Urban agglomeration has become the most salient feature of global urbanization in recent decades, while spatiotemporal patterns and evolution remain poorly understood in urban agglomerations, which ...limit the decision-makers to make more informed decisions to improve the regional environment. Here we selected one of the most rapidly urbanized regions in the world – Pearl River Delta Metropolitan Region (PRDR), located in southern China, as the case. Landsat images spanning from 1995 to 2015 were used to retrieve land surface temperature (LST). Four types of regional heat island (RHI) degree were defined for further analysis. Then multi-scale spatiotemporal patterns and characteristics of RHI were identified with the help of cloud-based computing, spatial and landscape analysis. We found that (1) traditional urban heat island (UHI) appears as an RHI on an urban agglomeration scale. In PRDR, we found RHI expended with increasing connectivity, especially in the estuary areas where isolated UHI gradually merged during the rapid urbanization. (2) The contribution of main cities in PRDR to RHI and the evolutionary trends and pattern, which is changed from a west-east to a southwest-northeast gradient, have been revealed. (3) Considering the scale effect and different RHI categories, we revealed that during the urbanization, the aggregation of the RHI is significant on a larger-scale, and the area of 4 °C ≤ Relative LST ≤ 8 °C is the stable and high-risk area, which provide scientific bases for the governance of the thermal environment on the regional scale. (4) The study also indicates the cooling effect of forests and water is better than that of grassland, while the cooling effect of grassland is uncertain. The methods and results of this study not only have implications on environmental planning and management in the PRDR but also provide useful insights into the thermal environment research and practice in other urban agglomerations.
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•Spatiotemporal patterns and detailed characteristics of RHIs in PRDR was investigated.•Effects and patterns of rapid urbanization on emerging RHIs was revealed.•Hotspots and additional possibilities of heat risk exposure in the PRDR was proposed.•The urgency of thermal environment governance at the regional scale has been proved.•Differences in cooling effect between water, tree and grassland were also discovered.
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•The cooling effect of urban blue-green space and threshold-size-based studies are reviewed.•The controversies and uncertainties on the cooling effect of urban blue-green space are ...revealed.•The basic framework and perspective of the urban cooling effect studies are proposed.•The new technology and method for furthering urban cooling effect studies are suggested.•The implications of the threshold-size of blue-green space for actionable climate adaption planning are discussed.
The cooling effect of blue-green space has been recognized as a promising approach to mitigate the urban heat island (UHI), while the quantitative role (threshold-size for cooling) is still uncertain. This paper aims to present the latest progress and controversies on the studies of the cooling effects of waterbodies, greenspaces, and parks. In order to do this research, international search engines were employed to systematically search peer-reviewed articles, including the cooling effect of blue-green space and threshold-size-based UHI mitigation studies. After that, the inductive analysis is used to analyze the relevant literature. We found that previous studies concentrated on the correlations between different landscape types, temperature variations and the quantification of cooling intensity, etc. However, threshold-size-based research has received less attention, which limits the ability to make specific recommendations for actionable planning and management – usingthe smallest blue-green space for the best cooling effect. The review also revealed the controversies over the effects of blue-green space size, shape, landscape composition and configuration on cooling effect. Besides, we pointed out that the uncertainties (i.e., the optimal proportion of blue-green space in a park) and the reasons of controversial results of the cooling effect need to be further investigated. We also suggested that more attention should be paid to quantify the contributions of local background climate and landscape characteristics to the cooling effect (threshold-size) of blue-green space. This review would give us a deeper understanding of the field and provide insights into actionable climate adaption planning.
•Ecosystem service benefits and losses in the Yangtze River Delta urban agglomeration are calculated.•The patterns and the main providers of ecosystem services within different landscape types are ...revealed.•Multi-scale analyses are used to divide different functional zone areas.•Three functional zones within the Yangtze River Delta urban agglomeration are proposed.
The comprehensive management of ecosystem service benefits and losses provided by landscapes under land-use reorganization is essential for optimizing and regulating landscape patterns and ecological conservation under rapid urbanization. Of the many studies focusing on the quantification and visualization of ecosystem services, few have explored the visualization characteristics of the different scales related to ecosystem services and losses. In this study, we selected one of the most important urban agglomerations in China—the Yangtze River Delta (YRD)—as a case for the analysis of ecosystem service benefits (which include environmental purification, climate and air regulation, and tourism and leisure) and losses (pollen allergies, air pollution, and the heat island effect) and the spatial patterns of both at multiple scales (grid divisions, administrative districts, and functional areas). We found that the value of ecosystem service losses in the YRD, with a net value of approximately −$42.02 × 106, was slightly higher than the value of ecosystem service benefits. The patterns of ecosystem service benefits were consistent with urbanization processes and patterns, with the natural landscape always serving as the main provider of ecosystem service benefits while the spatial pattern of the urbanized landscape determined the ecosystem service losses. Based on K-means clustering using randomly selected objects as an initial cluster center, we divided the YRD into different functional areas (optimized-, key-, and restricted-development zones) within the grid to create divisions with consistent biophysical properties, thereby avoiding the impact of urban administrative boundaries on the results. To facilitate closing the gap between positive and negative ecosystem outcomes in a politically feasible manner, we also identified functional areas in terms of ecosystem service bundles at the administrative district scale. This study obtains quantitative knowledge of functional areas based on ecosystem services benefits and losses, and helps guide sustainable urban agglomeration planning and development.
