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A hierarchy of urban land definitions: urban area, builtup area, and impervious surface area. The numbers represent the best available estimates of the global urban land area around 2010, corresponding to each definition (see Table 2 for details). Antarctica and Greenland were excluded in calculating the percentage of the global urban land
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Urbanization has transformed the world’s landscapes, resulting in a series of ecological and environmental problems. To assess urbanization impacts and improve sustainability, one of the first questions that we must address is: how much of the world’s land has been urbanized? Unfortunately, the estimates of the global urban land reported in the lit...
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... avoid or eliminate the confusion due to various definitions, here we propose a three-level hierarchical system of urban land definitions (Fig. 1), which is a nested definitional hierarchy in the parlance of hier- archy theory (Wu 2013a). This framework consists of three hierarchical levels, corresponding to three key definitions of urban land with decreasing spatial inclusiveness: ''urban area'' at the bottom, ''built-up area'' in the middle, and ''impervious surface'' at the ...
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... (Fig. 1), which is a nested definitional hierarchy in the parlance of hier- archy theory (Wu 2013a). This framework consists of three hierarchical levels, corresponding to three key definitions of urban land with decreasing spatial inclusiveness: ''urban area'' at the bottom, ''built-up area'' in the middle, and ''impervious surface'' at the top (Fig. ...
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... is the ''impervious surface,'' which refers to human-made land covers through which water cannot penetrate, including rooftops, roads, driveways, sidewalks, and parking lots (Ridd 1995;Weng 2012). For a given geographic region, the impervious surface area must be smaller than the built-up area which, in turn, must be smaller than the urban area (Fig. 1). For example, Sutton et al. (2010) found that, in Southeast Asia, the fraction of impervious surface was often much less than 50 % of the built-up area even in the core of large ...
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... Pero los números, así como los conceptos, pueden ser elusivos. Varios relatos alternativos sobre la distinción entre ciudad y campo indicarían que el 3% de la tierra es urbana (Liu et al. 2014), mientras que el 38% es agrícola (FAO 2020). Y extenderían su evaluación al decir que Groenlandia, la Antártida, los glaciares y los casquetes polares, en conjunto, corresponderían al 10% de la Tierra, con un 49% restante que pertenecería a otros ambientes salvajes como selvas, desiertos y montañas. ...
El texto discute y cuestiona la validez de la dicotomía campo-ciudad —aún prevaleciente en el discurso arquitectónico— y los dilemas conceptuales que plantea en un momento en que el mundo se ha contraído a través de la velocidad de las telecomunicaciones, las redes satelitales, la hiperconectividad virtual del internet y los medios ultrarrápidos de transporte aéreo. Refutando el esquematismo de esta dicotomía, el artículo revisa la emergencia de una única área metropolitana global que incorpora, en su interior, lo que usualmente consideramos como lo no-urbano.
... In these studies on physical expansion and structural patterns of cities, remote sensing data is the core data source. The question of how urban areas should be delineated to provide a consistent spatial reference for comparative studies is the subject of considerable debate (see e. g. the works of Liu, He, Zhou, et al., 2014;Angel, Lamson-Hall, Galarza, & Blei, 2018;Melchiori et al., 2018;Dijkstra et al., 2021;Taubenböck et al., 2022;Inostroza & Taubenböck, 2024). Overall, the literature on urbanization is not consistent in their spatial references and comparisons within and between studies are therefore susceptible to statistical bias (e.g. ...
