Soil surface temperatures reveal moderation of the urban heat island effect by trees and shrubs

Is urbanization a driver of aboveground biomass allocation in a widespread tropical shrub, Turnera subulata (Turneroideae - Passifloraceae)?

Plant biomass allocation is mainly affected by the environment where each individual grows. In this sense, through the rapid global expansion of impermeable areas, urbanization has strong, albeit poorly understood, consequences on the biomass allocation of plants found in this environment. Nevertheless, the comprehension of biomass allocation processes in urban shrubs remains unclear, because most studies of urban ecology focus on tree species. This is an important gap of knowledge because a great part of urban vegetation is composed of shrubs and their association with trees have positive impacts in urban ecosystem services. In this study, we explored the ecological and potential selective pressure effects of an urbanization gradient on the biomass allocation patterns of aboveground organs of Turnera subulata, a widely distributed tropical shrub. We have demonstrated that, for certain reproductive organs, biomass allocation decreases in locations with higher urbanization. Unlike expected, the biomass of vegetative organs was not affected by urbanization, and we did not observe any effect of urbanization intensity on the variance in biomass allocation to vegetative and reproductive organs. We did not record urbanization-mediated trade-offs in biomass allocation for reproductive and vegetative organs. Instead, the biomass of these structures showed a positive relationship. Our data suggest that urbanization does not result in radical changes in biomass allocation of T. subulata, and neither in the variation of these traits. They indicate that the ability of T. subulata to thrive in urban environments may be associated with life history and morphological mechanisms. Our findings contribute to the understanding of shrub plant responses to urbanization and highlight urbanization as a potential factor in resource allocation differences for different structures and functions in plants living in these environments.

Land surface temperature and transboundary air pollution: a case of Bangkok Metropolitan Region

In a rapidly urbanizing world, heavy air pollution and increasing surface temperature pose significant threats to human health and lives, especially in densely populated cities. In this study, we took an information theory perspective to investigate the causal relationship between diel land surface temperature (LST) and transboundary air pollution (TAP) from 2003 to 2020 in the Bangkok Metropolitan Region (BMR), which includes Bangkok Metropolis and its five adjacent provinces. We found an overall increasing trend of LST over the study region, with the mean daytime LST rising faster than nighttime LST. Evident seasonal variations showed high aerosol optical depth (AOD) loadings during the dry period and low loadings at the beginning of the rainy season. Our study revealed that TAP affected diel surface temperature in Bangkok Metropolis significantly. Causality tests show that air pollutants of two adjacent provinces west of Bangkok, i.e., Nakhon Pathom and Samut Sakhon, have a greater influence on the LST of Bangkok than other provinces. Also, the bidirectional relationship indicates that air pollution has a greater impact on daytime LST than nighttime LST. While LST has an insignificant influence on AOD during the daytime, it influences AOD significantly at night. Our study offers a new approach to understanding the causal impact of TAP and can help policymakers to identify the most relevant locations that cause pollution, leading to appropriate planning and management.

Soil Black Carbon Increases Under Urban Trees with Road Density and Time: Opportunity Hotspots for Carbon Storage in Urban Ecosystems

Black carbon (BC) can comprise a significant fraction of the soil carbon pool in cities. However, vegetation cover and human activity influence the spatial distribution of urban soil BC. We quantified soil total carbon (TC), soil organic carbon (SOC), BC, and total nitrogen (TN) in a medium-sized city in Dallas-Fort Worth, Texas. Soils were sampled to 20 cm depth from underneath 16 paired Quercus stellata (post oak) trees and open lawns. Effects of vegetation cover, road density, and building age (a proxy for time since development) on soil C and N were analyzed. Soil OC concentrations were higher under post oak trees (5.5%) compared to open lawns (3.6%) at 0-10 cm, but not at 10-20 cm depth. In contrast, soil BC and TN did not differ by vegetation cover. There were significant interaction effects between vegetation cover and road density and vegetation cover and building age on soil BC. At 0-10 cm, soil BC concentrations, stock, and BC/SOC ratios increased more with road density under trees than lawns, indicating enhanced atmospheric BC deposition to tree canopies. Black carbon in tree soils also increased with building age as compared to lawn soils, likely due to higher BC retention under trees, enhanced BC losses under lawns, or both. Our findings show that urban tree soils are localized opportunity hotspots for BC storage in areas with elevated emissions and longer time since development. Conserving and planting urban trees above permeable surfaces and soils could contribute to long-term carbon storage in urban ecosystems.