Considerable specific cross-sectional and review studies have linked exposure to green spaces to improving public health, but there is no bibliometric review attempting to systemically and ...retrospectively analyze these existing articles. Here we aim to uncover global research status, trends, and future prospects in green spaces and health (G-H) research then propose a framework for the underlying mechanisms and pathways that link green space to public health. We obtained 18 961 G-H research publications from the core Web of Science collection from 1901 to 2019, analyzing the characteristics of publication outputs, key scientific disciplines, and differences in performance between countries and institutions. Besides, content analysis was conducted to analyze the keywords, including keyword co-occurrence analysis and keyword clustering analysis. We found: (1) a steady quantitative increase in publications, active journals, and involved countries and institutions since the 1990s; (2) a signi cant increase and changes in G-H related interdisciplinary categories, with environment-related disciplines becoming the mainstream; (3) research focus and trends that were identified based on the analysis of high-frequency co-occurring keywords; (4) three main knowledge domains, namely, green spaces and physical health, mental health, and ecosystem health, that were identified and visualized based on keyword clustering analysis; (5) a framework of underlying mechanisms and pathways linking green space to public health that is proposed based on visualization of the three main knowledge domains. We suggest that the main challenge of G-H research is to further clarify in-depth the underlying mechanisms and pathways from multiple perspectives, including multiple nations, disciplines, and study designs. The lack of co-occurring keywords and clustering information related to social well-being suggests that research related to 'social health' is lacking. Based on a clear understanding of the quantity, quality, and characteristics of green space for public health, a health-based environmental plan should be proposed in the future.
•The benefits of existing natural forest ecosystem on climate mitigation are demonstrated.•RTE is significantly influenced by the specific land conversion processes are found.•RTE dynamic during the ...urbanization might conform to Environmental Kuznets Curve are suggested.•RHI can better describe heat island effect in urban agglomeration context are proposed.
Urbanization has significantly transformed natural surfaces into impervious surfaces, which has subsequently disturbed the balance of the global surface thermal energy. However, key landscape dynamic transfer processes that can affect land surface temperature (LST) and regional thermal environment (RTE) remain poorly understood, especially in the context of urban agglomerations. Hence we selected one of the world's most rapidly urbanized regions – the Pearl-River-Delta Metropolitan Region (PRDR) located in southern China as the case. With the help of Google Cloud Computing, Markov model, and spatial analyses, we have further quantified the strong contributions of urbanization and urban agglomeration development to RTE dynamics and evolution. Specifically, we revealed (1) the cooling effects of ecological land loss and gain are significantly different, which provides evidence that the existing natural ecosystems (especially forests) are valuable for climatic adaptation because newly constructed ecological land does not provide the same cooling effect. (2) We found that the RTE is not only influenced by land cover patterns and process but also significantly dominated by the specific land conversion processes. (3) From 1995 to 2015 in the PRDR, built-up land increased significantly, while the ecological land was significantly reduced, and the isolated urban heat islands were gradually connected and interacted with each other, forming the regional heat island. (4) We also proposed that the relationship between urbanization rate and temperature (RLST) may conform to the Environmental Kuznets Curve. This study enhances the understanding of RTE dynamics and evolution in urban agglomeration and provides important insights into existing natural ecosystem protection and climate adaptation planning.
Utilization of urban green vegetation (UGV) has been recognized as a promising option to mitigate urban heat island (UHI) effect. While we still lack understanding of the contributions of local ...background climate to the cooling effect of UGV. Here we proposed and employed a cooling effect framework and selected eight typical cities located in Temperate Monsoon Climate (TMC) and Mediterranean Climate (MC) demonstrate that local climate condition largely affects the cooling effect of UGV. Specifically, we found increasing (artificial) rainfall and irrigation contribute to improving the cooling intensity of grassland in both climates, particularly in the hot-dry environment. The cities with high relative humidity would restrict the cooling effect of UGV. Increasing wind speed would significantly enhance the tree-covered while weakening the grass-covered UGVs' cooling effect in MC cities. We also identified that, in order to achieve the most effective cooling with the smallest sized tree-covered UGV, the area of trees in both climate zones' cities should generally be planned around 0.5 ha. The method and results enhance understanding of the cooling effect of UGVs on larger (climate) scales and provide important insights for UGV planning and management.
