Showing papers on "Urban climate published in 2007"

Adapting cities for climate change: the role of the green infrastructure.

Abstract: The urban environment has distinctive biophysical features in relation to surrounding rural areas. These include an altered energy exchange creating an urban heat island, and changes to hydrology such as increased surface runoff of rainwater. Such changes are, in part, a result of the altered surface cover of the urban area. For example less vegetated surfaces lead to a decrease in evaporative cooling, whilst an increase in surface sealing results in increased surface runoff. Climate change will amplify these distinctive features. This paper explores the important role that the green infrastructure, i.e. the greenspace network, of a city can play in adapting for climate change. It uses the conurbation of Greater Manchester as a case study site. The paper presents output from energy exchange and hydrological models showing surface temperature and surface runoff in relation to the green infrastructure under current and future climate scenarios. The implications for an adaptation strategy to climate change in the urban environment are discussed.

Understanding the Benefits and Costs of Urban Forest Ecosystems

Abstract: One of the first considerations in developing a strong and comprehensive urban forestry program is determining the desired outcomes from managing and maintaining vegetation in cities. Urban trees offer a wide range of potential benefits to the urban environment and society. However, there also are a wide range of potential costs and, as with all ecosystems, numerous interactions that must be understood if society is to optimize the net benefits from urban vegetation. Inadequate understanding of the wide range of benefits, costs, and expected outcomes of urban vegetation management designs and plans, as well as interactions among them, may drastically reduce the contribution of vegetation toward improving urban life and the environment.

Living in the city: can anyone become an ‘urban exploiter'?

Abstract: Aim As urban landscapes expand, shifts in biodiversity are occurring. This is leading biogeographers and ecologists to consider human-dominated landscapes in their current work. One question that arises is: what characterizes those species that are widespread in the most highly urban environments compared with those restricted to less urbanized areas in the city? Here, we aim to identify the traits that enable species to become urban exploiters, i.e. to dominate highly urbanized surroundings. Identifying these traits may help us better predict and possibly mitigate the biotic homogenization occurring in these areas.

ARTICLE Living in the city: can anyone become an 'urban exploiter'?

Abstract: Aim As urban landscapes expand, shifts in biodiversity are occurring. This is leading biogeographers and ecologists to consider human-dominated landscapes in their current work. One question that arises is: what characterizes those species that are widespread in the most highly urban environments compared with those restricted to less urbanized areas in the city? Here, we aim to identify the traits that enable species to become urban exploiters, i.e. to dominate highly urbanized surroundings. Identifying these traits may help us better predict and possibly mitigate the biotic homogenization occurring in these areas. Location Israel in general, with special focus on the city of Jerusalem. Methods Combining literature and field-based data for birds in Israel we compared phenotypic, behavioural and life-history traits between urban exploiters and urban adapters. The latter occur in urban landscapes, but are characteristic of the less urbanized parts of the city. We then examined the trends along a finer field-sampled gradient of increasing urbanization from sub-natural to downtown areas within the city of Jerusalem. Results Urban exploiters and adapters differed primarily in social structure and migratory status: exploiters were significantly more social and sedentary than urban adapters. Clear trends were also seen for dietary preferences along a gradient of increasing urbanization in Jerusalem, such that, with increasing urbanization, the proportion of granivorous species increased whereas the proportion of species feeding on invertebrates declined. In contrast, neither relative brain size nor behavioural flexibility, as measured by feeding innovations, differed significantly among urban exploiters and adapters in Israel or along the urbanization gradient in Jerusalem specifically. Main conclusions The results of our study suggest that being successful in more vs. less urbanized environments in the city is not necessarily a factor of brain size nor of how flexible and behaviourally innovative the species is; rather, it depends on a combination of traits, including diet, degree of sociality, sedentariness and preferred nesting sites.