Spatio-temporal evolution of land use and its eco-environmental effects in the Caohai National Nature Reserve of China

With the rapid development of social economy, the ecological environment problems caused by the change of wetland land use have been widely concerned. This paper takes the Caohai National Nature Reserve (CNNR) of China as the research object on the basis of referring to previous research results. Firstly, the remote sensing data was employed to examine the spatio-temporal evolution process of the CNNR from three aspects: land use structure change, land use dynamic degree and land use space change. Then the change of ecological environment quality was studied from the greenness, the wetness, the dryness and the heat. Based on the spatiotemporal changes of land use types and ecological environment quality in the CNNR from 2000 to 2020, a comprehensive index, the remote sensing ecological index (RSEI), was constructed to analyze the ecological environmental effects of land use changes. The results indicate that the land use changes in the CNNR went through two major periods: first, a period of rapid decline in cultivated land, and second, a period of sharp increase in constructed land. During the period of rapid decline in cultivated land, the ecological environment quality in the study area showed an upward trend. However, during the period of increased constructed land, the ecological environment quality gradually stabilized. This study provides a basis for the coordinated development of the ecological environment and social economy in the CNNR area.

Cooling effect of urban forests on the urban heat island in Seoul, South Korea

Air pollution and climate change amplify the urban heat island (UHI) effect, which has an adverse effect on human health. Urban forests (UFs) are important to reduce the UHI effect; however, the quantitative effect of UFs on UHI, relative to time and space, has not yet been investigated. In this study, we aimed to quantitatively measure the actual thermal environment in UFs. To this end, temperature and humidity loggers were installed in 17 UFs in Seoul for a year and analyzed according to vegetation characteristics and accessibility. The urban forests and park showed consistent temperature reduction, whereas the lawn showed higher temperature reduction effects during autumn-winter. The traffic island showed lower annual temperature reduction effect than other UFs. From spring to autumn, mixed and broadleaved forests showed better temperature reduction effect than coniferous forests. The temperature in UFs decreased by approximately 1.9°C over ~3 km from the traffic island near the city to the forest. This study revealed the difference in the cooling effect according to the type and location of UF and the vegetation structure. The functional characteristics of plants and the UF that reflects them can help reduce the negative impact of climate warming and UHI on human health.

Beyond Cleansing: Ecosystem Services Related to Phytoremediation

Phytotechnologies used for cleaning up urban and suburban polluted soils (i.e., brownfields) have shown some weakness in the excessive extent of the timeframe required for them to be effectively operating. This bottleneck is due to technical constraints, mainly related to both the nature of the pollutant itself (e.g., low bio-availability, high recalcitrance, etc.) and the plant (e.g., low pollution tolerance, low pollutant uptake rates, etc.). Despite the great efforts made in the last few decades to overcome these limitations, the technology is in many cases barely competitive compared with conventional remediation techniques. Here, we propose a new outlook on phytoremediation, where the main goal of decontaminating should be re-evaluated, considering additional ecosystem services (ESs) related to the establishment of a new vegetation cover on the site. The aim of this review is to raise awareness and stress the knowledge gap on the importance of ES associated with this technique, which can make phytoremediation a valuable tool to boost an actual green transition process in planning urban green spaces, thereby offering improved resilience to global climate change and a higher quality of life in cities. This review highlights that the reclamation of urban brownfields through phytoremediation may provide several regulating (i.e., urban hydrology, heat mitigation, noise reduction, biodiversity, and CO₂ sequestration), provisional (i.e., bioenergy and added-value chemicals), and cultural (i.e., aesthetic, social cohesion, and health) ESs. Although future research should specifically be addressed to better support these findings, acknowledging ES is crucial for an exhaustive evaluation of phytoremediation as a sustainable and resilient technology.

Climate justice in higher education: a proposed paradigm shift towards a transformative role for colleges and universities

Moving beyond technocratic approaches to climate action, climate justice articulates a paradigm shift in how organizations think about their response to the climate crisis. This paper makes a conceptual contribution by exploring the potential of this paradigm shift in higher education. Through a commitment to advancing transformative climate justice, colleges and universities around the world could realign and redefine their priorities in teaching, research, and community engagement to shape a more just, stable, and healthy future. As inequitable climate vulnerabilities increase, higher education has multiple emerging opportunities to resist, reverse, and repair climate injustices and related socioeconomic and health disparities. Rather than continuing to perpetuate the concentration of wealth and power by promoting climate isolationism's narrow focus on technological innovation and by prioritizing the financial success of alumni and the institution, colleges and universities have an opportunity to leverage their unique role as powerful anchor institutions to demonstrate climate justice innovations and catalyze social change toward a more equitable, renewable-based future. This paper explores how higher education can advance societal transformation toward climate justice, by teaching climate engagement, supporting impactful justice-centered research, embracing non-extractive hiring and purchasing practices, and integrating community-engaged climate justice innovations across campus operations. Two climate justice frameworks, Green New Deal-type policies and energy democracy, provide structure for reviewing a breadth of proposed transformational climate justice initiatives in higher education.

