Many studies have explored the complex mechanisms of urban heat islands by examining the relationship between land surface temperature (LST) and greenspace spatial patterns. Few, however, have ...explored the relative contributions of greenspace spatial composition and configuration to LST using comparisons between cities. In this study, the authors sought to identify the relative contributions of greenspace spatial composition and configuration to LST and the stability mechanisms linking LST to greenspace at multiple locations. We looked at four highly-urbanized Chinese cities in a comparative study. Landsat 5/8 images for summer and winter were used to estimate LST and greenspace data were extracted from 0.5-m resolution imagery. The complex relationship between LST and greenspace spatial patterns was quantified and compared using a novel method that combines stepwise regression with hierarchical partitioning analysis concerning statistical size variations. The results indicated that greenspace spatial composition and configuration both consistently affect LST. However, the magnitude and significance of these relationships were very different. The combined contributions of the greenspace landscape metrics played a more critical role in determining LST than their independent contributions, especially in summer. However, the relative importance of spatial composition and spatial configuration was largely dependent on specific variables such as season or selected statistical grid size. The urban heat island (UHI) effect can be reduced not only by increasing the amount of greenspace, but also by optimizing greenspace spatial configuration; the latter is more effective than the former. Although scale dependence continued to be evident in our study, we were not able to confirm a universal “best” scale for analysis. This study extended our understanding of the complex mechanisms of UHI in the region with respect to seasonal and scale factors, and has provided valuable information to support UHI adaptation strategy development by urban planners.
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•Spatial pattern of heat and cool clusters shifted greatly with seasons.•Whether greenspace spatial composition or configuration is more important significantly depends on specific variables.•Joint contributions of landscape metrics of greenspace had stronger effects on LST variations.•“Best” scale in determining LST-greenspace relationship varied among cities.
As an important tropospheric trace gas and precursor of photochemical smog, the accumulation of NO2 will cause serious air pollution. China, as the largest developing country in the world, has ...experienced a large amount of NO2 emissions in recent decades due to the rapid economic growth. Compared with the traditional air pollution monitoring technology, the rapid development of the remote sensing monitoring method of atmospheric satellite has gradually become the critical technical means of global atmospheric environmental monitoring. To reveal the NO2 pollution situation in China, based on the latest NO2 products from Sentinel-5P TROPOMI, the spatial–temporal characteristics and impact factors of troposphere NO2 column concentration of mainland China in the past year (February 2018 to January 2019) were analyzed on two administrative levels for the first time. Results show that the monthly fluctuation of tropospheric NO2 column concentration has obvious characteristics of “high in winter and low in summer”, while the spatial distribution forms a “high in East and low in west” pattern, bounded by Hu Line. The comparison of Coefficient of Variation (CV) and spatial autocorrelation models at two kinds of administrative scales indicates that although the spatial heterogeneity of NO2 column concentration is less affected by the observed scale, there is a “delayed effect” of about one month in the process of NO2 column concentration fluctuation. Besides, the impact factors analysis based on Spatial Lag Model (SLM) and Geographic Weighted Regression (GWR) reveals that there is a positive correlation between nighttime light intensity, the secondary and tertiary industries proportion and NO2 column concentration. Furthermore, for regions with serious NO2 pollution in North China Plain, the whole society electricity consumption and vehicle ownership also play a positive role in increasing the NO2 column concentration. This study will enlighten the government and policy makers to formulate policies tailored to local conditions, to more effectively implement NO2 emission reduction and air pollution prevention.
