Showing papers on "Urban climate published in 2011"

A Meta-Analysis of Global Urban Land Expansion

Abstract: The conversion of Earth's land surface to urban uses is one of the most irreversible human impacts on the global biosphere. It drives the loss of farmland, affects local climate, fragments habitats, and threatens biodiversity. Here we present a meta-analysis of 326 studies that have used remotely sensed images to map urban land conversion. We report a worldwide observed increase in urban land area of 58,000 km2 from 1970 to 2000. India, China, and Africa have experienced the highest rates of urban land expansion, and the largest change in total urban extent has occurred in North America. Across all regions and for all three decades, urban land expansion rates are higher than or equal to urban population growth rates, suggesting that urban growth is becoming more expansive than compact. Annual growth in GDP per capita drives approximately half of the observed urban land expansion in China but only moderately affects urban expansion in India and Africa, where urban land expansion is driven more by urban population growth. In high income countries, rates of urban land expansion are slower and increasingly related to GDP growth. However, in North America, population growth contributes more to urban expansion than it does in Europe. Much of the observed variation in urban expansion was not captured by either population, GDP, or other variables in the model. This suggests that contemporary urban expansion is related to a variety of factors difficult to observe comprehensively at the global level, including international capital flows, the informal economy, land use policy, and generalized transport costs. Using the results from the global model, we develop forecasts for new urban land cover using SRES Scenarios. Our results show that by 2030, global urban land cover will increase between 430,000 km2 and 12,568,000 km2, with an estimate of 1,527,000 km2 more likely.

The Urban Climate

Abstract: The Urban Climate aims to summarize analytical studies directed toward physical understanding of the rural-urban differences in the atmospheric boundary layer. Attempts to quantify conditions have met with some success. There is certainly a clear understanding of the physical relations that create the climatic differences of urbanized areas. Although some of the earlier classical studies are cited here, the emphasis is on the work done during the last decade and a half. This volume comprises 11 chapters, beginning with an introductory chapter discussing the literature surrounding the topic, its historical development, and the problem of local climate modification. The second chapter presents an assessment of the urban atmosphere on a synoptic and local scale, and examines the observational procedures involved. The following chapters then go on to discuss urban air composition; urban energy fluxes; the urban heat island; the urban wind field; models of urban temperature and wind fields; moisture, clouds, and hydrometeors; urban hydrology; special aspects of urban climate; and finally, urban planning. This book will be of interest to practitioners in the fields of meteorology, urban planning, and urban climatology.

Urban growth, climate change, and freshwater availability

Abstract: Nearly 3 billion additional urban dwellers are forecasted by 2050, an unprecedented wave of urban growth. While cities struggle to provide water to these new residents, they will also face equally unprecedented hydrologic changes due to global climate change. Here we use a detailed hydrologic model, demographic projections, and climate change scenarios to estimate per-capita water availability for major cities in the developing world, where urban growth is the fastest. We estimate the amount of water physically available near cities and do not account for problems with adequate water delivery or quality. Modeled results show that currently 150 million people live in cities with perennial water shortage, defined as having less than 100 L per person per day of sustainable surface and groundwater flow within their urban extent. By 2050, demographic growth will increase this figure to almost 1 billion people. Climate change will cause water shortage for an additional 100 million urbanites. Freshwater ecosystems in river basins with large populations of urbanites with insufficient water will likely experience flows insufficient to maintain ecological process. Freshwater fish populations will likely be impacted, an issue of special importance in regions such as India's Western Ghats, where there is both rapid urbanization and high levels of fish endemism. Cities in certain regions will struggle to find enough water for the needs of their residents and will need significant investment if they are to secure adequate water supplies and safeguard functioning freshwater ecosystems for future generations.

A systematic review and scientific critique of methodology in modern urban heat island literature

Abstract: In the modern era of urban climatology, much emphasis has been placed on observing and documenting heat island magnitudes in cities around the world. Urban climate literature consequently boasts a remarkable accumulation of observational heat island studies. Through time, however, methodologists have raised concerns about the authenticity of these studies, especially regarding the measurement, definition and reporting of heat island magnitudes. This paper substantiates these concerns through a systematic review and scientific critique of heat island literature from the period 1950–2007. The review uses nine criteria of experimental design and communication to critically assess methodological quality in a sample of 190 heat island studies. Results of this assessment are discouraging: the mean quality score of the sample is just 50 percent, and nearly half of all urban heat island magnitudes reported in the sample are judged to be scientifically indefensible. Two areas of universal weakness in the literature sample are controlled measurement and openness of method: one-half of the sample studies fail to sufficiently control the confounding effects of weather, relief or time on reported ‘urban’ heat island magnitudes, and three-quarters fail to communicate basic metadata regarding instrumentation and field site characteristics. A large proportion of observational heat island literature is therefore compromised by poor scientific practice. This paper concludes with recommendations for improving method and communication in heat island studies through better scrutiny of findings and more rigorous reporting of primary research. Copyright © 2010 Royal Meteorological Society