Cities are expanding all over the world. In this study we aim to understand how the pace and scale of urban growth dynamics vary across geographies. This study contributes to the literature in four key ways: First, the study is comprehensive including all 1567 cities worldwide that had >300,000 inhabitants in 2015. Second, comparison of settlement dynamics of cities is performed in relation to continents, to geographic regions, to national levels and to city sizes. Third, a data-driven approach to delineate city boundaries allows for consistent comparisons across geographies. Fourth, the measured past urban trends are projected into the future and linked to climate scenarios used by the Panel on Climate Change (IPCC) to estimate where spatial focal areas of urbanization and climate-change meet. The study is based on remote sensing-derived geodata such as the World Settlement Footprint Evolution dataset for the period 1985 to 2015 and morphological urban areas. The key findings are: At continental scale, highest relative urban growth rates are measured in Asia. Among the IPCC regions, highest relative urban growth rates are in East Asia. In contrast, lowest growth rates are in Oceania and Europe. As expected, across most regions, there is a general decline in relative growth rates over the study period. One surprising finding is that absolute settlement expansion rates are not declining over time, but are rather relatively constant. It is also interesting to see that across and within countries growth rates of urban settlements vary widely in Asia, whereas in Europe there are only marginal differences. And finally, a look into the future reveals that certain regions can expect particularly high exposures. In South Asia and West Africa, for example, very high urban growth rates and a very high increase in predicted maximum rainfall are forecast. The greatest increase in extreme temperatures is predicted for Europe and North America. Settlement growth has already slowed there, so adaptation measures are taking center stage.
... Heavy precipitation and flooding, as well as desertification and drought, all induced by climate change, are expected to increase soil compaction (Posthumus et al., 2009;Olagunju, 2015). Soil sealing due to rapid urbanization, combined with increased rainfall intensity due to climate change, will likely increase surface water runoff, erosion and floods, exacerbating land degradation processes (Pataki et al., 2011;Liu et al., 2014;IPBES, 2018;Olsson et al., 2019). Urbanization and soil sealing also raise local surface air temperatures in cities and their surroundings through the urban heat island effect (Jia et al., 2019). ...
Land use and land-use change (including related policies) interact with climate and climate change (including related policies) in multiple ways. Land-use sectors are among the most affected by climate change. They are also a significant source of greenhouse gas (GHG) emissions.According to the Intergovernmental Panel on Climate Change, agriculture, forestry and other land use are the second source of GHG emissions after fossil fuel use and account globally for about 23 percent of total net anthropogenic GHG emissions. However, the land use sectors are not only part of the problem, but also part of the solution. They are key to adaptation. The global potential of land-based mitigation options is evaluated at about 30 percent of the global mitigation effort required in 2050 to meet the 1.5 °C target of the Paris Agreement.This publication, resulting from a collaboration between FAO and the Center for International Forestry Research, lead centre of the CGIAR research programme on Forests, Trees and Agroforestry, aims to recall those complex interactions and to explore the opportunities to enhance the role of land use under theUnited Nations Framework Convention on Climate Change to advance climate change mitigation and adaptation.
... Although worldwide urbanization is predicted to continue reducing biodiversity in regions where expansive land conversions are expected in the coming decades (Fenoglio et al., 2020;Li et al., 2022;McKinney, 2002;Miller & Hobbs, 2002), the number of ecological studies investigating urban areas is lower than expected, based on the proportion of urbanized land (Martin et al., 2012). Globally, urban areas only account for about 3% of landcover (Liu et al., 2014). ...
The threat to biodiversity posed by urban expansion is well researched and supported. Since the late 1990s, the field of urban ecology has been expanding along with the developed landscapes it studies. Past reviews have shown unequal publication rates in urban ecology literature for taxonomic groups and research locations. Herein, we explore differences in the publication rate of urban studies by vertebrate groups, but also expand on previous investigations by broadening the scope of the literature searched, exploring trends in subtopics within the urban wildlife literature, identifying geographic patterns of such publications, and comparing the rate at which non‐native and threatened and endangered species are studied in urban settings. We used linear and segmented regression to assess publication rates and Fisher's exact tests for comparisons between groups. All vertebrate groups show an increasing proportion of urban studies through time, with urban avian studies accelerating most sharply and herpetofauna appearing to be understudied. Non‐native mammals are more studied than non‐native birds, and threatened and endangered herpetofauna and mammals are more likely to be studied than threatened and endangered birds in urban areas. The plurality of urban wildlife studies are found in North America, while there is a dearth of studies from Africa, Asia, and South America. Our results can help inform decisions of urban ecologists on how to better fill in knowledge gaps and bring a greater degree of equity into the field.
