Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island
TL;DR: In this article, the authors reviewed progress in urban climatology over the two decades since the first publication of the International Journal of Climatology (IJC) and highlighted the role of scale, heterogeneity, dynamic source areas for turbulent fluxes and the complexity introduced by the roughness sublayer over the tall, rigid roughness elements of cities.
Abstract: Progress in urban climatology over the two decades since the first publication of the International Journal of Climatology is reviewed. It is emphasized that urban climatology during this period has benefited from conceptual advances made in microclimatology and boundary-layer climatology in general. The role of scale, heterogeneity, dynamic source areas for turbulent fluxes and the complexity introduced by the roughness sublayer over the tall, rigid roughness elements of cities is described. The diversity of urban heat islands, depending on the medium sensed and the sensing technique, is explained. The review focuses on two areas within urban climatology. First, it assesses advances in the study of selected urban climatic processes relating to urban atmospheric turbulence (including surface roughness) and exchange processes for energy and water, at scales of consideration ranging from individual facets of the urban environment, through streets and city blocks to neighbourhoods. Second, it explores the literature on the urban temperature field. The state of knowledge about urban heat islands around 1980 is described and work since then is assessed in terms of similarities to and contrasts with that situation. Finally, the main advances are summarized and recommendations for urban climate work in the future are made. Copyright © 2003 Royal Meteorological Society.
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TL;DR: A meta-analysis of 326 studies that have used remotely sensed images to map urban land conversion 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.
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.
1,712 citations
Cites background from "Two decades of urban climate resear..."
...Urban areas affect their local climate through the modification of surface albedo and evapotranspiration, and increased aerosols and anthropogenic heat sources, resulting in elevated temperatures [6] and changes in precipitation patterns [7,8]....
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TL;DR: Using MODIS data from 2003 to 2012, it is shown that the UHI effect decayed exponentially toward rural areas for majority of the 32 Chinese cities, and an obvious urban/rural temperature “cliff” is found.
Abstract: Urban heat island (UHI) is one major anthropogenic modification to the Earth system that transcends its physical boundary. Using MODIS data from 2003 to 2012, we showed that the UHI effect decayed exponentially toward rural areas for majority of the 32 Chinese cities. We found an obvious urban/rural temperature “cliff”, and estimated that the footprint of UHI effect (FP, including urban area) was 2.3 and 3.9 times of urban size for the day and night, respectively, with large spatiotemporal heterogeneities. We further revealed that ignoring the FP may underestimate the UHI intensity in most cases and even alter the direction of UHI estimates for few cities. Our results provide new insights to the characteristics of UHI effect and emphasize the necessity of considering city- and time-specific FP when assessing the urbanization effects on local climate.
1,523 citations
TL;DR: A review of the current status of selected remote sensing algorithms for estimating land surface temperature from thermal infrared (TIR) data is presented in this article, along with a survey of the algorithms employed for obtaining LST from space-based TIR measurements.
1,470 citations
Cites background or methods from "Two decades of urban climate resear..."
...As such, the LST is widely used in a variety of fields including evapotranspiration, climate change, hydrological cycle, vegetation monitoring, urban climate and environmental studies, among others (Arnfield, 2003; Bastiaanssen et al., 1998; Hansen et al., 2010; Kalma et al., 2008; Kogan, 2001; Su, 2002; Voogt & Oke, 2003;Weng, 2009;Weng et al., 2004) and has been recognized as one of the high-priority parameters of the International Geosphere and Biosphere Program (IGBP) (Townshend et al....
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...…including evapotranspiration, climate change, hydrological cycle, vegetation monitoring, urban climate and environmental studies, among others (Arnfield, 2003; Bastiaanssen et al., 1998; Hansen et al., 2010; Kalma et al., 2008; Kogan, 2001; Su, 2002; Voogt & Oke, 2003;Weng, 2009;Weng et al.,…...
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TL;DR: In this paper, a review of the literature available in this area includes the latest research approaches, concepts, methodologies, latest investigation tools and mitigation measures and concluded that the future research should be focused on design and planning parameters for reducing the effects of urban heat island and ultimately living in a better environment.