Review of urban climate research in (sub)tropical regions

Abstract: Over the last 50 years the developing world, much of which is located in (sub)tropical regions, has seen a dramatic growth of its urban population associated with serious degradation of environmental quality. The total number of (sub)tropical urban climate studies, however; is still small (<20% of all urban climate studies). The available work is further biased towards descriptive studies rather than process work that seeks to indicate the physical climatology of (sub)tropical cities. The available results allow for a preliminary comparison with data from temperate latitudes. Urban heat island (UHI) intensities are generally lower compared to those of temperate cities with comparable population and show a seasonal variation with lower (higher) intensities during the wet (dry) season. (Sub)tropical population-based relations may exist but insufficient appropriate data is available to confirm a logarithmic relationship or systematic differences between different climate types. The (sub)tropical energy balance studies are biased towards dry, clear sky conditions. The amount of net radiation dissipated by sensible heat during daytime is about 40% which is similar to values observed in (sub)urban areas of cities located in temperate climates. Energy partitioning is modulated by water availability and higher percentage of vegetation promotes latent heat flux at the expense of surface heat storage. The apparent strong influence of vegetation and water availability on the energy partitioning irrespective of the climate type, suggests vegetation to be an effective means to reduce heat storage uptake during daytime and hence has the potential to effectively mitigate the nocturnal heat island. It is important to ensure that the rapidly expanding cities of the developing world incorporate climatological concerns in their design to provide a better living and working environment for a large segment of the world's inhabitants. Copyright © 2007 Royal Meteorological Society

Climate Response to Rapid Urban Growth: Evidence of a Human-Induced Precipitation Deficit

Abstract: The authors establish the effect of urbanization on precipitation in the Pearl River Delta of China with data from an annual land use map (1988–96) derived from Landsat images and monthly climate data from 16 local meteorological stations. A statistical analysis of the relationship between climate and urban land use in concentric buffers around the stations indicates that there is a causal relationship from temporal and spatial patterns of urbanization to temporal and spatial patterns of precipitation during the dry season. Results suggest an urban precipitation deficit in which urbanization reduces local precipitation. This reduction may be caused by changes in surface hydrology that extend beyond the urban heat island effect and energy-related aerosol emissions.

Impact of Increasing Urban Density on Local Climate: Spatial and Temporal Variations in the Surface Energy Balance in Melbourne, Australia

Abstract: Variations in urban surface characteristics are known to alter the local climate through modification of land surface processes that influence the surface energy balance and boundary layer and lead to distinct urban climates. In Melbourne, Australia, urban densities are planned to increase under a new strategic urban plan. Using the eddy covariance technique, this study aimed to determine the impact of increasing housing density on the surface energy balance and to investigate the relationship to Melbourne’s local climate. Across four sites of increasing housing density and varying land surface characteristics (three urban and one rural), it was found that the partitioning of available energy was similar at all three urban sites. Bowen ratios were consistently greater than 1 throughout the year at the urban sites (often as high as 5) and were higher than the rural site (less than 1) because of reduced evapotranspiration. The greatest difference among sites was seen in urban heat storage, which was influenced by urban canopy complexity, albedo, and thermal admittance. Resulting daily surface temperatures were therefore different among the urban sites, yet differences in above-canopy daytime air temperatures were small because of similar energy partitioning and efficient mixing. However, greater nocturnal temperatures were observed with increasing density as a result of variations in heat storage release that are in part due to urban canyon morphology. Knowledge of the surface energy balance is imperative for urban planning schemes because there is a possibility for manipulation of land surface characteristics for improved urban climates.

