Urban Climates
Abstract
Urban Climates is the first full synthesis of modern scientific and applied research on urban climates. The book begins with an outline of what constitutes an urban ecosystem. It develops a comprehensive terminology for the subject using scale and surface classification as key constructs. It explains the physical principles governing the creation of distinct urban climates, such as airflow around buildings, the heat island, precipitation modification and air pollution, and it then illustrates how this knowledge can be applied to moderate the undesirable consequences of urban development and help create more sustainable and resilient cities. With urban climate science now a fully-fledged field, this timely book fulfills the need to bring together the disparate parts of climate research on cities into a coherent framework. It is an ideal resource for students and researchers in fields such as climatology, urban hydrology, air quality, environmental engineering and urban design. © T. R. Oke, G. Mills, A. Christen, and J. A. Voogt 2017. All rights reserved.
... In this context, it is not surprising that the phenomenon of "urban heat islands" (UHIs), which characterises district heating, in comparison with the surrounding rural environment, has established itself as key a indicator of the urban climate [3,[17][18][19][20][21]. As an easy phenomenon to define and measure, this is the most studied of the effects of urban climate change. ...
... As an easy phenomenon to define and measure, this is the most studied of the effects of urban climate change. The mitigation of the effects of UHI through the spatial configuration of green spaces in the sustainable design of urban environments has thus become a matter of growing concern under climate change [3,[22][23][24][25][26][27][28][29][30][31][32][33][34][35]; these have been researched as supporting principles for the design and planning of Nature-Based Solutions (NBS) as mitigation strategies towards the negative effects of Climate Change in Urban Areas [36][37][38]. ...
... Land use changes in the urban surfaces (edification and surface imperviousness) as well as industry, traffic, and the general activities of the cities are the driving forces behind the increase in the sources of carbon dioxide emissions. These can be assumed to be the main drivers of global climate change [3,4]. ...
Understanding the thermal effects of different urban patterns that constitute today’s urban landscapes is critical to the development of urban resilience to climate change. This article aims to assess the efficiency of urban green spaces in thermal regulation. Through thermography, we explored the interaction between air temperature and the spatial components within these environments. Through comparative analysis involving a UAV, we studied the relationship between air temperatures at varying altitudes and the temperature within tree canopies. The results revealed significant differences in the thermal distribution between impervious urban areas with buildings and green spaces. These findings provide important information for assessing thermal comfort and the efficiency of urban green spaces in mitigating the impact of extreme heat events. During the summer months, green spaces, due to shade and the enhanced absorption of solar radiation by trees, exhibited lower temperatures compared to impervious areas. However, in winter, urban areas displayed higher temperatures, attributable to their heat retention capacity. This study contributes to the existing knowledge base by providing an in-depth examination of the thermal efficiency of urban green spaces across different layers of their lower atmosphere. Our results underscore the crucial role of tree cover in thermal comfort regulation, offering valuable information for sustainable urban planning. These insights are particularly relevant for the design of more comfortable and resilient environments in response to climatic variations and for the crafting of a tree-planting strategy in Mediterranean climate cities, an area where the impacts of climate change are becoming increasingly apparent.
... AH impacts the surface energy balance because it is related to the transfer of energy between land surface and atmosphere [2] and it is an important factor contributing to rising temperatures across the globe [3]. AH flux not only impacts the temperature, but it also results into release of air pollutants from domestic, industrial and vehicle emissions into the urban atmosphere [4]. These pollutants modify the net radiation budget and eventually warm up the ambient air. ...
... The urban fabric in cities is the roughest surface form [31]. The buildings are impermeable, hard and inflexible as compared to the vegetation due to which they reduce the wind flow causing surface drag [4]. Urban surface roughness is defined based on a set of parameters related to the urban morphology like zero plane displacement, roughness length, frontal area density, building plan area fraction, height to width ratio etc. and these can be estimated using morphometric or micrometeorological approaches. ...
... A comparison of the mean estimated albedo values and mean emissivity values from EO data based approach also shows close corroboration with the values found in literature. The calculated mean values of albedo and emissivity for all the LULC classes fall within the ranges defined by Oke et al. [4] in his study (Table 5). ...