Turgor loss point and vulnerability to xylem embolism predict species-specific risk of drought-induced decline of urban trees

Increasing frequency and severity of drought events is posing risks to trees' health, including those planted in urban settlements. Drought-induced decline of urban trees negatively affects ecosystem services of urban green spaces and implies cost for maintenance and removal of plants. We aimed at identifying physiological traits that can explain and predict the species-specific vulnerability to climate change in urban habitats. We assessed the relationships between long-term risk of decline of different tree species in a medium-sized town and their key indicators of drought stress tolerance, i.e. turgor loss point (TLP) and vulnerability to xylem embolism (P₅₀ ). Starting from 2012, the study area experienced several summer seasons with positive anomalies of temperature and negative anomalies of precipitation. This trend was coupled with increasing percentages of urban trees showing signs of crown die-back and mortality. The species-specific risk of decline was higher for species with less negative TLP and P₅₀ values. The relationship between species-specific risk of climate change-induced decline of urban trees and key physiological indicators of drought tolerance confirms findings obtained in natural forests and highlights that TLP and P₅₀ are useful indicators for species selection for tree plantation in towns, to mitigate negative impacts of climate change.

Urban Heat Island Mitigation: GIS-Based Analysis for a Tropical City Singapore

To reduce the pace of climate change and achieve the goals set in Paris Agreement by 2030, Association of Southeast Asian Nations (ASEAN) countries have started to prioritize sustainability as one of their top agendas. Numerous studies have demonstrated that one of the most important issues that must be addressed to halt climate change is the urban heat island (UHI). Given the different mitigation strategies available, the focus of our study here is to assess the influence of green spaces and Green Mark commercial buildings on Singapore's temperature distribution using non-exhaustive factors related to energy consumption and efficiency. Additionally, this paper examines the effectiveness of green spaces and commercial buildings in reducing the rate of temperature change. This study uses ArcGIS software to map data, perform spatial analysis through cloud-based mapping, and produce visual representations with geographic information systems (GIS) to promote greater insight on the formulation of goals and policy making for strategic management. In comparison to non-commercial districts, our findings show that commercial districts have the lowest percentage of temperature change, an estimated 1.6 percent, due to a high concentration of green spaces and Green Mark commercial buildings. Our research also helps to close the research gaps in determining the efficacy of Green Mark commercial buildings, skyrise greeneries, gardens, and national parks. It also helps to minimize the bottleneck of expensive building costs and environmental damage that would have occurred from a design flaw found too late in the urban planning and construction process.

Mortality Burden of Heatwaves in Sydney, Australia Is Exacerbated by the Urban Heat Island and Climate Change: Can Tree Cover Help Mitigate the Health Impacts?

Heatwaves are associated with increased mortality and are exacerbated by the urban heat island (UHI) effect. Thus, to inform climate change mitigation and adaptation, we quantified the mortality burden of historical heatwave days in Sydney, Australia, assessed the contribution of the UHI effect and used climate change projection data to estimate future health impacts. We also assessed the potential for tree cover to mitigate against the UHI effect. Mortality (2006–2018) records were linked with census population data, weather observations (1997–2016) and climate change projections to 2100. Heatwave-attributable excess deaths were calculated based on risk estimates from a published heatwave study of Sydney. High resolution satellite observations of UHI air temperature excesses and green cover were used to determine associated effects on heat-related mortality. These data show that >90% of heatwave days would not breach heatwave thresholds in Sydney if there were no UHI effect and that numbers of heatwave days could increase fourfold under the most extreme climate change scenario. We found that tree canopy reduces urban heat, and that widespread tree planting could offset the increases in heat-attributable deaths as climate warming progresses.

Estimating the Evaporative Cooling Effect of Irrigation within and above Soybean Canopy

Vegetation with an adequate supply of water might contribute to cooling the land surface around it through the latent heat flux of transpiration. This study investigates the potential estimation of evaporative cooling at plot scale, using soybean as example. Some of the plants’ physiological parameters were monitored and sampled at weekly intervals. A physics-based model was then applied to estimate the irrigation-induced cooling effect within and above the canopy during the middle and late season of the soybean growth period. We then examined the results of the temperature changes at a temporal resolution of ten minutes between every two irrigation rounds. During the middle and late season of growth, the cooling effects caused by evapotranspiration within and above the canopy were, on average, 4.4 K and 2.9 K, respectively. We used quality indicators such as R-squared (R2) and mean absolute error (MAE) to evaluate the performance of the model simulation. The performance of the model in this study was better above the canopy (R2 = 0.98, MAE = 0.3 K) than below (R2 = 0.87, MAE = 0.9 K) due to the predefined thermodynamic condition used to estimate evaporative cooling. Moreover, the study revealed that canopy cooling contributes to mitigating heat stress conditions during the middle and late seasons of crop growth.

