Showing papers on "Urban climate published in 2006"

Urban ecosystems and the North American carbon cycle

Abstract: Approximately 75–80% of the population of North America currently lives in urban areas as defined by national census bureaus, and urbanization is continuing to increase. Future trajectories of fossil fuel emissions are associated with a high degree of uncertainty; however, if the activities of urban residents and the rate of urban land conversion can be captured in urban systems models, plausible emissions scenarios from major cities may be generated. Integrated land use and transportation models that simulate energy use and traffic-related emissions are already in place in many North American cities. To these can be added a growing dataset of carbon gains and losses in vegetation and soils following urbanization, and a number of methods of validating urban carbon balance modeling, including top down atmospheric monitoring and urban ‘metabolic’ studies of whole ecosystem mass and energy flow. Here, we review the state of our understanding of urban areas as whole ecosystems with regard to carbon balance, including both drivers of fossil fuel emissions and carbon cycling in urban plants and soils. Interdisciplinary, whole-ecosystem studies of the socioeconomic and biophysical factors that influence urban carbon cycles in a range of cities may greatly contribute to improving scenarios of future carbon balance at both continental and global scales.

Towards better scientific communication in urban climate

Abstract: Better communication both within the field of urban climate and between urban climate and cognate fields is necessary to both bind the subject internally and to more effectively move it into interdisciplinary interaction. A brief statement of the wide diversity of the field and its several modes of study and application leads to the view that it would be beneficial to consider adopting aids to increase dialogue. This includes standardization of symbols, terminology and indices, classification of phenomena, a protocol to generalize site description, adoption of principles of experimental design and the use of dimensional analysis and normalization to aid the transferability of results. The focus of this paper is how to facilitate scientific interaction between participants within the field of urban climate, including both those who study its mechanisms and effects and those who apply such knowledge to the improvement of human settlements. As a by-product it may also assist communication between urban climatologists and workers in cognate fields as well as those we wish to entrain in the fields of policy development and environmental management. Section 1 explains the nature of the urban climate field and its practitioners, especially the diversity of scholarly disciplines, the range of topics studied and the motivations for doing so. Section 2 describes the sequence of investigative modes associated with achieving coherent understanding and intelligent application of urban climate. Section 3 attempts to outline some essential elements which might promote discourse between these modes such as the use of a common set of symbols and terminology and ways of expressing results so as to standardize variables and thereby assist comparison and transferability of results.

Ecological consequences of rapid urban expansion: Shanghai, China

Abstract: Since China's economic reform in the late 1970s, Shanghai, the country's largest and most modern city, has experienced rapid expansion and urbanization. Here, we explore its land‐use and land‐cover changes, focusing on the impacts of the urbanization process on air and water quality, local climate, and biodiversity. Over the past 30 years, Shanghai's urban area and green land (eg urban parks, street trees, lawns) have increased dramatically, at the expense of cropland. Concentrations of major air pollutants (eg SO₂, NOₓ, and total suspended particles) were higher in urban areas than in suburban and rural areas. Overall, however, concentrations have decreased (with the exception of NOₓ), due primarily to a decline in coal consumption by industry and in private households. Increased NOₓ pollution was mainly attributed to the huge increase in the number of vehicles on the roads. Water quality changes showed a pattern similar to that of air quality, with the most severe pollution occurring in urban areas. Differences in mean air temperatures between urban and rural areas also increased, in line with the rapid pace of urban expansion, indicating an accelerating “urban heat island” effect. Urban expansion also led to a decrease in native plant species. Despite its severe environmental problems, Shanghai has also seen major economic development. Managing the tradeoffs between urbanization and environmental protection will be a major challenge for Chinese policy makers. [Formula: see text]

