Ecological security patterns (ESPs) aim to provide an effective spatial approach for maintaining urban ecological security based on the relationship between landscape patterns and ecological ...processes. However, the methods of selecting ecological security sources and evaluating resistance surfaces for ESPs construction are not well developed and lack consideration of land degradation and spatial heterogeneity. Using Shenzhen City, a fast-growing city in a rapidly urbanizing region, as a case study area, this study evaluated two types of land degradation risk for ecological land: type transformation risk and functional damage risk. Both two kinds of risk were combined with ecological functional importance, which was composed of habitat quality and landscape connectivity, so as to quantify the comprehensive reserve value of ecological land to identify the ecological security sources. Ecological corridors were established with the application of remotely-sensed impervious surface area in the ecological resistance surface evaluation. In all, 477.43 km2 ecological land were identified as ecological security sources, with 278.1 km and 197.5 km for the length of group corridors and landscape corridors respectively. The ecological corridors spatially presented a radiation pattern of one axis and three strips. The majority of both ecological security sources and corridors was located within the existing ecological protection boundary, confirming its ecological significance. This study provided an effective quantification framework to identify urban ESPs, and ESPs mapping could make a fundamental support to urban planning.
•Land cover proportion can almost substitute for area-related landscape configuration indicators.•Landscape composition has relatively stable correlation values at different scales.•Vegetated land ...surfaces composition is more indicative than unvegetated land surfaces.•Landscape metrics are better correlated with LST in high temperature than in low temperature.•Unvegetated land surfaces proportion weakly influences the correlations (R2 < 0.2).
Identification of the relationship between landscape metrics and urban land surface temperature (LST) provides a basic understanding of the interaction of landscape pattern and ecological process. However, the evidenced relationships between landscape metrics and LST are still uncertain, and cannot provide fundamental support to landscape management. Other than a test of statistical significance, four judgments (median correlation value; temporal variation and statistical scale; threshold; and effects of key variables) are considered “efficient” criteria in this study. Partial correlation and piecewise linear regression are used to focus on the indicators of land cover proportion, biophysical proportion, and mainly area- or shape-related landscape configuration indicators. The results show: (1) land cover proportion can almost substitute for area-related landscape configuration indicators; (2) landscape composition is more efficient than configuration as an indicator because of its relatively stable temporal correlation values at different statistical scales; (3) the evident landscape composition threshold of vegetated land surfaces (50–70% for land cover proportion and 0.2–0.3 for biophysical proportion) is more indicative in application than the linear relationship for unvegetated land surfaces; and (4) landscape metrics are better correlated with LST in high temperature than in low temperature, and urban area weakly influences this correlation (R2 < 0.2). Additionally, the configuration metrics at a landscape level are not recommended for characterizing LST. Depended on the efficient indicators, such as the application of thresholds, landscape planning can be linked to the quantitative observations and statistical evidence in landscape metrics.
•Arid cities among 40 African cities had greater urban tree CE.•CE increased and then decreased as AT/TDPD increased, with turning point of 34 °C/26 °C.•Sahel cities couldn’t cool only by trees since ...they would have more days over 34 ℃.
Urban tree cover is widely regarded as an environmentally-friendly and effective urban cooling approach. Meteorological variables, including air temperature, wind speed, and humidity, have complex impacts on the cooling efficiency (CE) of urban trees (i.e., the negative ratio of the land surface temperature change to the tree cover percentage change). This means that increasing the urban tree cover to alleviate heat stress is not necessarily suitable for cities with different climates. African cities are confronted with larger heat risks but lack considerations for the effectiveness of urban tree cooling in urban planning. In this study, 40 African major cities with population greater than 500,000 in different climatic regions were selected, and 1459 CEs during each city’s corresponding warmest 3 consecutive months were calculated combined with the availability of meteorological data. The generalized additive models revealed the non-linear impacts of air temperature/temperature dew point difference on CE, which were more evident in arid cities. The CE of urban trees actually increased and then decreased along with the increase of air temperature/temperature dew point difference, and the turning point were 34 °C/26 °C, respectively. African cities would have different frequencies of warm days with an air temperature over 34 °C under different Shared Socioeconomic Pathways within the next 30 years. Specially, the cities around Sahel would suffer up to 40–60% days over 34 °C, which meant their urban tree CE would decrease along with air temperature increase. This study highlighted that in African cities, especially those with arid climate, it was unadvisable to only count on increasing tree cover to alleviate urban heat stress in the warming future, which called for other combined cooling strategies.