Urban environments have species-specific associations with invasive insect herbivores

Urban forests are critically important for providing ecosystem services to rapidly expanding urban populations, but their health is threatened by invasive insect herbivores. To protect urban forests against invasive insects and support future delivery of ecosystem services, we must first understand the factors that affect insect density across urban landscapes. This study explores how a variety of environmental factors that vary across urban habitats influence density of invasive insects. Specifically, we evaluate how vegetational complexity, distance to buildings, impervious surface, canopy temperature, host availability and density of co-occurring herbivores impact three invasive pests of elm trees: the elm leaf beetle (Xanthogaleruca luteola), the elm flea weevil (Orchestes steppensis) and the elm leafminer (Fenusa ulmi). Insect responses to these factors were species-specific, and all environmental factors were associated with density of at least one pest species except for distance to buildings. Elm leafminer density decreased with higher temperatures and was influenced by an interaction between vegetational complexity and impervious surface. Elm flea weevil density increased with greater host availability, and elm leaf beetle density increased with higher temperatures. Both elm leaf beetle and elm flea weevil density decreased with greater leafminer density, suggesting that insect density is mediated by species interactions. These findings can be used to inform urban pest management and tree care efforts, making urban forests more resilient in an era when globalization and climate change make them particularly vulnerable to attack.

The association of fractional cover, foliage projective cover and biodiversity with birthweight

INTRODUCTION

Environmental exposures can contribute both benefits and risks to human health. Maternal exposure to green space has been associated with improvements in birthweight, among other birth outcomes. Newer measures of green space have been developed, which allows for an exploration of the effect of different ground covers (green, dry and bare earth), as well as measures of biodiversity. This study explores the association of these novel green space measures with birthweight in a large birth cohort in Queensland, Australia.

METHODS

Birthweight was acquired from the routine health records. Records were allocated green space values for fractional cover, biodiversity and foliage projective cover. Directed acyclic graphs were developed to guide variable selection. Mixed-effects linear regression and generalised linear mixed-effects models were developed, with random intercepts for maternal residential locality and year of birth. Results are presented as standardised beta coefficients or odds ratios, with 95% confidence intervals.

RESULTS

An IQR increase of green cover (29.6 g, 95% CI 13.8-45.5) and foliage projective cover (26.0 g, 95% CI 10.8-41.3) are associated with birthweight in urban areas. An IQR increase in dry cover -34.4 g, 95% CI -60.4 to -8.4) and bare earth (-17.7 g, 95% CI -32.8 to -2.6) are associated with lower birthweight. Mothers living in rural areas had similar results, with an IQR increase in green cover (17.8 g, 95% CI 2.9-32.7) associated with higher birthweight, and bare earth (-27.7 g, 95% CI -45.7 to -9.7) was associated with lower birthweight. The biodiversity measure used in this study was not associated with any birthweight outcomes.

CONCLUSION

This study finds that the types of ground cover within the maternal residential locality are associated with small, but significant, changes in estimated birthweight, and these effects are not limited to urban areas.

Biophilia beyond the Building: Applying the Tools of Urban Biodiversity Planning to Create Biophilic Cities

In response to the widely recognized negative impacts of urbanization on biodiversity, many cities are reimagining urban design to provide better biodiversity support. Some cities have developed urban biodiversity plans, primarily focused on improving biodiversity support and ecosystem function within the built environment through habitat restoration and other types of urban greening projects. The biophilic cities movement seeks to reframe nature as essential infrastructure for cities, seamlessly integrating city and nature to provide abundant, accessible nature for all residents and corresponding health and well-being outcomes. Urban biodiversity planning and biophilic cities have significant synergies in their goals and the means necessary to achieve them. In this paper, we identify three key ways by which the urban biodiversity planning process can support biophilic cities objectives: engaging the local community; identifying science-based, quantitative goals; and setting priorities for action. Urban biodiversity planning provides evidence-based guidance, tools, and techniques needed to design locally appropriate, pragmatic habitat enhancements that support biodiversity, ecological health, and human health and well-being. Developing these multi-functional, multi-benefit strategies that increase the abundance of biodiverse nature in cities has the potential at the same time to deepen and enrich our biophilic experience in daily life.

Multi-Temporal Land Surface Temperature and Vegetation Greenness in Urban Green Spaces of Puebla, Mexico

The urban heat island (UHI) effect is a global problem that is likely to grow as a result of urban population expansion. Multiple studies conclude that green spaces and waterbodies can reduce urban heat islands. However, previous studies often treat urban green spaces (UGSs) as static or limit the number of green spaces investigated within a city. Cognizant of these shortcomings, Landsat derived vegetation and land surface temperature (LST) metrics for 80 urban green spaces in Puebla, Mexico, over a 34-year (1986–2019) and a 20-year (2000–2019) period were studied. To create a photo library, 73 of these green spaces were visited and the available land cover types were recorded. Green spaces with Indian laurel were found to be much greener and vegetation index values remained relatively stable compared to green spaces with mixed vegetation cover. Similarly, green spaces with large waterbodies were cooler than those without water. These results show that larger green spaces were significantly cooler (p < 0.01) and that size can explain almost 30% of temperature variability. Furthermore, green spaces with higher vegetation index values were significantly cooler (p < 0.01), and the relationship between greenness and temperature strengthened over time.

