necessary for effective urban forest management. The management of urban forests in Jakarta also raises this issue. Collaborative research with multiple stakeholders was conducted in five Jakarta urban forests to assess the diversity and structure of the vegetation as a basis for long-term monitoring and management. Using 49 plots, we carried out a field inventory to gather information on tree number, diameter at breast height, tree height, and crown size. The i-Tree Eco programme was used to examine the data and information gathered. The widely used i-Tree Eco analysis was conducted to make viable evidence-based evaluation feasible and to help stakeholders with data processing. The results showed that the five urban forests had a moderate level of diversity, with an index value ranging from 2.1 to 3.0. The five most common tree species—Swietenia macrophylla, Terminalia sp., Delonix regia, Ceiba pentandra, and Aleurites moluccanus—dominate urban forests, whereas three of them are exotic and most native species have substantially lower values. Increasing tree diversity by enriching native species is recommended to be a top priority for urban forest management in Jakarta. Additionally, this research shows that adopting advanced and user-friendly tools to regularly monitor and analyze vegetation helps stakeholders achieve better urban forest management.

<p>Despite the widespread concerns of increasing precipitation extremes caused by climate change, the application of urban trees as a nature-based solution against pluvial flooding are still often overlooked and undervalued due to its limited practical value in case of extreme rainfall occurrences. Hence, this study investigated the rainfall interception performance of open-grown birch (<em>Betula pendula Roth.</em>) and pine (<em>Pinus nigra Arnold</em>) trees in an urban park of Ljubljana, Slovenia (Europe) on an event basis using disdrometer data. In addition, we closely analysed the rainfall microstructure under both types of trees during the extreme storm event on September 29, 2021 and compared it to average values from the past. During this single storm event with a cumulative rainfall of 87.6 mm within 7.6 hours, birch trees intercepted 19.5% of the gross rainfall, which is lower than its average interception of 35.9% during the period of 2014-2017. On the other hand, the canopy of pine trees was able to intercept 47.0% of rainfall – higher than its average retention capacity of 37.1% during extreme events in the past (>40 mm). The total number of raindrops recorded for this event under the birch tree crown is 362,556 with a largest diameter of 13 mm, where the throughfall from birch and pine trees constitute 75% and 53% of the rainfall, respectively. For small to moderate rainfall events that occurred from August to October 2021 with an average number of 167,329 raindrops, the amount of rainfall intercepted by birch and pine tree canopies corresponds to 23.8% and 55.7%, respectively. The results show that on an event basis, both types of trees perform effectively in intercepting low to medium magnitudes of precipitation. Results also reveal that pine trees can intercept substantially more rainfall even during the high-magnitude events, which emphasizes the importance of proper selection of trees species with higher rainfall interception capacity to leverage its benefits in an urban setting during extreme conditions.</p><p>Acknowledgments: Results are part of the CELSA project entitled “Interception experimentation and modelling for enhanced impact analysis of nature-based solution” and research programme P2-0180 supported by the Slovenian Research Agency (ARRS).</p>

Trees play a vital role in the urban ecosystem, providing benefits for society, ecology and economy. In particular in urban areas, trees mitigate the urban heat island effect, filter air pollution, regulate microclimate and hydrology, bond carbon dioxide, and provide spaces for recreation and leisure, among others. Despite these diverse positive effects, detailed information on the number, location, dimensions and other characteristics of urban trees remains scarce. For this reason, most cities in Germany currently aim to establish a tree information system for efficient and targeted management of their tree inventory. However, traditional terrestrial surveying is time-consuming and costly and therefore only suitable to a limited extent. In addition, the municipal tree cadastre usually only includes urban trees on public propertyand thus does not cover the complete stock. Against this background, remote sensing acquisitions with very-high spatial resolution (VHR) of less than one meter offer promising capabilities for area-wide detection, delineation, and characterization of urban trees. In this study, we use VHR aerial imagery as well as a derived canopy height model (CHM) for detection and delineation of urban trees. Different methods for individual tree detection using local maximum (LM) filtering andLaplacian of Gaussian (LoG) blob detectionare compared and evaluated. For tree crown delineation, marker-controlled watershed segmentation (MCWS), clustering using Voronoi tessellation, and region growing are implemented as segmentationtechniques. The detection of individual trees and delieation of tree crowns are validated against about1,000 reference trees from visual interpretation via stereophotogrammetry.In addition, we relate our results to street tree location data of Munich, which was derived from mobile terrestrial laser scanning (TLS).The characterization of urban trees is realized based on the 3-dimensional shape of individual tree segments as well as auxillary data sets of land use and building density. According to our analyses, there are 1.54 million trees in Munich.Compared to available reference trees, tree detection was evaluated with highest values of F-score, precision, and recall of 0.95, 0.99, and 0.94, respectively. Results of tree crown segmentation revealed an overall accuracy of 88.1 % compared to crowns of reference trees. Based on auxillary land use information, urban trees were categorized into street trees, (public) park trees, as well as trees in (private) residential gardens.In Munich, 9.1 % are characterized as street trees, 38.4 % are allocated in residential gardens and 33.1 % stand in public parks. The remaining 19.4 % oftree segments were found onother land use such as agricultural areas, parking lots, or along railroad tracks. According to these categories, the height and crown area of urban trees are analyzed and related to the distance to the city center. In a more general manner, this analysis was performed in relation to the building density in Munich. As expected, relatively few trees were found close to the city center and generally on areas with high building density. However, these areas are particularly associated with the greatest challenges in the context of sustainable and climate change-adapted urban development.In this study, we demonstrate that information derived from remote sensing contributes new spatial and quantitative knowledge on urban trees, providing the basis for sustainable management and informed decision-making in cities.