Remotely sensed land surface temperature (LST) distribution has played a valuable role in land surface processes studies from local to global scales. However, it is still difficult to acquire ...concurrently high spatiotemporal resolution LST data due to the trade-off between spatial and temporal resolutions in thermal remote sensing. To address this problem, various methods have been proposed to enhance the resolutions of LST data, and substantial progress in this field has been achieved in recent years. Therefore, this study reviewed the current status of resolution enhancement methods for LST data. First, three groups of enhancement methods—spatial resolution enhancement, temporal resolution enhancement, and simultaneous spatiotemporal resolution enhancement—were comprehensively investigated and analyzed. Then, the quality assessment strategies for LST resolution enhancement methods and their advantages and disadvantages were specifically discussed. Finally, key directions for future studies in this field were suggested, i.e., synergy between process-driven and data-driven methods, cross-comparison among different methods, and improvement in localization strategy.
Context
Revealing the interaction between landscape pattern and urban land surface temperature (LST) can provide insight into mitigating thermal environmental risks. However, there is no consensus ...about the key landscape indicators influencing LST.
Objectives
This study sought to identify the key landscape indicators influencing LST considering a large number of landscape pattern variables and multiple scales.
Methods
This study applied ordinary least squares regression and partial least squares regression to explore a combination of landscape metrics and identify the key indicators influencing LST. A total of 49 Landsat images of the main city of Shenzhen, China were examined at 13 spatial scales.
Results
The landscape composition indicators derived from biophysical proportion, a new metric developed in this study, more effectively determined LST variation than those derived from land cover proportion. Area-related landscape configuration indicators independently characterized LST variation, but did not give much more new information beyond that given by land cover proportion. Shape-related landscape configuration indicators were effective in combination with land cover proportion, but their importance was uncertain when temporal and spatial scales varied.
Conclusions
The influence of landscape configuration on LST exists but should not be overestimated. Comparison of numerous variables at multiple spatiotemporal scales can help identify the influence of multiple landscape characteristics on LST variation.
Informal housing and industrial developments in the so‐called urban villages have been key features of the recent Chinese urbanization. In this article we will examine the development of urban ...villages in one of the most dynamic Chinese cities — Shenzhen. The article first reviews the urbanization and migration process in the region and the emergence of urban villages. It then examines informal housing, commercial and industrial developments in these villages. We analyse the politics of village urbanization and highlight the important relationship between migration and informal village development. We emphasize the contribution made by urban villages in providing affordable housing and jobs for the low‐income population during the rapid urbanization and urge cautious consideration with regard to hasty and large‐scale redevelopment of these villages. We conclude that the development of urban villages is a very important part of the urbanization process.
Résumé
L’habitat informel et les aménagements commerciaux et industriels dans les villages dits urbains constituent des caractéristiques essentielles de la récente urbanisation chinoise. Cet article examine le développement des villages urbains dans l’une des villes les plus dynamiques: Shenzhen. L’article revient d’abord sur les processus d’urbanisation et de migration dans la région et sur l’émergence des villages urbains. Il s’attache ensuite à l’habitat informel, ainsi qu’aux aménagements commerciaux et industriels, dans ces villages. La politique d’urbanisation des villages est analysée, mettant en évidence le lien important entre migration et aménagement informel des villages. L’étude souligne que les villages urbains fournissent des logements accessibles financièrement et des emplois à la population à faible revenu pendant la phase rapide d’urbanisation, et insiste sur les précautions à prendre vis‐à‐vis d’un réaménagement précipité et à grande échelle de ces villages. La conclusion met en avant combien le développement des villages urbains est important dans le processus d’urbanisation.