Initial results from Phase 2 of the international urban energy balance model comparison

Abstract: Urban land surface schemes have been developed to model the distinct features of the urban surface and the associated energy exchange processes. These models have been developed for a range of purposes and make different assumptions related to the inclusion and representation of the relevant processes. Here, the first results of Phase 2 from an international comparison project to evaluate 32 urban land surface schemes are presented. This is the first large-scale systematic evaluation of these models. In four stages, participants were given increasingly detailed information about an urban site for which urban fluxes were directly observed. At each stage, each group returned their models' calculated surface energy balance fluxes. Wide variations are evident in the performance of the models for individual fluxes. No individual model performs best for all fluxes. Providing additional information about the surface generally results in better performance. However, there is clear evidence that poor choice of parameter values can cause a large drop in performance for models that otherwise perform well. As many models do not perform well across all fluxes, there is need for caution in their application, and users should be aware of the implications for applications and decision making. Copyright  2010 Royal Meteorological Society

Climate Change and Cities: First Assessment Report of the Urban Climate Change Research Network

Abstract: Forewords Acknowledgements Executive summary 1. Introduction Part I. Defining the Risk Framework: 2. Cities, disasters and climate risk 3. Urban climate: processes, trends and projections Part II. Urban Sectors: 4. Climate change and urban energy systems 5. Climate change, water and wastewater 6. Climate change and urban transportation systems 7. Climate change and human health in cities Part III. Cross-Cutting Issues: 8. The role of urban land in climate change 9. Cities and climate change: the challenges for governance Annex: list of contributors Index.

What makes an urban bird

Abstract: Urban development is increasing across the globe. This poses a major threat to biodiversity, which is often relatively poor in towns and cities. Despite much interest in identifying species' traits that can predict their responses to environmental degradation this approach has seldom been used to assess which species are particularly vulnerable to urban development. Here we explore this issue, exploiting one of the best available datasets on species' responses to towns and cities in a highly urbanized region, comprising avian densities across approximately 3000 British urban and rural 1 km x 1 km grid cells. We find that the manner in which species' responses to urbanization is measured has a marked influence on the nature of associations between these responses and species' ecological and life history traits. We advocate that future studies should use continuous indices of responses that take relative urban and rural densities into account, rather than using urban densities in isolation, or a binary response recording the presence/ absence of a species in towns and cities. Contrary to previous studies we find that urban development does not select against avian long-distance migrants and insectivores, or species with limited annual fecundity and dispersal capacity. There was no evidence that behavioural flexibility, as measured by relative brain size, influenced species' responses to urban environments. In Britain, generalist species, as measured by niche position rather than breadth, are favoured by urban development as are, albeit to a lesser extent, those that feed on plant material and nest above the ground. Our results suggest that avian biodiversity in towns and cities in urbanizing regions will be promoted by providing additional resources that are currently scarce in urban areas, and developing suitable environments for ground-nesting species.

Diversifying European agglomerations: evidence of urban population trends for the 21st century

Abstract: The beginning of the 21st century marks the first time in history that more than half of the world's population lives in urban areas. In Europe, more than 70% of the population lives in urban areas today. This number is likely to increase to 84% by 2050. However, a shift from growth to decline of urban population is already present for a growing number of cities. The paper examines urban population trends for 158 European agglomerations and assesses the dynamics behind one particular development of growth or decline. Using data from 1991 to 2004, we present statistical evidence of diversifying population trajectories for core cities and fringe areas. The quantitative results are contrasted with the widespread accepted cyclical urbanisation model that has been expounded as a theoretical approach to describe previous and future stages of European urban development. The structural approach of the model is discussed because we believe that such concepts do not reflect the dynamics of present urban development in Europe. The paper argues that the urban agglomerations studied do not show a single evolutionary stage of urban development. Rather, we found a coexistence of intensifying suburbanisation and developing reurbanisation, which is mainly driven by younger households. Copyright © 2009 John Wiley & Sons, Ltd.