Progress in measuring and observing the urban atmosphere

Abstract: Observations of atmospheric conditions and processes in cities provide the cornerstone for advances in the understanding of urban climates and are crucial to improving the performance of urban atmospheric models. Here, recent progress in the observation and measurement of the urban atmosphere is considered in terms of: first, the research directions of those involved in conducting urban climate observations; second, advances in technology, both direct in terms of the development of new sensors and indirect in terms of computing power and capabilities in data analysis; and third, enhanced understanding of sensor placement. Increasingly, urban based observational programs are collaborative, multi-institutional, multi-national, interdisciplinary initiatives. This has important implications for the research questions addressed and the potential to investigate processes and effects across multiple spatial and temporal scales. Advances in technology have provided urban climatologists with new, improved and often more affordable instrumentation, and the ability to process and analyze data more rapidly. Greater understanding of urban atmospheric processes, and atmospheric sciences more broadly, have resulted in important insights into appropriate placement of meteorological instruments and the interpretation of results. An important issue that the urban climate community must address is how best to archive data so it is not lost. A database of current and past studies with key metadata about sites, instrumentation and data processing is proposed. Well documented and available urban data sets will enable future researchers to continue to extract valuable new insights and verify existing understanding about urban atmospheric processes. Urban field studies can be costly and time-consuming, so continuing to exploit the rich, significantly untapped, historical data sets will allow steady progress in urban atmospheric research to continue, provided funding are available for analysis of the data.

Applied climatology: urban climate

Abstract: © 2006 Edward Arnold (Publishers) Ltd 10.1191/0309133306pp484pr

How urban structure can affect city sustainability from an air quality perspective

Abstract: Despite the progress made in controlling local air pollution, urban areas show increasing signs of environmental stress and air quality is one of the major concerns. The findings of several studies provide evidence that the shape of a city and the land use distribution determine the location of emission sources and the pattern of urban traffic, affecting urban air quality. This work focuses on the potential impacts of different land use patterns on urban air quality. Three imaginary cities were created, based on alternative urban planning strategies, considering different land use patterns: from the scenario of urban sprawl to the opposite scenario of a compact city with mixed land use. The mesoscale photochemical system MEMO/MARS was applied to evaluate the urban air quality in each of the idealized city structures. Simulation results indicate that more compact cities with mixed land use provide better urban air quality compared to disperse and network cities.

Climate change, biodiversity and the urban environment: a critical review based on London, UK:

Abstract: According to projections by the United Nations, 60% of the world’s population will reside in urban areas by 2030. Studies of the ecology of cities and ecology in cities will therefore assume increa...

The impact of urban areas on weather

Abstract: The industrial revolution led to a rapid development of urban areas. This has continued unremittingly over the last 200 years or so. In most urban areas the surface properties are heterogeneous, which has significant implications for energy budgets, water budgets and weather phenomena within the part of the earth's atmosphere that humans live. In this paper I discuss the structure of the planetary boundary layer, confining our analysis to the region above the rooftops (canopy layer) up to around the level where clouds form. It is in this part of the atmosphere that most of the weather impacting our lives occurs, and where the buildings of our cities impact the weather. In this review, observations of the structure of the urban atmospheric boundary layer are discussed. In particular the use of Doppler lidar provides measurements above the canopy layer. The impact of high-rise buildings is considered. Urban morphology impacts energy fluxes and airflow leading to phenomena such as the urban heat island and convective rainfall initiation. I discuss in situ surface-based remote sensing and satellite measurements of these effects. Measurements have been used with simple and complex numerical models to understand the complexity and balance of the interactions involved. Cities have been found to be sometimes up to 10 degC warmer than the surrounding rural areas, and to cause large increases in rainfall amounts. However, there are situations in which urban aerosol may suppress precipitation. Although much progress has been made in understanding these impacts, our knowledge remains incomplete. These limitations are identified. As city living becomes even more the norm for large numbers of people, it is imperative that we ensure that urban effects on the weather are included in development plans for the built environment of the future. Copyright © 2006 Royal Meteorological Society

Green Urban Political Ecologies: Toward a Better Understanding of Inner-City Environmental Change:

Abstract: This research uses a Marxist urban political ecology framework to link processes of urban environmental metabolization explicitly to the consumption fund of the built environment. Instead of reinventing the wheel, I argue in this paper that Marxist notions of metabolism are ideal for investigating urban environmental change and the production of uneven urban environments. In so doing, I argue that despite the embeddedness of Harvey's circuits of capital within urban political economy, these connected notions still have a great deal to offer regarding better understanding relations between consumption and metabolization of urban environments. From this theoretical perspective, I investigate urban socionatural metabolization as a function of the broader socioeconomic processes related to urban restructuring within the USA between 1962 and 1993 in the Indianapolis inner-city urban forest. The research examines the relations between changes in household income and changes in urban forest canopy cover. The res...

Nocturnal urban heat island in Lisbon (Portugal): main features and modelling attempts

Abstract: In recent years, several studies have examined the Lisbon urban climate. A central conclusion is the existence of a nocturnal urban heat island (mean ΔTu−r = 2.5 °C). The aim of this paper is to summarise several attempts carried out in the last decade to interpolate nocturnal air temperatures across Lisbon, in order to be able to draw thermal maps as accurately as possible. This study refers only to clear nights. Stepwise multiple regression and a Geographic Information System were used to model the relation between air temperature and parameters related to land-use and topography. The different regression models (coefficients of determination between 0.68 and 0.92) show that canopy layer air temperature depends on sky-view factor, building height and percentage of built-up area, but also to a great extend on mesoclimatic geographic factors such as altitude, topography and distance from the Tagus River. Examples of four frequently encountered nocturnal air temperature patterns are presented, each corresponds to a different weather type. This method employed could prove useful in drawing climatic maps that may be of use in master plans of urban municipalities.

Progress toward sustainable settlements: a role for urban climatology

Abstract: Sustainable development can be defined as that which meets the needs of the current generation while leaving sufficient resources for the needs of future generations. A central objective is to decouple conventional resource use (and its corollary, waste generation) from economic development through technological innovation, improved efficiency and changes in individual practices. As the global population becomes urbanized and human activity is concentrated in urban areas, settlement planning is a key aspect of sustainability. The widespread inclusion of environmental objectives in urban plans at all scales provides an opportunity for the incorporation of urban climate knowledge into the planning process on a routine basis. Many of the stated objectives have both direct and indirect connections to climate. However, for this to happen, climate research and results must be linked more explicitly to the objectives of the sustainable settlement. In this paper, the relevance of sustainability to urban design and climate is discussed and the potential contribution of current urban climatology is assessed, identifying areas of special consideration for transfer to achieve sustainable urban planning and design.

Urban surface biophysical descriptors and land surface temperature variations

Abstract: In remote sensing studies of land surface temperatures (LST), thematic land-use and land-cover (LULC) data are frequently employed for simple correlation analyses between LULC types and their thermal signatures Development of quantitative surface descriptors could improve our capabilities for modeling urban thermal landscapes and advance urban climate research This study developed an analytical procedure based upon a spectral unmixing model for characterizing and quantifying the urban landscape in Indianapolis, Indiana A Landsat Enhanced Thematic Mapper Plus image of the study area, acquired on 22 June 2002, was spectrally unmixed into four fraction endmembers, namely, green vegetation, soil, high and low albedo Impervious surface was then computed from the high and low albedo images A hybrid classification procedure was developed to classify the fraction images into seven land-use and land-cover classes Next, pixel-based LST measurements were related to urban surface biophysical descriptors derived from spectral mixture analysis (SMA) Correlation analyses were conducted to investigate land-cover based relationships between LST and impervious surface and green vegetation fractions for an analysis of the causes of LST variations Results indicate that fraction images derived from SMA were effective for quantifying the urban morphology and for providing reliable measurements of biophysical variables such as vegetation abundance, soil, and impervious surface An examination of LST variations within census block groups and their relationships with the compositions of LULC types, biophysical descriptors, and other relevant spatial data shows that LST possessed a weaker relation with the LULC compositions than with other variables (including urban biophysical descriptors, remote sensing biophysical variables, GIS-based impervious surface variables, and population density) Further research should be directed to refine spectral mixture modeling The use of multi-temporal remote sensing data for urban time-space modeling and comparison of urban morphology in different geographical settings are also feasible