Unprecedented rapid urbanization in China during the past several decades has been accompanied by extensive urban landscape renewal, which has increased the urban thermal environmental risk. However, ...landscape change is a sufficient but not necessary condition for land surface temperature (LST) variation. Many studies have merely highlighted the correlation between landscape pattern and LST, while neglecting to comprehensively present the spatiotemporal diversification of LST change under urban landscape renewal. Taking the main city of Shenzhen as a case study area, this study tracked the landscape renewal and LST variation for the period 1987–2015 using 49 Landsat images. A decision tree algorithm suitable for fast landscape type interpretation was developed to map the landscape renewal. Analytical tools that identified hot-cold spots, the gravity center, and transect of LST movement were adopted to identify LST changes. The results showed that the spatial variation of LST was not completely consistent with landscape change. The transformation from Green landscape to Grey landscape usually increased the LST within a median of 0.2 °C, while the reverse transformation did not obviously decrease the LST (the median was nearly 0 °C). The median of LST change from Blue landscape to Grey landscape was 1.0 °C, corresponding to 0.5 °C in the reverse transformation. The imbalance of LST change between the loss and gain of Green or Blue landscape indicates the importance of protecting natural space, where the benefits in terms of temperature mitigation cannot be completely substituted by reverse transformation.
Changes in biodiversity owing to vegetation degradation resulting from widespread urbanization demands serious attention. However, the connection between vegetation degradation and urbanization ...appears to be complex and nonlinear, and deserves a series of long-term observations. On the basis of the Normalized Difference Vegetation Index (NDVI) and the image's digital number (DN) in nighttime stable light data (NTL), we delineated the spatiotemporal relations between urbanization and vegetation degradation of different metropolises by using a simplified NTL calibration method and Theil-Sen regression. The results showed clear and noticeable spatiotemporal differences. On spatial relations, rapidly urbanized cities were found to have a high probability of vegetation degradation, but in reality, not all of them experience sharp vegetation degradation. On temporal characteristics, the degradation degree was found to vary during different periods, which may depend on different stages of urbanization and climate history. These results verify that under the scenario of a vegetation restoration effort combined with increasing demand for a high-quality urban environment, the urbanization process will not necessarily result in vegetation degradation on a large scale. The positive effects of urban vegetation restoration should be emphasized since there has been an increase in demand for improved urban environmental quality. However, slight vegetation degradation is still observed when NDVI in an urbanized area is compared with NDVI in the outside buffer. It is worthwhile to pay attention to landscape sustainability and reduce the negative urbanization effects by urban landscape planning.
Urbanization has accelerated rapidly over the last century, which has caused surfaces in natural ecosystems to shift to impervious surfaces. As a result, urban watershed ecosystems show altered ...physical, chemical and ecological process. As an important part of watershed management, urbanization has become one of the key issues involved in the deterioration of water quality. Impervious surface area (ISA) has been recognized as a key indicator of the effects of non-point runoff and water quality within a particular watershed. Numerous case studies have been conducted to investigate the relationship between urbanization and water quality in different study areas. However, there is still a lack of understanding regarding quantitative analysis of the threshold between urbanization and water quality indicators. This study was conducted to improve the understanding of how to quantify a threshold between urbanization and water quality, taking the rapid urbanization zone of Shenzhen, China as a case study. To accomplish this, ISA was extracted from the Landsat™ image using a linear spectral mixture method to quantify the urbanization. The relationship between water quality indicators and ISA was then analyzed by nonlinear regression, and the threshold between ISA and the chemical indicators of water quality was investigated using the statistical segment approach method. The results indicate that the water quality indicators and ISA are significantly correlated, and that, with the exception of Zn, Pb, and CN, the water quality indicators had R ² values greater than 0.45. Furthermore, with the exception of Zn, F⁻, Pb and oils, water quality indicators were found to have an ISA threshold of 36.9–52.9 %, indicating that it is important to control the ISA below 36.9 % in urbanization watersheds to enable effective urban watershed management.
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