Including the urban heat island in spatial heat health risk assessment strategies: a case study for Birmingham, UK

Abstract: Heatwaves present a significant health risk and the hazard is likely to escalate with the increased future temperatures presently predicted by climate change models. The impact of heatwaves is often felt strongest in towns and cities where populations are concentrated and where the climate is often unintentionally modified to produce an urban heat island effect; where urban areas can be significantly warmer than surrounding rural areas. The purpose of this interdisciplinary study is to integrate remotely sensed urban heat island data alongside commercial social segmentation data via a spatial risk assessment methodology in order to highlight potential heat health risk areas and build the foundations for a climate change risk assessment. This paper uses the city of Birmingham, UK as a case study area. When looking at vulnerable sections of the population, the analysis identifies a concentration of "very high" risk areas within the city centre, and a number of pockets of "high risk" areas scattered throughout the conurbation. Further analysis looks at household level data which yields a complicated picture with a considerable range of vulnerabilities at a neighbourhood scale. The results illustrate that a concentration of "very high" risk people live within the urban heat island, and this should be taken into account by urban planners and city centre environmental managers when considering climate change adaptation strategies or heatwave alert schemes. The methodology has been designed to be transparent and to make use of powerful and readily available datasets so that it can be easily replicated in other urban areas.

Quantifying urban heat island effects and human comfort for cities of variable size and urban morphology in the Netherlands

Abstract: [1] This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of small to large cities and villages in the Netherlands. To date, this subject has not been substantially studied in the Netherlands, since it has a relatively mild oceanic (Cfb) climate and impact was assumed to be minor. To fill this knowledge gap, this paper reports on observations of a selected network of reliable hobby meteorologists, including several in The Hague and Rotterdam. A number of alternative measures were also used to quantify UHI, i.e., the generalized extreme value distribution and return periods of UHI and adverse human comfort; its uncertainties were estimated by the statistical method of bootstrapping. It appeared essential to distinguish observations made at roof level from those made within the urban canyon, since the latter related more closely to exposure at pedestrian level and to urban canyon properties in their close neighborhood. The results show that most Dutch cities experience a substantial UHI, i.e., a mean daily maximum UHI of 2.3 K and a 95 percentile of 5.3 K, and that all cities experience a shadow effect in the morning when cities remain cooler than the rural surroundings. Also, an evident relation between the median of the daily maximum UHI and its 95 percentile was discovered. Furthermore, the 95 percentile of the UHI appears well correlated with population density. In addition, we find a significant decrease of UHI and the percentage of surface area covered by green vegetation, but the relation with open water remains unclear.

Global to city scale urban anthropogenic heat flux: model and variability

Abstract: The large scale urban consumption of energy (LUCY) model simulates all components of anthropogenic heat flux (QF) from the global to individual city scale at 2.5 × 2.5 arc-minute resolution. This includes a database of different working patterns and public holidays, vehicle use and energy consumption in each country. The databases can be edited to include specific diurnal and seasonal vehicle and energy consumption patterns, local holidays and flows of people within a city. If better information about individual cities is available within this (open-source) database, then the accuracy of this model can only improve, to provide the community data from global-scale climate modelling or the individual city scale in the future. The results show that QF varied widely through the year, through the day, between countries and urban areas. An assessment of the heat emissions estimated revealed that they are reasonably close to those produced by a global model and a number of small-scale city models, so results from LUCY can be used with a degree of confidence. From LUCY, the global mean urban QF has a diurnal range of 0.7–3.6 W m−2, and is greater on weekdays than weekends. The heat release from building is the largest contributor (89–96%), to heat emissions globally. Differences between months are greatest in the middle of the day (up to 1 W m−2 at 1 pm). December to February, the coldest months in the Northern Hemisphere, have the highest heat emissions. July and August are at the higher end. The least QF is emitted in May. The highest individual grid cell heat fluxes in urban areas were located in New York (577), Paris (261.5), Tokyo (178), San Francisco (173.6), Vancouver (119) and London (106.7). Copyright © 2010 Royal Meteorological Society

Monitoring urban expansion and land use/land cover changes of Shanghai metropolitan area during the transitional economy (1979–2009) in China