Progress in the scale modeling of urban climate: Review

Abstract: This paper describes progress made in the scale modeling of urban climate. The studies reviewed are mainly indoor and outdoor experiments that use an array of urban-like flow obstacles or roughness elements such as cubes, blocks, and cylinders. Except for several important and unique studies, the many experiments that use a single obstacle, or those that use an array of elements to create a vegetation-like roughness are excluded from this review. Topics considered include turbulent flow, scalar dispersion, local transfer coefficient, radiative transfer, and the surface energy balance. More than 40 relevant studies are cited, and both significant developments and remaining problems are described. The future application of scale models to obtain a comprehensive understanding of urban climate is also examined, with the focus mainly upon the possibility of outdoor experiments.

The Earthscan Reader in Rural-Urban Linkages

Abstract: Part 1: Introduction * Small Urban Centres and Large Villages: The Habitat For Much of the World's Low-Income Population * Part II: Rural Urban Linkages and Livelihood Transformations * Survival and Accumulation Strategies at the Rural Urban Interface in North-West Tanzania * Changing Rural Urban Linkages in Mali, Nigeria and Tanzania * Evolving Rural Urban Relations and Livelihoods in Southeast Asia * Part III: Policies that Address, Ignore or Misunderstand Rural Urban Linkages * Transitions in Sub-Saharan Africa: Agriculture, Urbanization and Income Growth * A Regional Network Strategy for Reciprocal Rural Urban Linkages: An Agenda for Policy Research with Reference to Indonesia * The Role of Small and Intermediate Urban Centres in Regional and Rural Development: Assumptions and Evidence * The Small Town and Urban Context in China * Part 4 Mobility and Migration Between Rural and Urban Areas * Environmental Perceptions, Social Class and Demographic Change in Mexico City: A Comparative Approach * Improved Livelihoods In Improved Watersheds in India: Can Migration Be Mitigated? * Taking Advantage of Rural Assets as a Coping Strategy for the Urban Poor: The Case of Rural Urban Interrelations in Botswana * Part IV: Beyond the City Boundaries: Peri-Urban Areas and Environmental Issues * Urban Agriculture in the Metropolitan Zone of Mexico City: Changes Over Time in Urban, Suburban and Peri-Urban Areas * The Politics of Urban Rural Relations: Land Use Conversion in the Philippines * Ecological Footprints and Appropriated Carrying Capacity: What Urban Economics Leaves Out * An Overview of Urban Environmental Burdens at Three Scales: Intra-Urban, Urban-Regional and Global *

Assessing impact of urbanization on river water quality in the Pearl River Delta Economic Zone, China.

Abstract: The Pearl River Delta Economic Zone is one of the most developed regions in China. It has been undergoing a rapid urbanization since the reformation and opening of China in 1978. This process plays a significant impact on the urban environment, particularly river water quality. The main goal of this present study is to assess the impact of urban activities especially urbanization on river water quality for the study area. Some Landsat TM images from 2000 were used to map the areas for different pollution levels of urban river sections for the study area. In addition, an improved equalized synthetic pollution index method was utilized to assess the field analytical results. The results indicate that there is a positive correlation between the rapidity of urbanization and the pollution levels of urban river water. Compared to the rural river water, urban river water was polluted more seriously. During the urban development process, urbanization and urban activities had a significant negative impact on the river water quality.