Abstract: Urban Heat Island (UHI) is considered as one of the major problems in the 21st century posed to human beings as a result of urbanization and industrialization of human civilization. The large amount of heat generated from urban structures, as they consume and re-radiate solar radiations, and from the anthropogenic heat sources are the main causes of UHI. The two heat sources increase the temperatures of an urban area as compared to its surroundings, which is known as Urban Heat Island Intensity (UHII). The problem is even worse in cities or metropolises with large population and extensive economic activities. The estimated three billion people living in the urban areas in the world are directly exposed to the problem, which will be increased significantly in the near future. Due to the severity of the problem, vast research effort has been dedicated and a wide range of literature is available for the subject. The literature available in this area includes the latest research approaches, concepts, methodologies, latest investigation tools and mitigation measures. This study was carried out to review and summarize this research area through an investigation of the most important feature of UHI. It was concluded that the heat re-radiated by the urban structures plays the most important role which should be investigated in details to study urban heating especially the UHI. It was also concluded that the future research should be focused on design and planning parameters for reducing the effects of urban heat island and ultimately living in a better environment.
1,160 citations
TL;DR: It is argued that, in addition to altered habitat structure, three major processes contribute to the patterns of reduced species diversity and elevated abundance of many species in urban environments.
Abstract: Rapid urbanization has become an area of crucial concern in conservation owing to the radical changes in habitat structure and loss of species engendered by urban and suburban development. Here, we draw on recent mechanistic ecological studies to argue that, in addition to altered habitat structure, three major processes contribute to the patterns of reduced species diversity and elevated abundance of many species in urban environments. These activities, in turn, lead to changes in animal behavior, morphology and genetics, as well as in selection pressures on animals and plants. Thus, the key to understanding urban patterns is to balance studying processes at the individual level with an integrated examination of environmental forces at the ecosystem scale.
1,046 citations
References
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TL;DR: It is shown that a satisfactory account can be given of open water evaporation at four widely spaced sites in America and Europe, the results for bare soil receive a reasonable check in India, and application of theresults for turf shows good agreement with estimates of evapolation from catchment areas in the British Isles.
Abstract: Two theoretical approaches to evaporation from saturated surfaces are outlined, the first being on an aerodynamic basis in which evaporation is regarded as due to turbulent transport of vapour by a process of eddy diffusion, and the second being on an energy basis in which evaporation is regarded as one of the ways of degrading incoming radiation. Neither approach is new, but a combination is suggested that eliminates the parameter measured with most difficulty—surface temperature—and provides for the first time an opportunity to make theoretical estimates of evaporation rates from standard meteorological data, estimates that can be retrospective. Experimental work to test these theories shows that the aerodynamic approach is not adequate and an empirical expression, previously obtained in America, is a better description of evaporation from open water. The energy balance is found to be quite successful. Evaporation rates from wet bare soil and from turf with an adequate supply of water are obtained as fractions of that from open water, the fraction for turf showing a seasonal change attributed to the annual cycle of length of daylight. Finally, the experimental results are applied to data published elsewhere and it is shown that a satisfactory account can be given of open water evaporation at four widely spaced sites in America and Europe, the results for bare soil receive a reasonable check in India, and application of the results for turf shows good agreement with estimates of evaporation from catchment areas in the British Isles.
6,711 citations
"Two decades of urban climate resear..." refers methods in this paper
...It adapts the well-established Penman–Monteith–Rutter–Shuttleworth evapotranspiration–interception model (Penman, 1948; Monteith, 1965; Rutter et al., 1971: Shuttleworth, 1978), originally developed for forests, to suburban use, and employs the Schmid and Oke (1990) source area model and the OHM…...
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TL;DR: In this article, the large-scale parameterization of the surface fluxes of sensible and latent heat is properly expressed in terms of energetic considerations over land while formulas of the bulk aerodynamic type are most suitahle over the sea.