Abstract: This study explored the spatio-temporal dynamics and evolution of land use/cover changes and urban expansion in Shanghai metropolitan area, China, during the transitional economy period (1979–2009) using multi-temporal satellite images and geographic information systems (GIS). A maximum likelihood supervised classification algorithm was employed to extract information from four landsat images, with the post-classification change detection technique and GIS-based spatial analysis methods used to detect land-use and land-cover (LULC) changes. The overall Kappa indices of land use/cover change maps ranged from 0.79 to 0.89. Results indicated that urbanization has accelerated at an unprecedented scale and rate during the study period, leading to a considerable reduction in the area of farmland and green land. Findings further revealed that water bodies and bare land increased, obviously due to large-scale coastal development after 2000. The direction of urban expansion was along a north-south axis from 1979 to 2000, but after 2000 this growth changed to spread from both the existing urban area and along transport routes in all directions. Urban expansion and subsequent LULC changes in Shanghai have largely been driven by policy reform, population growth, and economic development. Rapid urban expansion through clearing of vegetation has led to a wide range of eco-environmental degradation.

Urban climatic map studies: a review

Abstract: Since their introduction 40 years ago, worldwide interest in urban climatic map (UCMap) studies has grown. Today, there are over 15 countries around the world processing their own climatic maps, developing urban climatic guidelines, and implementing mitigation measures for local planning practices. Facing the global issue of climate change, it is also necessary to include the changing climatic considerations holistically and strategically in the planning process, and to update city plans. This paper reviews progress in UCMap studies. The latest concepts, key methodologies, selected parameters, map structure, and the procedures of making UCMaps are described in the paper. The mitigation measures inspired by these studies and the associated urban climatic planning recommendations are also examined. More than 30 relevant studies around the world have been cited, and both significant developments and existing problems are discussed. The thermal environment and air ventilation condition within the urban canopy layer (UCL) of the city are important in the analytical processes of the climatic-environmental evaluation. Possible mitigation measures and planned actions include decreasing anthropogenic heat release, improving air ventilation at the pedestrian level, providing more shaded areas, increasing greenery, creating air paths, and controlling building morphologies. Further developments have and will continue to focus on the spatial analysis of human thermal comfort in urban outdoor environments and on the impacts and adaptations of climate change. Mapmakers must continue to share lessons and experiences with city planners and policy makers, especially in the rapidly expanding cities of developing countries and regions. Copyright © 2010 Royal Meteorological Society

Observing and modeling the nocturnal park cool island of an arid city: horizontal and vertical impacts

Abstract: We examined the horizontal and vertical nocturnal cooling influence of a small park with irrigated lawn and xeric surfaces (∼3 ha) within a university campus of a hot arid city. Temperature data from 0.01- to 3-m heights observed during a bicycle traverse of the campus were combined with modeled spatial temperature data simulated from a three-dimensional microclimate model (ENVI-met 3.1). A distinct park cool island, with mean observed magnitudes of 0.7–3.6°C, was documented for both traverse and model data with larger cooling intensities measured closer to surface level. Modeled results possessed varying but generally reasonable accuracy in simulating both spatial and temporal temperature data, although some systematic errors exist. A combination of several factors, such as variations in surface thermal properties, urban geometry, building orientation, and soil moisture, was likely responsible for influencing differential urban and non-urban near-surface temperatures. A strong inversion layer up to 1 m over non-urban surfaces was detected, contrasting with near-neutral lapse rates over urban surfaces. A key factor in the spatial expansion of the park cool island was the advection of cooler park air to adjacent urban surfaces, although this effect was mostly concentrated from 0- to 1-m heights over urban surfaces that were more exposed to the atmosphere.

Dynamics of Urbanization and Its Impact on Land-Use/Land-Cover: A Case Study of Megacity Delhi

Abstract: The rapid expansion of urban areas due to rise in population and economic growth is increasing additional demand on natural resources thereby causing land-use changes especially in megacities. Therefore, serious problems associated with rapid development such as additional infrastructure, informal settlements, environmental pollution, destruction of ecological structure and scarcity of natural resources has been studied carefully using remote sensing and GIS technologies for a rapidly grown megacity namely, Delhi. The present work evaluates the land use/land cover (LULC) changes and urban expansion in Mega city Delhi and highlights the major impact of rapid urbanization and population growth on the land cover changes which needs immediate attention. The results indicate that the city is expanding towards its peripheral region with the conversion of rural regions in to urban expansions. Built-up area of Delhi witnessed an overall increment from 540.7 km² to 791.96 km² or 16.86% of the total city area (1,490 km² ) during the study period 1997 to 2008 which mainly came from agriculture land, waste land, scrub-land, sandy areas and water bodies. The increment in forest cover of 0.5 % is very small when considering the increment in built up category to 17%. Total area of waterbodies has reduced by 52.9% in a ten year period (58.26 km² in 1997 to 27.43 km² in 2008) with shallow waterbodies now having a dismal presence. LULC changes are studied with the urban growth parameters such as population, vehicles, gross state domestic product etc. The results lay emphasis on the concepts of urban planning to be applied such that more consideration is towards the preservation and management of natural land use classes which will increase the quality of life in an urban environment.