Climate Change and Developing-Country Cities: Implications For Environmental Health and Equity

Abstract: Climate change is an emerging threat to global public health. It is also highly inequitable, as the greatest risks are to the poorest populations, who have contributed least to greenhouse gas (GHG) emissions. The rapid economic development and the concurrent urbanization of poorer countries mean that developing-country cities will be both vulnerable to health hazards from climate change and, simultaneously, an increasing contributor to the problem. We review the specific health vulnerabilities of urban populations in developing countries and highlight the range of large direct health effects of energy policies that are concentrated in urban areas. Common vulnerability factors include coastal location, exposure to the urban heat-island effect, high levels of outdoor and indoor air pollution, high population density, and poor sanitation. There are clear opportunities for simultaneously improving health and cutting GHG emissions most obviously through policies related to transport systems, urban planning, building regulations and household energy supply. These influence some of the largest current global health burdens, including approximately 800,000 annual deaths from ambient urban air pollution, 1.2 million from road-traffic accidents, 1.9 million from physical inactivity, and 1.5 million per year from indoor air pollution. GHG emissions and health protection in developing-country cities are likely to become increasingly prominent in policy development. There is a need for a more active input from the health sector to ensure that development and health policies contribute to a preventive approach to local and global environmental sustainability, urban population health, and health equity.

Urban Heat Islands: Observations, Impacts, and Adaptation

Abstract: Urban heat islands are a clear, well-documented example of an anthropogenic modification to climate that has an atmospheric, biological, and economic impact. This review shows how field-based and modeling studies continue to help unravel the factors that are responsible for heat island development and are providing a basis for the development and application of sustainable adaptation strategies. As urban areas continue to expand, there is a heightened awareness that scientific knowledge of the urban heat island must be more effectively communicated to architects, engineers, and planners and translated into intelligent urban design. Green roof technology is a case in point. This and other technologies are being slowly adopted, and research published since 2003 suggests that the pace with which many practical applications are put into practice should accelerate.

Urban heat islands in humid and arid climates: role of urban form and thermal properties in Colombo, Sri Lanka and Phoenix, USA

Abstract: Using a micro-scale urban simulation program, we examined the sensitivity of air tem- perature and mean radiant temperature (MRT) of built-up urban cores to urban-area geometry (the density of buildings), thermal properties of human-made surfaces (albedo) and green cover (street trees), in 2 warm-climate cities: Pettah, Colombo (Sri Lanka) and downtown Phoenix, Arizona (USA). Air temperature and MRT are indicative of human thermal comfort, and their rural/urban gradients signify the urban heat island (UHI) effect. Although high albedo values lead to low daytime temper- atures in both cities, the best thermal comfort, quantified by both the air temperature and MRT, was found in high-density development. Thus, density enhancement is a viable UHI mitigation option in built-up areas of warm climate cities. Manipulation of thermal properties is an alternative strategy, but the practical utility of high albedo surfaces is questionable. Additionally, some UHI mitigation options are more likely to bring improvements in MRT than in air temperature. Urban designers should use mitigation options that are based on human comfort, which is determined by both MRT and air temperature, rather than simply attempting to control air temperature alone.

Thermal comfort in an east–west oriented street canyon in Freiburg (Germany) under hot summer conditions

Abstract: Field-measurements were conducted in an urban street canyon with an east–west orientation, and a height-to-width ratio H/W = 1 during cloudless summer weather in 2003 in Freiburg, Germany. This experimental work adds to the knowledge available on the microclimate of an urban canyon and its impact on human comfort. Air temperature T a , air humidity VP, wind speed v and direction dd were measured continuously. All short-wave and long-wave radiation fluxes from the 3D surroundings were also measured. The degree of comfort was defined in terms of physiologically equivalent temperature (PET). Furthermore, the data gathered within the canyon were compared to data collected by a permanent urban climate station with the aim of furthering the understanding of microclimatic changes due to street geometry. Changes in the meteorological variables T a , v and dd in the canyon in comparison to an unobstructed roof level location were found to be in good agreement with previous studies, i.e., a small increase of T a in the canyon adjacent to irradiated surfaces, and a good correlation of v and dd between canyon and roof levels. The daily dynamics of canyon facet irradiances and their impacts on the heat gained by a pedestrian were strongly dependent on street geometry and orientation. Thermal stress was mostly attributable to solar exposure. Under cloudless summer weather, a standing body was found to absorb, on average, 74% of heat in the form of long-wave irradiance and 26% as short-wave irradiance. Shading the pedestrian as well as the surrounding surfaces is, hence, the first strategy in mitigating heat stress in summer under hot conditions.