Rapid urbanization has caused significant land cover change (LCC) as well as changes in the land surface temperature (LST). However, the crucial land dynamic process, which could significantly ...contribute to the increase in LST and aggravation of the urban heat island (UHI) effect, remains poorly understood. Additionally, a strategy to optimize the most significant decreased land cover type in order to maximize the cooling effect is still lacking. Therefore, in this study, we selected the rapidly urbanizing and ‘hottest’ city in China, Fuzhou, as a case study. Two algorithms were selected to compare and obtain reliable LST data. A land use transfer matrix was used to detect critical contributions leading to the LST variations. The concept of cooling efficiency (CE) and the threshold value of efficiency (TVoE) are also proposed, defined, and calculated. The results show that LST values increased with increasing proportion of built-up land and sharply decreasing proportion of green space. Areas where LST differences exceed 4°C cover 93% of the areas where green spaces decreased. Additionally, the LST variation is not only associated with the dominant land cover types but is also affected by the land cover transfer pattern and dynamics. Finally, we have calculated the TVoE of green space in Fuzhou city to be 4.55±0.5ha. This finding implies that when Fuzhou municipality implements urban/landscape planning, a green space area of 4.55±0.5ha is the most efficient to reduce the heat effect. This study extends the current understanding of LCC dynamics and LST variation. The concepts of the CE and TVoE are meaningful for landscape planning practice and can be used in other cases.
Contexts
Urban green infrastructure (UGI) has been recognized as a promising approach to mitigating urban heat island (UHI); however, most of the previous studies are case-based and explore the ...effects of the existent landscape and its spatial configuration on UHI mitigation rather than modeling an optimized spatial pattern.
Objectives
We aimed to transcend the existing research logic (from case studies to obtain the patterns of the cooling effect of UGI, then propose implications for UHI mitigation) and established a hypothetical idealized urban thermal security pattern model (TSP
urban
).
Methods
Based on two basic concepts deduced from the physical property of UGI—(threshold) size and cooling distance, as well as the simplifying assumptions we defined. Then, three proposed conceptual UGI types (ecological, efficient, and elementary—3E) and subtypes were used to frame the model.
Results
We deduced that the idealized TSP
urban
model conforms to a hierarchical hexagonal structure in theory and it can be calculated and applied, although it generally cannot be seen in the real world.
Conclusions
The idealized TSP
urban
model can help us better-understanding UGI cooling effects when considering climate adaption planning and decision-making; it also serves as a novel pathway to study the cooling effects of UGI and mitigate the UHI effect.
The process of urban renewal extensively changes residents' physical and social environments and, at the same time, reconstructs their social networks. Although there is a growing interest in ...analyzing the determinants of social networks, extant research neither accounts for the change in social networks after urban renewal nor considers the various residential groups affected by urban renewal. This work of research aims to examine the impact of urban renewal on social networks within neighborhoods based on three affected residential groups (in-site stayers, nearby stayers, and relocated residents) using data collected from six renewal areas in Chongqing, China. The results show that physical and social environmental changes significantly influence social networks during urban renewal. Socio-demographic factors such as age and education are associated with social network changes. The three affected residential groups identified significant differences in social networks after urban renewal. Nearby stayers experienced the largest increase in their network, while relocated residents experienced the most significant decrease. Social network changes for the same affected residential group also vary based on socioeconomic factors and perceptions of the residential environment. Targeted policy implications are provided for the specific affected residential groups.
•Urban renewal changes social networks under the influence of sociodemographics, and neighborhood social and physical attributes.•Heterogeneity in social networks is shown after urban renewal among three residential groups.•Each residential group experienced different social network dynamics after urban renewal depending on socioeconomic status and perceptions of residential environment.
With more than 60% of the land farmed, with vulnerable freshwater and marine environments, and with one of the most intensive, export-oriented livestock sectors in the world, the nitrogen (N) ...pollution pressure from Danish agriculture is severe. Consequently, a series of policy action plans have been implemented since the mid 1980s with significant effects on the surplus, efficiency and environmental loadings of N. This paper reviews the policies and actions taken and their ability to mitigate effects of reactive N (Nr) while maintaining agricultural production. In summary, the average N-surplus has been reduced from approximately 170 kg N ha−1 yr−1 to below 100 kg N ha−1 yr−1 during the past 30 yrs, while the overall N-efficiency for the agricultural sector (crop + livestock farming) has increased from around 20-30% to 40-45%, the N-leaching from the field root zone has been halved, and N losses to the aquatic and atmospheric environment have been significantly reduced. This has been achieved through a combination of approaches and measures (ranging from command and control legislation, over market-based regulation and governmental expenditure to information and voluntary action), with specific measures addressing the whole N cascade, in order to improve the quality of ground- and surface waters, and to reduce the deposition to terrestrial natural ecosystems. However, there is still a major challenge in complying with the EU Water Framework and Habitats Directives, calling for new approaches, measures and technologies to mitigate agricultural N losses and control N flows.
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