The regions near the Tropic of Cancer are a latitudinal geographical zone with typical climatic, topographic, and human landscape features. It is necessary to explore the region’s net primary ...productivity (NPP) dynamics as it combines complex topography, various vegetation types, and intense human activities. The study sets the transect near the Tropic of Cancer (TCT) and uses the Carnegie–Ames–Stanford (CASA) model to estimate the NPP from 2000 to 2020. After using the RESTREND method, the paper calculates and compares the relative contributions of climate variability and anthropogenic activities to NPP changes. Finally, the geographical detector (Geodetector) model is applied to evaluate how anthropogenic and natural factors affect spatial distribution patterns and NPP changes. The results indicated that the average annual NPP is 820.39 gC·m−2·yr−1 during the 21 years. In addition, when the NPP varies, it increases over the entire study area, with a slope of 4.81 gC·m−2·yr−1, particularly in the western region. Across the entire research area, 63.39% and 77.44% of the total pixels positively contribute to climate variability and human activities in NPP, with a contribution of 0.90 and 3.91 gC·m−2·yr−1, respectively. Within the western, central, and eastern regions, anthropogenic activities have a stronger impact on NPP than climate variability, particularly pronounced in the eastern region. Furthermore, vegetation cover is the dominant factor in the spatial patterns and NPP trends across the TCT and the three regions. In contrast, climate factors are shown to be less influential in NPP distribution than in the western region. The results also demonstrated that the effect of population density and the GDP on NPP gradually rises. Two-factor interaction is much larger than any individual factor, with the dominant interaction factor being vegetation cover with climatic factors. Lastly, the findings revealed that anthropogenic activities positively promote NPP accumulation across the TCT, thus highlighting the importance of human activity-led ecological restoration and ecological protection measures that contribute to regional carbon sequestration and carbon balance.
•Quantitative assessment of spatial and temporal changes of coupling relation between human footprint and ecosystem service value in Pearl River Delta Urban Agglomeration.•The coupling between human ...footprint and ecosystem service value shows a “core-periphery” dichotomy.•The expansion of Quadrant IV indicates the continuation of the urbanization process in Pearl River Delta Urban Agglomeration.•The synergistic change relationship between human footprint and its coupling index with ecosystem service value shows an inverted U-shaped curve.
Ecosystems provide multiple benefits that humans depend on for survival. However, humans severely affect ecosystems through urban sprawl and pollution, and ecosystem functions are therefore constrained. In order to explore the evolution of the human-ecosystem relationship and changes in ecological conditions in highly urbanized areas, this study takes the Pearl River Delta Urban Agglomeration (PRDUA) as the study area, and the ecosystem service values (ESV) and the human footprint (HF) index during 2000–2020 were evaluated. We also employed the four-quadrant model and coupling index to reveal the synergistic relationship and interaction intensity between ESV and HF. Results showed: (1) From 2000 to 2020, the core area of PRDUA exhibited low ESV and high HF, while the peripheral area presented high ESV and low HF. Temporally, over 46% of the PRDUA took on high and very high levels of HF during 2000–2020. ESV declined by over 9% in all 9 cities in the PRDUA. (2) Most of the PRDUA areas were in Quadrants II and IV, and the proportion of these two quadrants increased by 4.4% and 4.5% during 2000–2020, respectively. This indicates that the urbanization process is still ongoing in the PRDUA. The area in Quadrant IV had the lowest coupling index of 0.678 on average during 2000–2020, indicating that the interaction intensity between HF and ESV was significantly lower than in the other areas. (3) The relationship between HF and the coupling index showed an inverted U-shaped curve. This indicates that during urbanization, as human activity intensity grows, the intensity of human-ecosystem interaction increases and then turns down when it reaches a certain threshold. By revealing the changes in the human-ecosystem relationship in a highly urbanized area, this study provides theoretical guidance for ecological regulation and planning in such areas.
The spatiotemporal changes of open-surface water bodies in the Yangtze River Basin (YRB) have profound influences on sustainable economic development, and are also closely relevant to water scarcity ...in China. However, long-term changes of open-surface water bodies in the YRB have remained poorly characterized. Taking advantage of the Google Earth Engine (GEE) cloud platform, this study processed 75,593 scenes of Landsat images to investigate the long-term changes of open-surface water bodies in the YRB from 1984 to 2018. In this study, we adopted the percentile-based image composite method to collect training samples and proposed a multiple index water detection rule (MIWDR) to quickly extract the open-surface water bodies. The results indicated that (1) the MIWDR is suitable for the long-term and large-scale Landsat water bodies mapping, especially in the urban regions. (2) The areas of permanent water bodies and seasonal water bodies were 29,076.70 km2 and 21,526.24 km2, accounting for 57.46% and 42.54% of the total open-surface water bodies in the YRB, respectively. (3) The permanent water bodies in the YRB increased along with the decreases in the seasonal water bodies from 1984 to 2018. In general, the total open-surface surface water bodies in the YRB experienced an increasing trend, with an obvious spatial heterogeneity. (4) The changes of open-surface water bodies were associated with the climate changes and intense human activities in the YRB, however, the influences varied among different regions and need to be further investigated in the future.