The surface energy balance and boundary layer over urban street canyons

Abstract: SUMMARY A model is developed for the energy balance of an urban area, represented as a sequence of two-dimensional street canyons. The model incorporates a novel formulation for the sensible-heat flux, that has previously been validated against wind tunnel models, and a formulation for radiation that includes multiple reflections and shadowing. This energy balance model is coupled to a model for the atmospheric boundary layer. Results are analysed to establish how the physical processes combine to produce the observed features of urban climate, and to establish the roles of building form and fabric on the urban modification to climate. Over a diurnal cycle there are morning and evening transition periods when the net flux of radiation is largely balanced by the flux of heat into the surface. The urban surface has a large surface area in contact with the air, and hence a large active heat capacity, and so the urban area needs to absorb a larger amount of heat than a rural area to change the surface temperature. The morning and evening transitions are therefore prolonged over urban areas, delaying the onset of convective or stable boundary layers after sunrise and sunset. The model shows that the energy balance of the roof behaves very differently from the combined energy balance of the street canyon system of walls and street. The sensible-heat flux from the street canyon into the boundary layer is increased by the increased surface area, but is decreased by the buildings reducing the local flow speeds. The net result is that, for the two-dimensional geometry investigated here, the sensible-heat flux from the canyon is not strongly sensitive to canyon geometry. The sensible-heat flux from the roof is larger than from the street, and so the total sensible-heat flux into the boundary layer, and hence also the air temperature, is strongly dependent on the fraction of plan area occupied by roofs. The radiation budget of the street canyon, which largely drives the temperatures of the canyon surfaces, is significantly changed by the limited sky view and multiple reflections caused by the local building form. The canyon surface temperatures thus depend strongly on local building morphology. Finally, two mechanisms are suggested for how urban areas might maintain a positive sensible-heat flux at night. Firstly, if the roof material has much lower heat capacity than the street canyon surfaces, then the roof can cool the boundary-layer air faster than the street canyon surfaces cool, leading to a positive heat flux out of the street canyon. Secondly, advection decouples the boundary layer from the local surface energy balance. In this way, cool air, perhaps from a rural area, advected on to an urban surface can lead to a positive sensible-heat flux which then tends to neutralize any stable stratification in the boundary layer.

Urban Land Use Change Analysis of a Traditional City from Remote Sensing Data: The Case of Ibadan Metropolitan Area, Nigeria

Abstract: Urban land uses had been increasingly subjected to changes of different forms, sorts and types since urban explosion of the 1970s. People move to cities en-mass from the rural hinterland to the cities in anticipations to benefit from urban economy. However most Nigerian cities are not planned and thus are not prepared fro the surge in urban explosion that resulted from the rural urban migration and the biological growth that made most Nigerian cities what they are today- a decadence of humanity. The changes in these residential land uses in urban area are subject of research discourse for a long time. This paper seeks to evaluate urban temporal changes in a typical traditional settlement in Nigeria-Ibadan. The techniques of remote sensing to evaluate land use land cover changes was employed and a projection into 2023 was done using marcov change model. The density classification and the change rate were utilized in correlation analysis to identify the relationship between the density types at the base year with the rate of change in the study area. It was observed that there are considerable dynamic changes in Ibadan metropolis and the major contributor to changes is the vegetal cover, low density and sprawl development. There are growths by fission within n even the high- density areas and the catchments area for rivers are also location for urban spatial growth or change. The paper concludes by suggesting ways to tame haphazard urban growth that characterizes Ibadan and major urban settlement in Nigeria.

Competition for the use of public open space in low-income urban areas: the economic potential of urban gardening in Khayelitsha, Cape Town

Abstract: Urban agriculture is a contested issue in the larger South African debate on urban poverty alleviation. This paper investigates the economic viability of urban agriculture and informs the debate on the optimal use of open space in Khayelitsha. It compares the economic performance of the Scaga community garden in the low-income township Khayelitsha, predicted in a 1998 study by Fermont et al., with empirical results of a similar study by Fleming in 2003. It concludes that urban agriculture in Khayelitsha is potentially economically viable, subject to certain conditions being satisfied. However, as a land use, urban agriculture competes with housing, ecological corridors, the stormwater management system and nature areas and reserves.