... These differences likely stem from different data characteristics, such as the spatial resolution or the type of satellite imagery employed for producing the datasets 30,[44][45][46] . In urban analyses the main issue involves the often unclear definition of 'urban' or 'built-up' , due to the lack of a consistent definition in the literature 7,47 . This complicates the comparison of the results of urban analyses 40,43,48 and raises the need for a harmonized approach to define distinct settlement types 40 . ...
Information on urban land use, beyond the urban-rural dichotomy, can improve the assessment of potential impacts of coastal hazards by refining estimates of damages and supporting adaptation planning. However, the lack of a consistent definition of “urban” in previous studies has led to exposure estimates that vary considerably. Here, we explore the sensitivity of exposed population and built-up area in four settlement types, defined by four different built-up area datasets. We find large differences in the exposed population of up to 65% (127 million people) in the “Urban” class. The exposure estimates are highly sensitive to the density thresholds used to distinguish the settlement types, with a difference in exposed urban population of up to 53.5 million people when the threshold varies by 10%. We attribute the high sensitivity of the exposure estimates to the varying definitions of built-up area of the underlying datasets. We argue that the definition of urban land is crucial for coastal impact assessments and make recommendations for the use of the analyzed datasets.
... While urban areas cover only a minuscule fraction of the Earth's terrestrial area, approximately 3 % as reported by Liu et al. (2014), they are home to more than 55 % of the global population, thereby exerting a substantial influence on global greenhouse gas (GHG) emissions (IPCC, 2022). The continued expansion of urban areas is projected to accommodate an estimated 68 % (approximately 6.7 billion people) of the world's population by 2050, driven by the ongoing trend of urbanization (UN, 2019). ...
Long-term tall-tower eddy-covariance (EC) measurements have been recently established in three European pilot cities as part of the ICOS-Cities project. We conducted a comparison of EC software to ensure a reliable generation of interoperable flux estimates, which is the prerequisite for avoiding methodological biases and improving the comparability of the results. We analyzed datasets covering 5 months collected from EC tall-tower installations located in urbanized areas of Munich, Zurich, and Paris. Fluxes of sensible heat, latent heat, and CO2 were calculated using three software packages (i.e., TK3, EddyPro, and eddy4R) to assess the uncertainty of flux estimations attributed to differences in implemented postprocessing schemes. A very good agreement on the mean values and standard deviations was found across all three sites, which can probably be attributed to a uniform instrumentation, data acquisition, and preprocessing. The overall comparison of final flux time series products showed a good but not yet perfect agreement among the three software packages. TK3 and EddyPro both calculated fluxes with low-frequency spectral correction, resulting in better agreement than between TK3 and the eddy4R workflow with disabled low-frequency spectral treatment. These observed flux discrepancies indicate the crucial role of treating low-frequency spectral loss in flux estimation for tall-tower EC systems.
... It also simplifies and homogenizes species composition (Mironova, Volkova, Gura, & Makar, 2022), disrupts hydrological systems (Arnold & Gibbons, 1996;Tayebi et al., 2022), and alters energy flow and nutrient cycling (Booth & Jackson, 1997;Modrzyński & Karaszewski, 2022;Wang, Van Dam, Triantafyllidis, Koppelaar, & Shah, 2017). Despite urban areas covering only a small portion of the total land surface (Liu, He, Zhou, & Wu, 2014;UNO, 2018), they consume a significant share of land's carrying capacity in terms of resource and energy consumption, waste generation, and pollutant emissions (OECD G20, 2021;Zheng, Xiao, You, Feng, & Zhiming, 2022). Cities rely on ecosystem services imported from distant regions and depend on global-scale ecological transformations. ...