Urban Sprawl Analysis and Modeling in Asmara, Eritrea

Abstract: The extension of urban perimeter markedly cuts available productive land. Hence, studies in urban sprawl analysis and modeling play an important role to ensure sustainable urban development. The urbanization pattern of the Greater Asmara Area (GAA), the capital of Eritrea, was studied. Satellite images and geospatial tools were employed to analyze the spatiotemporal urban landuse changes. Object-Based Image Analysis (OBIA), Landuse Cover Change (LUCC) analysis and urban sprawl analysis using Shannon Entropy were carried out. The Land Change Modeler (LCM) was used to develop a model of urban growth. The Multi-layer Perceptron Neural Network was employed to model the transition potential maps with an accuracy of 85.9% and these were used as an input for the ‘actual’ urban modeling with Markov chains. Model validation was assessed and a scenario of urban land use change of the GAA up to year 2020 was presented. The result of the study indicated that the built-up area has tripled in size (increased by 4,441 ha) between 1989 and 2009. Specially, after year 2000 urban sprawl in GAA caused large scale encroachment on high potential agricultural lands and plantation cover. The scenario for year 2020 shows an increase of the built-up areas by 1,484 ha (25%) which may cause further loss. The study indicated that the land allocation system in the GAA overrode the landuse plan, which caused the loss of agricultural land and plantation cover. The recommended policy options might support decision makers to resolve further loss of agricultural land and plantation cover and to achieve sustainable urban development planning in the GAA.

Monitoring Urban Sprawl Using Remote Sensing and GIS Techniques of a Fast Growing Urban Centre, India

Abstract: India's urban population has grown tremendously in the last four decades from 79 million in 1961 to 285 million in 2001. This fast rate of increase in urban population is mainly due to large scale migration of people from rural and smaller towns to bigger cities in search of better employment opportunities and good life style. This rapid population pressure has resulted in unplanned growth in the urban areas to accommodate these migrant people which in turn leads to urban sprawl. It is a growing problematic aspect of metropolitan and bigger city's growth and development in recent years in India. Urban sprawl has resulted in loss of productive agricultural lands, open green spaces, loss of surface water bodies and depletion of ground water. Therefore, there is a need to study, understand and quantify the urban sprawl. In this paper an attempt has been made to use Shannon's entropy model to assess urban sprawl using IRS P-6 data and topographic sheet in GIS environment for one of the fastest growing city of South India and its surrounding area. The built-up area of the city has increased from 135 km2 in 1971 to 370 km2 in 2005. The study shows that there is a remarkable urban sprawl in and around the twin city between 1971 and 2005 because 215 km2 of agricultural land has lost to built-up land during this period. As a result the urban ecosystem has changed in the last four decades.

Nature of vegetation and building morphology characteristics across a city: Influence on shadow patterns and mean radiant temperatures in London

Abstract: Vegetation and building morphology characteristics are investigated at 19 sites on a north-south LiDAR transect across the megacity of London. Local maxima of mean building height and building plan area density at the city centre are evident. Surprisingly, the mean vegetation height (zv3) is also found to be highest in the city centre. From the LiDAR data various morphological parameters are derived as well as shadow patterns. Continuous images of the effects of buildings and of buildings plus vegetationon sky view factor (Ψ) are derived. A general reduction of Ψ is found, indicating the importance of including vegetation when deriving Ψ in urban areas. The contribution of vegetation to the shadowing at ground level is higher during summer than in autumn. Using these 3D data the influence on urban climate and mean radiant temperature (T mrt ) is calculated with SOLWEIG. The results from these simulations highlight that vegetation can be most effective at reducing heat stress within dense urban environments in summer. The daytime average T mrt is found to be lowest in the densest urban environments due to shadowing; foremost from buildings but also from trees. It is clearly shown that this method could be used to quantify the influence of vegetation on T mrt within the urban environment. The results presented in this paper highlight a number of possible climate sensitive planning practices for urban areas at the local scale (i.e. 102- 5 × 103 m).