Riding the Wave of Urban Growth in the Countryside: Spread, Backwash, or Stagnation?

Abstract: The advisability of an urban-centered growth strategy to reap the benefits of urban agglomeration economies is much debated. Rural areas benefit when the growth "spreads" to the hinterlands, especially within daily commuting distance. Yet, in distant-peripheral locations, urban growth may create a "backwash" as households relocate to the urban center. This study examines spread vs. backwash, as separate from long-run, distance-from-urban-center trend effects, using a novel Canadian GIS database. The unique nation-wide approach yields a spread and backwash rural-growth topography that varies by distance from the urban center, by urban population vs. income growth, and by size of rural community.

Urban and rural temperature trends in proximity to large US cities: 1951–2000

Abstract: This paper presents a study of urban and rural temperature trends in proximity to the most populous metropolitan areas of the US. As data from urban meteorological stations are typically eliminated or adjusted for use in continental and global analyses of climate change, few studies have addressed how temperatures are changing in the areas most vulnerable to the public health impacts of warming: large cities. In this study, temperature data from urban and proximate rural stations for 50 large US metropolitan areas are analysed to establish the mean decadal rate of change in urban temperatures, rural temperatures, and heat island intensity over five decades. The results of this analysis find the mean decadal rate of change in the heat island intensity of large US cities between 1951 and 2000 to be 0.05 °C and further show a clear division in temperature trends between cities situated in the northeastern and southern regions of the country. Copyright © 2007 Royal Meteorological Society

Increased Temperature and Intensification of the Urban Heat Island: Implications for Human Comfort and Urban Design

Abstract: The predicted rise in air temperatures due to climate change is exacerbated in urban areas by the heat island effect, which is also predicted to increase. The combined effect, in a temperate climate, will have some benefits in the cooler seasons but in the summertime will increase heat stress and the energy used for cooling. This paper refers to research results showing how changes to urban design can improve thermal comfort. It also shows how changing the albedo of the surfaces of the buildings can reduce the impact of solar radiation by reducing the radiant temperature of the environment. The benefits of increased vegetation within the urban environment are shown from measurements in the context of the urban London environment.

Spatio-temporal analysis for monitoring urban growth – a case study of Indore City

Abstract: Urban sprawl is characterized by haphazard patchwork of development, which leads to an improper development in any city. To prevent this kind of sprawl in future, it is necessary to monitor the growth of the city. Hence, an attempt has been made in the present study to monitor the urban growth over a period of time by employing Remote Sensing and Geographic Information System techniques in conjunction with Shannon entropy. Shannon entropy is a measure to determine the compactness or dispersion of built-up land growth in the urban areas. The growth patterns of urban built-up land have been studied initially by dividing the area into four zones. The observations have been made with respect to each zone. Then, the study area has been divided into concentric circles of 1 km buffers and the growth patterns have been studied based on urban built-up density with respect to each circular buffer in all four zones. These observations have been integrated with road network to check the influence of infrastructure on haphazard urban growth. It has been found from the study that Shannon entropy is a good measure to determine the spatial concentration or dispersion of built-up land in the city. The study also proved the potential of RS and GIS techniques in the spatio-temporal analysis of urban growth trends and their consequences in the lands adjoining to urban areas.