Urban soils research: SUITMA 10

Research on Soils in Urban, Industrial, Traffic, Mining and Military Areas (SUITMA) has been presented at biennial SUITMA conferences held in cities around the world. Soils from these areas often present environmental, ecological, and health risks and can limit ecological functions and ecosystem services. However, as with all soils, they are an integral part of the local ecosystem. In urban areas in particular, soil is a critical resource and can play a key role in the long-term sustainability and resiliency of cities. This special section contains five papers from the SUITMA 10 conference held in Seoul, South Korea, in 2019. They cover diverse topics that include urban soil properties, risk from contaminated soils, biological indicators for ecological functions, air deposition in urban gardens, and international summer field school opportunities. This section highlights research on anthropogenic soils conducted by the SUITMA community to promote better understanding and management of these soils.

Green Infrastructure as an Urban Heat Island Mitigation Strategy—A Review

Research on urban heat mitigation has been growing in recent years with many of the studies focusing on green infrastructure (GI) as a strategy to mitigate the adverse effects of an urban heat island (UHI). This paper aims at presenting a review of the range of findings from GI research for urban heat mitigation through a review of scientific articles published during the years 2009–2020. This research includes a review of the different types of GI and its contribution for urban heat mitigation and human thermal comfort. In addition to analysing different mitigation strategies, numerical simulation tools that are commonly used are also reviewed. It is seen that ENVI-met is one of the modelling tools that is considered as a reliable to simulate different mitigation strategies and hence has been widely used in the recent past. Considering its popularity in urban microclimate studies, this article also provides a review of ENVI-met simulation results that were reported in the reviewed papers. It was observed that the majority of the research was conducted on a limited spatial scale and focused on temperature and human thermal comfort.

Impacts of Exotic Pasture Establishment on Dung Beetle Assemblages (Coleoptera: Scarabaeidae: Scarabaeinae) in the Brazilian Cerrado

The Brazilian Cerrado is the second largest Neotropical biome and an important hotspot of biodiversity. However, land use change in this ecosystem is producing landscapes with modified natural environments and anthropogenic environments, such as exotic pastures. In this study, we evaluated how conversion of native Cerrado vegetation to exotic pastures affects the dung beetle assemblages (Coleoptera: Scarabaeidae: Scarabaeinae). We sampled dung beetles in four areas of Cerrado (sensu stricto) and in four areas of exotic pastures (Urochloa spp.) in Aquidauana, Mato Grosso do Sul, Brazil. In all, 7,544 individuals from 43 species of dung beetles were collected, and 19 species were found in both the Cerrado and exotic pastures. The abundance and species richness of dung beetles were higher in Cerrado remnants. Species composition differed between Cerrado and exotic pastures, where 11 species were classified as specialists of Cerrado, 10 species were considered specialists of exotic pastures, and 6 species were habitat generalists. Roller beetles were most negatively affected by exotic pasture establishment. We demonstrated that exotic pasture establishment has a negative impact on dung beetle assemblages in Brazilian Cerrado. The decline in abundance and richness of roller beetles has important implications for the understanding of ecosystem functioning because it can reduce the ecological functions performed by dung beetle assemblages in exotic pastures. Finally, the high number of dung beetle species shared between Cerrado and exotic pastures suggests that the Cerrado remnants is a fundamental requirement for the conservation of biodiversity of dung beetles in exotic pastures in the Brazilian Cerrado.

Cooling effect and control factors of common shrubs on the urban heat island effect in a southern city in China

Because the heat island effect can make cities warmer than their surroundings, it can make urban dwellers uncomfortable and even affect their health, which is particularly pronounced in developed cities in southern China. To reduce the heat island effect and improve the environment, various types of vegetation have been planted in the urban green belt. Though previous studies have been conducted on the beauty, air purification functions and cooling effect of vegetation, little is concentrated on the different cooling effects and control factors of various common shrubs on the heat island effect in cities. In this study, five of the most regionally common shrubs were selected to study the cooling effect in Guangzhou, southern China. The maximum surface temperatures of five shrubs and pavement were compared using infrared temperature sensors from April 1st 2019 to October 31st 2019. Results show that (1) All five shrubs showed noticeable seasonal variation, and the average surface temperatures of the five shrubs were between 38.0 and 42.2 °C during May–August and 30.7–34.1 °C during the other seasons (April, September and October);. (2) Murraya exotica L. exhibited the best cooling effect on the maximum surface temperature. Its value was 44.7 °C, and the absolute difference values of Murraya exotica L. (10.3 ± 1.7 °C) were higher than any other shrub during the study period; (3) Both the LAI (R² = 0.57, p < 0.01) and plant height (R² = 0.13, p < 0.01) are control factors of the cooling effect on vegetation surface temperature for the five shrubs. This study revealed the differences in the cooling effect and influencing factors of five regionally common shrubs on the heat island effect. Research on the functional characteristics of plants and plant selection in urban green belts has both theoretical and practical significance.