Abstract: In an introductory review it is reemphasized that the large-scale parameterization of the surface fluxes of sensible and latent heat is properly expressed in terms of energetic considerations over land while formulas of the bulk aerodynamic type are most suitahle over the sea. A general framework is suggested. Data from a number of saturated land sites and open water sites in the absence of advection suggest a widely applicable formula for the relationship between sensible and latent heat fluxes. For drying land surfaces, we assume that the evaporation rate is given by the same formula for evaporation multiplied by a factor. This factor is found to remain at unity while an amount of water, varying from one site to another, is evaporated. Following this a linear decrease sets in, reducing the evaporation rate to zero after a further 5 cm of evaporation, the same at several sites examined.
5,918 citations
"Two decades of urban climate resear..." refers methods in this paper
...The scheme includes an evaporation model of the combination type (Priestley and Taylor, 1972) and performs calculations for suburban areas based on three distinct surface types: impervious, pervious irrigated and pervious unirrigated....
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Journal Article•
TL;DR: Progress towards a reconciliation of parallel concepts in meteorology and physiology is described, which stresses the importance of physiological restraint on the rate of transpiration from an irrigated field surrounded by dry land.
Abstract: A turgid leaf exposed to bright sunshine can transpire an amount of water several times its own weight during a summer day. Rapid evaporation is sustained by a supply of heat from the atmosphere and by a movement of water within the plant preventing the desiccation of leaf tissue. In analysis, the need for energy and the need for water have often been disassociated. Meteorologists investigating the energetics of transpiration have assumed that leaves behave like pieces of wet, green blotting paper, and plant physiologists have demonstrated mechanisms for the conduction of water at arbitrary rates unrelated to the physics of the environment. This paper describes progress towards a reconciliation of parallel concepts in meteorology and physiology. The path for the diffusion of water vapour from leaf cells to the free atmosphere is divided into two parts, one determined primarily by the size and distribution of stomata, and the other by wind speed and the aerodynamic properties of the plant surface. Diffusive resistances for single leaves and for plant communities are established from measurements in the laboratory and in the field and are then used: (i) to predict relative rates of evaporation from leaves with wet and dry surfaces; (ii) to investigate the dependence of transpiration rate on wind speed and surface roughness; (iii) to demonstrate that the relation between transpiration rate and lead area is governed by stomatal closure in leaves well shaded from sunlight; (iv) to calculate maximum rates of transpiration for different crops and climates. A final section on the convection of dry air stresses the importance of physiological restraint on the rate of transpiration from an irrigated field surrounded by dry land.
4,686 citations
"Two decades of urban climate resear..." refers methods in this paper
...It adapts the well-established Penman–Monteith–Rutter–Shuttleworth evapotranspiration–interception model (Penman, 1948; Monteith, 1965; Rutter et al., 1971: Shuttleworth, 1978), originally developed for forests, to suburban use, and employs the Schmid and Oke (1990) source area model and the OHM…...
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3,443 citations
"Two decades of urban climate resear..." refers background in this paper
...This migration is a positive aspect of the field’s recent history (Terjung, 1976; Oke, 1982), because it enhances the explanatory power urban climatologists have at their disposal....
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...At the beginning of the review period (Oke, 1979b, 1982), additional attenuation by urban boundarylayer pollutants was believed to reduce solar irradiance K↓ at the top of the UCL by 0–10% in general (but up to 20% in some cases: see Table 1 in Oke (1988b))....
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...Incoming longwave radiation L↓ is generally believed to be increased by urban areas, either due to the increased warmth of the urban atmosphere (UHI) or enhanced atmospheric emissivity brought about by the presence of particulate and gaseous pollutants (Oke, 1979b, 1982)....
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...Though the UHI studies published in the last 20 years have broadened the geographic scope of the phenomenon, the generalizations offered by Oke (1982) largely remain unchanged (Table III)....
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...Oke (1982) stated that urban heat islands were ‘well described but rather poorly understood’....
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TL;DR: In this article, the authors investigated the results of recent urban canyon field studies and of scale and mathematical modelling to find a range of canyon geometries that are compatible with the apparently conflicting design objectives of mid-latitude cities.
1,493 citations