•We extracted urban heat island (UHI) clusters using an innovative approach.•We examined the nonlinear relationships between the LST and urban biophysical composition in UHI clusters.•The spatial ...heterogeneity of the landscape within UHI results in the complexity of LST.•Both NDVI and NDBI are great indicators for predicting the variations of LST in UHI clusters.
The spatio-temporal pattern of biophysical composition significantly affects land surface temperature (LST). Previous studies, however, mostly characterized urban heat island (UHI) clusters being spatially homogeneous. The landscape spatial heterogeneity in urban across UHI clusters challenges us to more accurately characterize the relationships between LST and corresponding urban biophysical composition. In this study, we introduced an innovative integrated approach that combined object-oriented image segmentation with local indicators of spatial autocorrelations (LISA) to extract UHI clusters from an LST image. We used a regression tree model to examine the nonlinear relationships between LST and each of three satellite-based indices within the UHI clusters: normalized differential vegetation index (NDVI), normalized differential build-up index (NDBI), and normalized difference bareness index (NDBaI). We found that both NDVI and NDBI are strongly correlated with the variations of LST whereas NDBaI has a weaker correlation with LST. We also found that the regression tree model built in this study enabled us to effectively detect the nonlinear relationship between LST and biophysical composition. Furthermore, based on a set of rules derived from a regression tree analysis, we found that urban landscapes strongly affect LST and its spatial heterogeneity within a UHI. These rules were used to detect the nonlinear impacts of complex urban biophysical composition on LST. The results of this study provided insights into how LST within UHI varies with urban surface characteristics at fine spatial scale and also a new method for investigating effects of land surface composition on LST in urbanized areas.
This three-decade long study was conducted in the Pearl River Delta (PRD), a rapidly urbanizing region in southern China. Extensive soil samples for a diverse land uses were collected in 1989 (113), ...2005 (1384), 2009 (521), and 2018 (421) for heavy metals of As, Cr, Cd, Cu, Hg, Ni, Pb and Zn. Multiple pollution indices and Structural Equation Models (SEMs) were used in attribution analysis and comprehensive assessments. Data showed that majority of the sampling sites was contaminated by one or more heavy metals, but pollutant concentrations had not reached levels of concerns for food security or human health. There was an increasing trend in heavy metal contamination over time and the variations of soil contamination were site-, time- and pollutant-dependent. Areas with high concentrations of heavy metals overlapped with highly industrialized and populated areas in western part of the study region. A dozen SEMs path analyses were used to compare the relative influences of key environmental factors on soil contamination across space and time. The high or elevated soil contaminations by As, Cr, Ni, Cu and Zn were primarily affected by soil properties during the study period, except 1989–2005, followed by land use patterns. Parent materials had a significant effect on elevated soil contamination of Cd, Cr, Ni, Pb and overall soil pollution during 1989–2005. We hypothesized that other factors not considered in the present study, such as atmospheric deposition, sewage irrigation, and agrochemical uses, may be also important to explain the variability of soil contamination. This study implied that strategies to improve soil physiochemical properties and optimize landscape structures are viable methods to mitigate soil contamination. Future studies should monitor pollutant sources identified by this study to fully understand the causes of heavy metal contamination in rapidly industrialized regions in southern China.
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•Regional soil samples were collected over a 3-decade period in southern China.•Majority of soil samples were polluted with multiple heavy metals.•Soil contamination elevated over time mostly in populated and industrialized area.•Anthropogenic factors overwhelmed parent materials in affecting soil pollution.•Improving soil properties and landscape pattern have potentials to reduce pollution.
Human activities overwhelmed parent materials in affecting soil contamination across space and over time in Pearl River Delta, southern China.
•The effect of tree coverage and microtopography on air temperatures was quantified.•Cooling capacity of the green space was positively correlated with total leaf area.•Microtopographic modification ...can enhance the cooling effect on adjacent open space.•Slope angle of microtopography control the extending cooling rate from the green space.