Realised rather than fundamental thermal niches predict site occupancy: Implications for climate change forecasting

Thermal performance traits are regularly used to make forecasts of the responses of ectotherms to anthropogenic environmental change, but such forecasts do not always differentiate between fundamental and realised thermal niches. Here we determine the relative extents to which variation in the fundamental and realised thermal niches accounts for current variation in species abundance and occupancy and assess the effects of niche-choice on future-climate response estimations. We investigated microclimate and macroclimate temperatures alongside abundance, occupancy, critical thermal limits and foraging activity of 52 ant species (accounting for >95% individuals collected) from a regional assemblage from across the Western Cape Province, South Africa, between 2003 and 2014. Capability of a species to occupy sites experiencing the most extreme temperatures, coupled with breadth of realised niche, explained most deviance in occupancy (up to 75%), while foraging temperature range and body mass explained up to 50.5% of observed variation in mean species abundance. When realised niches are used to forecast responses to climate change, large positive and negative effects among species are predicted under future conditions, in contrast to the forecasts of minimal impacts on all species that are indicated by fundamental niche predictions.

On the Efficiency of Using Transpiration Cooling to Mitigate Urban Heat

Trees are considered to be effective for the mitigation of urban overheating, and the cooling capacity of trees mainly comes from two mechanisms: transpiration and shading. This study explores the transpiration cooling of large trees in urban environments where the sea breeze dominates the climate. In the experiment, sap flow sensors were used to measure the transpiration rate of two large trees located in Sydney over one year. Also, the temperature difference between the inside and outside of the canopy, as well as the vertical temperature distribution below the canopy, were measured during summer. In this experiment, the temperature under the canopies decreased by about 0.5 degrees from a 0.5 m height to a 3.5 m height, and the maximum temperature difference between the inside and outside of the canopy was about 2 degrees. After applying a principal component analysis of multiple variables, we found that when a strong sea breeze is the primary cooling mechanism, the sap flow still makes a considerable contribution to cooling. Further, the sea breeze and the transpiration cooling of trees are complementary. In conclusion, the characteristics of synoptic conditions must be fully considered when planting trees for mitigation purposes. Since the patterns of sea breeze and sap often do not coincide, the transpiration cooling of trees is still effective when the area is dominated by sea breeze.

How Cool Are Allotment Gardens? A Case Study of Nocturnal Air Temperature Differences in Berlin, Germany

Urban green infrastructures have been extensively studied for their ability to mitigate the urban heat island (UHI) effect. However, allotment gardens (AGs)—a prominent type of urban green infrastructure within many European cities—have not yet been comprehensively investigated concerning their microclimates. In this study, nocturnal air temperatures ( T N ) in 13 AG complexes (AGCs) were measured during the summer of 2018 in Berlin, Germany. These were compared to measurements in densely built-up urban areas (URB), two large inner-city parks and rural areas (RUR). On average, the assessed AGCs were 2.7 K cooler at night than URB. Most of the investigated AGCs (11/13) displayed a larger mean T N difference to URB ( Δ T N   A G C   ¯ ) than the examined urban parks. RUR showed the largest differences to URB ( Δ T N   R U R ¯ ), indicating a UHI effect. Furthermore, the influence of land surface characteristics of the AGCs on Δ T N   A G C ¯ was analyzed. Δ T N   A G C ¯ decreased significantly as the floor space index around AGCs increased. The analysis of the shape complexity also produced a significant positive correlation with Δ T N   A G C ¯ . In contrast, size and distance to the city center of an AGC decreased significantly with increasing Δ T N   A G C ¯ . This study provides first insights into the microclimate of AGs and influencing variables concerning T N .