Urban/rural atmospheric water vapour pressure differences and urban moisture excess in Krefeld, Germany

Abstract: Urban/rural humidity differences were analysed by means of a climate station pair in Krefeld (51° 20′N, 6° 33′E), Germany, during the period from 11/2001 to 10/2002, on the basis of hourly averages of water vapour pressure. Focus was put upon on the examination of frequency, timing and duration of the Urban Moisture Excess (UME) (Δeu−r > 0 hPa). It was found that the urban site was more humid (0 hPa 0.5 hPa; intense UME) in 4.6%. Weak and intense UME occur during every month of the year with different frequencies per month. A diurnal course of UME was found for summer but not for winter. Weak and intense UME events show frequency maxima in the second half of the night. Most of them are characterized by durations of 1 hour, in few cases several hours duration were observed for weak (up to 14 h) and intense UME (up to 12 h). The main reason for formation of UME events might be that the surface dew point at the rural station was reached more often, earlier and lasted longer in comparison to the urban environment. Copyright © 2007 Royal Meteorological Society

Effects of Urban Land-Use Change on Biogeochemical Cycles

Abstract: Urban land-use change, the conversion of agricultural recand natural ecosystems to human settlements, has become an important component of global change. Virtually all of the projected increase in the world's population is expected to occur in cities so that by the year 2007 more than half of the global population is expected to live in urban areas (United Nations 2004). Yet, urban settlements and surrounding areas are complex ecological systems that have only recently been studied from a rigorous ecological perspective (Pickett et al. 2001).

Urban—rural humidity differences in London

Abstract: Measurements of vapour pressure taken four times daily over a 10-year period are used to investigate diurnal and seasonal patterns of urban—rural absolute humidity differences in London. The urban atmosphere is found to be more humid than the rural at night in all months and during the day in winter and spring, while during summer days, the urban atmosphere is less humid. Patterns of urban excesses and deficits of humidity can be explained by reference to urban and rural energy balances and sources of moisture. A good relationship exists between heat island intensity and urban—rural vapour pressure differences.

The urban heat island Mitigation Impact Screening Tool (MIST)

Abstract: A web-based software tool has been developed to assist urban planners and air quality management officials in assessing the potential of urban heat island mitigation strategies to affect the urban climate, air quality, and energy consumption within their cities. The user of the tool can select from over 170 US cities for which to conduct the analysis, and can specify city-wide changes in surface reflectivity and/or vegetative cover. The Mitigation Impact Screening Tool (MIST) then extrapolates results from a suite of simulations for 20 cities to estimate air temperature changes associated with the specified changes in surface characteristics for the selected city. Alternatively the user can simply define a nominal air temperature reduction that they hope to achieve with an unspecified mitigation scenario. These air temperature changes are then input to energy and ozone models to estimate the impact that the mitigation action may have on the selected city. The results presented by MIST include a high degree of uncertainty and are intended only as a first-order estimate that urban planners can use to assess the viability of heat island mitigation strategies for their cities. As appropriate, MIST analyses should be supplemented by more detailed modeling.

Urbanization process and the changing agricultural landscape pattern in the urban fringe of Metro Manila, Philippines

Abstract: This paper discusses physical changes in the urban fringe agricultural landscape of Metro Manila and the socioeconomic factors and other pressures underlying these changes. In 1982, agricultural land use dominated in both of the two study areas, but the area under cultivation had decreased by 1997. The changing pattern in the northwest study area was one of phased transition towards a more urban land use. In contrast, in the southeast study area, there was a sudden change from an agricultural to an urban landscape. The paper explores the reasons for this difference and recommends the conservation of green open spaces through the adoption of an ecological planning approach involving a mixture of urban and agricultural land uses.