The tree coverage of a green space strongly influences its cooling effects; however, knowledge about how the cooling capacity extends beyond a given green space remains limited, along with how modifications to micro-topography affect local thermal environments. Here, we aimed to clarify the cooling effects within and beyond a green space by systematically evaluating differing tree coverage and micro-topographic conditions. Specifically, idealized scenarios were designed and simulated using the micro-climate model ENVI-met. We found that both canopy size and tree number clearly influenced thermal environment conditions within and outside a green space during the daytime. The cooling capacity of the green space during the daytime was linearly correlated with the total leaf area of trees. We also found that modifications to micro-topography had stronger cooling effects on both the green space and adjacent open space in contrast to flat terrain scenarios. Increasing the connectivity of impervious spaces and green areas, along with appropriate micro-topographic modifications, could prevent surrounding impervious surfaces from becoming micro-scale heat islands during the daytime; thus, ameliorating heat stress conditions. The results of this research provide a baseline for climate-adaptive designs and planning of thermally comfortable urban landscapes in the future.
Urban green infrastructures (UGI) can effectively reduce surface runoff, thereby alleviating the pressure of urban waterlogging. Due to the shortage of land resources in metropolitan areas, it is ...necessary to understand how to utilize the limited UGI area to maximize the waterlogging mitigation function. Less attention, however, has been paid to investigating the threshold level of waterlogging mitigation capacity. Additionally, various studies mainly focused on the individual effects of UGI factors on waterlogging but neglected the interactive effects between these factors. To overcome this limitation, two waterlogging high-risk coastal cities—Guangzhou and Shenzhen, are selected to examine the effectiveness and stability of UGI in alleviating urban waterlogging. The results indicate that the impact of green infrastructure on urban waterlogging largely depends on its area and biophysical parameter. Healthier or denser vegetation (superior ecological environment) can more effectively intercept and store rainwater runoff. This suggests that while increasing the area of UGI, more attention should be paid to the biophysical parameter of vegetation. Hence, the mitigation effect of green infrastructure would be improved from the “size” and “health”. The interaction of composition and spatial configuration greatly enhances their individual effects on waterlogging. This result underscores the importance of the interactive enhancement effect between UGI composition and spatial configuration. Therefore, it is particularly important to optimize the UGI composition and spatial pattern under limited land resource conditions. Lastly, the effect of green infrastructure on waterlogging presents a threshold phenomenon. The excessive area proportions of UGI within the watershed unit or an oversized UGI patch may lead to a waste of its mitigation effect. Therefore, the area proportion of UGI and its mitigation effect should be considered comprehensively when planning UGI. It is recommended to control the proportion of green infrastructure at the watershed scale (24.4% and 72.1% for Guangzhou and Shenzhen) as well as the area of green infrastructure patches (1.9 ha and 2.8 ha for Guangzhou and Shenzhen) within the threshold level to maximize its mitigation effect. Given the growing concerns of global warming and continued rapid urbanization, these findings provide practical urban waterlogging prevention strategies toward practical implementations.
•Applying InVEST model to determine ecological sources.•Building ecological resistance surfaces for highly urbanized region.•Proposing a local evaluation model for ecological networks.•Summarizing ...the ecological network development suggestions.
Metropolitan regions usually encounter sustainability difficulties such as overexploitation of resources, severe land scarcity, and ecological degradation, resulting in the progressive collapse of ecological networks (ENs). It is therefore essential to strengthen the construction and protection of ENs by integrating various resources, improving the quality of the urban ecological environment and creating a favourable living environment. Using the Guangdong-Hong Kong-Macao Greater Bay Area as a case study, in this paper, the ecological resistance indicator system that balances natural condition and human disturbance is rebuilt. In doing so, a construction scheme (applicable to highly urbanised areas) is established to simulate ENs at a more precise scale. Moreover, a local evaluation model of ENs is proposed and the spatial patterns of multiple indicators are fully summarised. The findings show that the ENs of the Guangdong-Hong Kong-Macao Greater Bay Area exhibit apparent spatial disparity. Disturbance through human activities seriously affects the spatial pattern of ENs, leading to structural imbalance and quality impairment of ecological corridors. Based on our assessment, the construction of complementary ecological corridors in the “two green belts” planning of the Guangdong-Hong Kong-Macao Greater Bay Area will improve structural problems. The findings of this paper can provide a reference to the harmonisation of urban development and ecological protection, by guiding the scientific management of ecological spaces in highly urbanised regions.
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