A New Individual Tree Crown Delineation Method for High Resolution Multispectral Imagery

In current individual tree crown (ITC) delineation methods for high-resolution multispectral imagery, either a spectral band or a brightness component of the multispectral image is employed in delineation with reference to edges or shapes of crowns, whereas spectra of tree crowns are seldom taken into account. Such methods normally perform well in coniferous forests with obvious between-crown shadows, but fail in dense deciduous or mixed forests, in which tree crowns are close to each other, between-crown shadows and boundaries are unobvious, whereas adjacent tree crowns may be of distinguishable spectra. In order to effectively delineate crowns in dense deciduous or mixed forests, a new ITC delineation method using both brightness and spectra of the image is proposed in this study. In this method, a morphological gradient map of the image is first generated, treetops of multi-scale crowns are extracted from the gradient map and refined regarding the spectral differences between neighboring crowns, the gradient map is segmented using a watershed approach with treetops as markers, and the resulting segmentation map is refined to yield a crown map. Evaluated on images of a rainforest and a deciduous forest, the proposed method more accurately delineated adjacent broad-leaved tree crowns with similar brightness but different spectra than the other two typical ITC delineation algorithms, achieving a delineation accuracy of up to 76% in the rainforest and 63% in the deciduous forest.

Greening Blocks: A Conceptual Typology of Practical Design Interventions to Integrate Health and Climate Resilience Co-Benefits

It is increasingly evident that exposure to green landscape elements benefits human health. Urban green space in cities is also recognized as a crucial adaptation response to changes in climate and its subsequent effects. The exploration of conceptual and practical intersections between human health, green spaces, and climate action is needed. Evidence-based guidance is needed for stakeholders, practitioners, designers, and citizens in order to assess and manage urban green spaces that maximize co-benefits for both human health and climate resilience. This paper proposes interventions that provide strategic green space enhancement at the neighborhood and block scale. We propose eight tangible green space interventions and associated metrics to integrate climate resilience and population health co-benefits into urban green space design and planning: View from within, Plant entrances, Bring nature nearby, Retain the mature, Generate diversity, Create refuge, Connect experiences, and Optimize green infrastructure. These interventions represent a hierarchy of functional design concepts that respond to experiential qualities and physical/psychological dimensions of health, and which enhance resilience at a range of social scales from the individual to the neighborhood. The interventions also reveal additional research needs in green space design, particularly in neighborhood-level contexts.

Process based simulation of tree growth and ecosystem services of urban trees under present and future climate conditions

Global processes of urban growth lead to severe environmental impacts such as temperature increase with an intensification of the urban heat island effect, and hydrological changes with far reaching consequences for plant growth and human health and well-being. Urban trees can help to mitigate the negative effects of climate change by providing ecosystem services such as carbon storage, shading, cooling by transpiration or reduction of rainwater runoff. The extent of each ecosystem service is closely linked with the tree species as well as with a tree's age, size, structure and vitality. To evaluate the ecosystem services of urban trees, the process-based growth model CityTree was developed which is able to estimate not only tree growth but also the species-specific ecosystem services including carbon storage, transpiration and runoff, shading, and cooling by transpiration. The model was parametrized for the species small-leaved lime (Tilia cordata), robinia (Robinia pseudoacacia), plane (Platanus×acerifolia) and horse chestnut (Aesculus hippocastanum). The model validation for tree growth (stem diameter increment, coefficient of correlation=0.76) as well as for the water balance (transpiration, coefficient of correlation=0.92) seems plausible and realistic. Tree growth and ecosystem services were simulated and analyzed for Central European cities both under current climate conditions and for the future climate scenarios. The simulations revealed that urban trees can significantly improve the urban climate and mitigate climate change effects. The quantity of the improvements depends on tree species and tree size as well as on the specific site conditions. Such simulation scenarios can be a proper basis for planning options to mitigate urban climate changes in individual cities.

Land pavement depresses photosynthesis in urban trees especially under drought stress

Investigations into the photosynthetic response of urban trees on paved land under drought stress would help to improve the management of trees under rapid urbanization and climate change. An experiment was designed to grow two common greening tree saplings, ash (Fraxinus chinensis Roxb.) and ginkgo (Ginkgo biloba L.), in environments of both land pavement and drought. The results showed that (1) land pavement increased surface and air temperatures and decreased air humidity as well as net photosynthetic rate (P_n) and photosynthetic capacity (A_max) of ginkgo significantly; (2) drought significantly decreased P_n, A_max and maximum net photosynthetic rate (P_nmax) as well as other photosynthetic parameters of both ash and ginkgo; (3) the negative effects of the combination of land pavement and drought on photosynthetic parameters were more significant than the effects of drought treatment for both ash and ginkgo. This implies that urban trees, especially those growing on land pavements, will confront harsher environments and a greater decline of photosynthesis under the severe and more frequent droughts predicted in the future. Overall, ash showed more tolerance to land pavement and drought than ginkgo, indicating that the selection of tolerant tree species is important for urban planting.