Lost in Space: Population Dynamics in the American Hinterlands and Small Cities

Abstract: The sources of urban agglomeration and the urban hierarchy have been extensively studied. Despite the pivotal role of the hinterlands in theories of the development of the urban hierarchy, little attention has been paid to the effect of urban agglomeration on growth in the hinterlands, particularly in a developed, mature economy. Therefore, this study examines how proximity to urban agglomeration affects contemporary population growth in hinterland U.S. counties. Proximity to urban agglomeration is measured in terms of both distances to higher-tiered areas in the urban hierarchy and proximity to market potential. Particular attention is paid to whether periodic changes and trends in underlying conditions (e.g., technology or transport costs) have altered population dynamics in the hinterlands and small urban centers. Over the period 1950-2000, we find strong negative growth effects of distances to higher-tiered urban areas, with significant, but lesser, effects of distance to market potential. Further, the costs of distance, if anything, appear to be increasing over time, consistent with various recent theories stressing the importance of how new technology affects the spatial distribution of activity in a mature urban system, while factors associated with the New Economic Geography are of lesser importance.

Changes in the nature of urban spatial structure in the united states, 1890–2000*

Abstract: This paper documents the long-run trends in the average densities and density gradients of urban areas in the United States. The data show that between 1890 and 2000 the average densities of cities and metropolitan areas rose and fell but that the density gradients of urban areas generally declined monotonically over time. While it is beyond the scope of this paper to estimate the causes of these changes, this paper argues that a complete understanding of the changes in the nature of US urban spatial structures is likely to go beyond the standard explanations based on the monocentric city model such as decreases in transportation costs and increases in household incomes.

Modelling the ground heat flux of an urban area using remote sensing data

Abstract: During the Basel Urban Boundary Layer Experiment (BUBBLE) conducted in 2002, micrometeorological in-situ data were collected for different sites using a variety of instruments. This provides a unique data set for urban climate studies. Nevertheless, the spatial distribution of energy and heat fluxes can only be taken into account with remote sensing methods or numerical models. Therefore, multiple satellite images from different platforms (NOAA-AVHRR, MODIS and LANDSAT ETM+) were acquired, processed and analysed. In addition, a high resolution digital elevation model (DEM) and a 1 m resolution digital surface model (DSM) of a large part of the city of Basel was utilized. This paper focuses on the calculation and modelling of the ground (or storage) heat flux density using remotely sensed data combined with in-situ measurements using three different approaches. First, an empirical regression function was generated to estimate the storage heat flux from NDVI values second approach used the Objective Hysteresis Model (OHM) which is often used for in-situ measurements. The last method used information of the geometric parameters of urban street canyons, computed from the high resolution digital urban surface model.

Cities and Nature

Abstract: Section 1: The Urban Environment in History 1 The City and Nature 2 Environmental Issues in Cities: A Brief History 3 The Industrial City 4 Contemporary Urbanisation and Environmental Dynamics Section 2: Urban Environmental Issues 5 Urban Sites 6 Cities, Environmental Hazards and Disasters 7 Urban Ecology 8 Water Pollution and the City 9 Air Pollution and the City 10 Garbage in the City Section 3: Realigning Urban-Nature Relations 11 Race, Class and Environmental Justice 12 Sustainable Urban Development

Modelling the urban climate using a local governmental geo-database

Abstract: In this study, local government digital spatial data are used to describe urban geometry and analyse spatial variations of the urban climate within the central areas of Goteborg, Sweden. A high-resolution raster digital elevation model (1 m pixel resolution) consisting of building structures and ground heights is derived from a local government geo-database, as well as land use patterns and artificial heat sources. Parameters such as the sky view factor (SVF) and daily averages of solar radiation are calculated. Results obtained from the model are compared with intra-urban air temperature variations which are derived from mobile measurements, as well as surface temperature variations derived from thermal infrared images. Results show that high-resolution digital elevation models in raster format are very useful sources of data for the investigation of intra-urban temperature variations. Results also show that the areal mean of SVF correlates with intra-urban air temperature variations to a higher degree than SVF that is taken from a point source location. The correlation between the modelled SVF and surface temperature is high during both spring and winter. Adding information about daily averages of global radiation for the spring measurement causes the correlation between SVF and surface temperature variations to increase. Copyright © 2007 Royal Meteorological Society