... It also simplifies and homogenizes species composition (Mironova, Volkova, Gura, & Makar, 2022), disrupts hydrological systems (Arnold & Gibbons, 1996;Tayebi et al., 2022), and alters energy flow and nutrient cycling (Booth & Jackson, 1997;Modrzyński & Karaszewski, 2022;Wang, Van Dam, Triantafyllidis, Koppelaar, & Shah, 2017). Despite urban areas covering only a small portion of the total land surface (Liu, He, Zhou, & Wu, 2014;UNO, 2018), they consume a significant share of land's carrying capacity in terms of resource and energy consumption, waste generation, and pollutant emissions (OECD G20, 2021;Zheng, Xiao, You, Feng, & Zhiming, 2022). Cities rely on ecosystem services imported from distant regions and depend on global-scale ecological transformations. ...
... In spite of all these negative impacts, the cities house and provide economic welfare with over 4 billion people (nearly half of the world's population) while producing 80% of the global gross product. Although cities account only for 2-3% of earth's land surface, they consume more than 60% of global energy and produce 70% of greenhouse gas emissions and global waste (C40 Cities, 2012;Liu et al., 2014;United Nations, 2016) due to the increase in the number, size and population of (mega)cities (Demircan & Toy, 2019;Naboni et al., 2019;United Nations, 2018). If urbanization is managed well, it can contribute to sustainable growth and development, increase productivity, contribute to innovation and the development of new ideas (Sayad et al., 2021;United Nations, 2019). ...
Altered characteristics of urban microclimates elongating the daily and seasonal exposure periods to heat stress and enlarging the size of the thermal uncomfortable urban surfaces. This situation is human thermal comfort conditions negatively which in turn affect public health and wellbeing. The aim of this study is to determine the spatial distribution of thermal comfort conditions in the neighbourhood of Yakutiye, the center of Erzurum city over the hottest 2 months of the year (July and August) based on long term (2004–2020) meteorological data to show the impact of urban areas on thermal comfort conditions where structured surfaces are dominant. PET index was used to calculate thermal comfort conditions through RayMan model and ArcGIS 10.5 software for their spatial distribution. It was seen as the result of the study that solar radiation and wind are two effective factors on thermal comfort contrarily to each other depending on the characteristics of the city in the mentioned period. Overheating by solar radiation due to concrete structured urban surface is tolerated by north-easterly cool winds. However, lack of moisture source (i.e. green areas) to moderate heat and cold stress is one of the main causes of thermally uncomfortable periods and areas in the city center. In order to improve such negative conditions, mitigating efforts should be focused on creating city parts that comply with spatial planning and design principles, taking into account all natural and human factors from a geographical perspective.
... The world is facing a growing number of complex global issues, including climate change, global warming, public health, social equity, environmental problems such as ecosystem degradation, food security, as well as their cascading effects [1] and complex mechanisms and relationships [2,3]. Cities are particularly affected, with over 56% of the world's population living on just 3% of the Earth's land area in 2021; this figure is projected to increase to 68% by 2050 [4]. The COVID-19 pandemic and frequent extreme weather and natural disasters have also heightened concerns regarding urban resilience and sustainability [5] (pp. ...
Urban built environment professions are facing challenges due to the less predictable future of cities, as well as the increasing expectations from clients and the general public. It is crucial to support and inform these professions with sound evidence in order to promote the sustainability of cities. However, there have been few efforts to introduce evidence-based design (EBD) theories and frameworks into built environment professional education. This study presents an EBD framework for an undergraduate urban design studio. The effectiveness and long-term impact of EBD approaches and the framework presented were examined via learning outcomes, student reflections, and guest comments across two rounds of studio delivery. The reflections and comments were coded and analyzed using NVivo 11. The effectiveness of the EBD approach is confirmed for the premises, development, and effectiveness of urban design proposals that align with the concerns and expectations of professional guests. The wide range of evidence and techniques also fosters cross-disciplinary collaborations. This study sheds light on education in the built environment disciplines, which would further enhance the strength of relevant professions, ultimately contributing to the sustainability of society.