The nexus between climate change, ecosystem services and human health: Towards a conceptual framework

This paper addresses the impact that changes in natural ecosystems can have on health and wellbeing focusing on the potential co-benefits that green spaces could provide when introduced as climate change adaptation measures. Ignoring such benefits could lead to sub-optimal planning and decision-making. A conceptual framework, building on the ecosystem-enriched Driver, Pressure, State, Exposure, Effect, Action model (eDPSEEA), is presented to aid in clarifying the relational structure between green spaces and human health, taking climate change as the key driver. The study has the double intention of (i) summarising the literature with a special emphasis on the ecosystem and health perspectives, as well as the main theories behind these impacts, and (ii) modelling these findings into a framework that allows for multidisciplinary approaches to the underlying relations between human health and green spaces. The paper shows that while the literature based on the ecosystem perspective presents a well-documented association between climate, health and green spaces, the literature using a health-based perspective presents mixed evidence in some cases. The role of contextual factors and the exposure mechanism are rarely addressed. The proposed framework could serve as a multidisciplinary knowledge platform for multi-perspecitve analysis and discussion among experts and stakeholders, as well as to support the operationalization of quantitative assessment and modelling exercises.

Vertical air temperature gradients under the shade of two contrasting urban tree species during different types of summer days

Moderation of thermal energy balance through the canopies of urban trees is well known. However, a more functional and quantitative view of the heterogeneous urban environment and their influence on the below-canopy vertical air temperature gradients is largely missing. Throughout the summer 2016 we continuously measured air temperature at three different heights (at 1.5, 3 and 4.5m from the ground) under the canopies of two common but contrasting street tree species in respect of eco-physiology and morphology in Munich, Germany: Robinia pseudoacacia L. (ring porous) and Tilia cordata Mill. (diffuse porous). Along with air and surface temperature we also measured meteorological and edaphic variables and categorized summer time as cool, mild, summer and hot days. Global radiation, vapour pressure deficit and soil temperature increased as the days got warmer but precipitation, soil moisture and wind speed showed the reversed pattern. Overall, T. cordata trees with higher leaf area index and sap-wood area provided three times more transpiration than R. pseudoacacia. On an average air temperature gradient of outside to inside canopy dropped from 1.8°C to 1.3°C for T. cordata but from 1.5°C to only 0.5°C for R. pseudoacacia as the days got warmer. Vertical decline of air cooling effect was around 1°C from canopy to the near-ground (1.5m). Lower soil moisture but higher soil temperature suggested that cool air from the canopy mixed with a higher amount of sensible heat flux under the canopies of T. cordata compared to the R. pseudoacacia as the days got warmer. The study indicated a threshold for extreme hot days when grass surface evapotranspirational cooling will not be as effective and act like built surfaces rather deep shading from tree canopies will be important.

Urban River Reserve Potentials as Passive Cooling Strategies

In Malaysia, urban riparian refers to river reserve that reflects green space. As surviving greenery space amidst concrete jungle, urban riparian is essential for safe-keeping the river health, the surrounding environment, and the well-being of urbanites. The existing developments found by the Malaysian riversides are already in place prior to river reserves establishment, thus constricting expansion and synchronisation due to its guidelines applied in isolation within several related agencies. Prior studies have highlighted the potential of riparian vegetation as a viable method that lowers the temperature within urban space. Hence, this paper probes into the potential of river reserve as a passive cooling strategy by determining the vegetation technical requirements from the light of urban river physical planning and design guidelines in Malaysia. Thus, this study outlines the possibility of integration by comparing vegetation requirements for river buffer with vegetation function and ability in altering radiation, as well as heat transfer, through physical attributes. By focusing on vegetation physical structure, the riparian area can attain multiple functions and benefits. Thus, this finding serves as a basis for integration of passive cooling strategies with vegetation requirements for urban river reserve, and for further studies that investigate other essential physical attributes.

Is All Urban Green Space the Same? A Comparison of the Health Benefits of Trees and Grass in New York City

Living near vegetation, often called “green space” or “greenness”, has been associated with numerous health benefits. We hypothesized that the two key components of urban vegetation, trees and grass, may differentially affect health. We estimated the association between near-residence trees, grass, and total vegetation (from the 2010 High Resolution Land Cover dataset for New York City (NYC)) with self-reported health from a survey of NYC adults (n = 1281). We found higher reporting of “very good” or “excellent” health for respondents with the highest, compared to the lowest, quartiles of tree (RR = 1.23, 95% CI = 1.06–1.44) but not grass density (relative risk (RR) = 1.00, 95% CI = 0.86–1.17) within 1000 m buffers, adjusting for pertinent confounders. Significant positive associations between trees and self-reported health remained after adjustment for grass, whereas associations with grass remained non-significant. Adjustment for air pollutants increased beneficial associations between trees and self-reported health; adjustment for parks only partially attenuated these effects. Results were null or negative using a 300 m buffer. Findings imply that higher exposure to vegetation, particularly trees outside of parks, may be associated with better health. If replicated, this may suggest that urban street tree planting may improve population health.