Anthropogenic Heat (AH) emissions modify the energy balance in urban areas and is crucial for urban microclimate modelling and improved weather forecast modelling. Therefore, the present study conducted on Delhi and its surroundings firstly aims to estimate AH using Earth Observation (EO) data of Landsat 8 then, evaluate the impact of detailed urban roughness parameterization on the estimation of AH and further validate the obtained flux values with ground based observations of Large Aperture Scintillometer (LAS) setup. The study has been conducted over three time periods for October 2017, March 2018 and June 2018 by processing six Landsat tiles. Three methods have been employed on EO data for AH computation i.e. single urban roughness value for entire study area (Method 1), LULC based roughness values adopted from the literature (Method 2) and lastly, detailed pixel-by-pixel varying roughness values calculated from fine scale urban parameterization (Method 3) for each time period, The average AH values are higher for the month of June 2018: 359.91, 368.57 and 359.16 W/m2 as compared to month of March 2018 (322.44, 330.84 and 298.35 W/m2) and October 2017 (318.00, 331.04 and 306.71 W/m2) for method 1, method 2 and method 3 respectively. Net radiation and Sensible Heat Flux shows a good correspondence with in-situ measurements for most of the tiles and method 3 shows better spatial distribution of fluxes as compared to other two methods. However, due to difference in approach for estimation of fluxes (LAS setup computes latent heat flux as residual while EO based approach computes AH as residual), conclusive results could not be drawn with respect to aptness of a single method. Accurate estimation of AH in urban areas can assist further in formulating policies, regulations and action plans related to mitigation and control of heat stress, climate change and improved weather forecasting.
... As alterações nos processos de urbanização acarretam mudanças bruscas nos ambientes naturais e nos aspectos atmosféricos de uma cidade. Isso engloba modificações nas características termodinâmicas, hidrometeorológicas e físico-químicas, resultando em alterações nos balanços energéticos e hidrológicos naturais (OKE et al., 2017). Portanto, é importante compreender a necessidade e a amplitude dos estudos voltados para a análise do clima urbano, tanto na área da arquitetura quanto na geografia. ...
RESUMO O objetivo deste artigo é analisar o aspecto urbano e climatológico do bairro da Várzea, utilizando os três subsistemas propostos por Monteiro (1976) no Sistema Climático Urbano (SCU). A metodologia da pesquisa consistiu em quatro etapas: I) Análise termodinâmica; II) Análise hidrometeorológica; III) Análise físico-química; e IV) utilização de softwares específicos para cada uma dessas etapas. Para processar os dados, foram realizadas análises no Excel, interpolação de dados em softwares e revisão bibliográfica na área de estudo, o que permitiu uma complementação dos resultados. No subsistema termodinâmico, os dados indicaram a ocorrência de inversão térmica durante a noite. No subsistema hidrometeorológico, o processo de interpolação revelou áreas de vulnerabilidade durante o quadrimestre chuvoso no bairro. Já no subsistema físico-químico, de caráter exploratório, foi possível identificar de forma mais qualitativa a emissão de gases estufa em alguns locais da cidade de Recife, destacando a necessidade de estudos mais aprofundados nessa temática. Assim, os resultados obtidos permitiram uma avaliação do espaço como uma ferramenta conjunta de análise para o clima urbano, identificando pontos comuns de potencialidade ou vulnerabilidade. Essa abordagem integrada é fundamental para compreender e tomar medidas eficazes no planejamento urbano e no enfrentamento das mudanças climáticas. ABSTRACT The objective of this article is to analyze the urban and climatological aspect of the Várzea neighborhood, using the three subsystems proposed by Monteiro (1976) in the Urban Climatic System (UCS). The research methodology consisted of four steps: I) Thermodynamic analysis; II) Hydrometeorological analysis; III) Physical-chemical analysis; and IV) use of specific software for each of these steps. To process the data, analyzes were carried out in Excel, data interpolation in software and a bibliographic review in the study area, which allowed a complementation of the results. In the thermodynamic subsystem, the data indicated the occurrence of thermal inversion during the night. In the hydrometeorological subsystem, the interpolation process revealed areas of vulnerability during the rainy quarter in the neighborhood. In the physical-chemical subsystem, of an exploratory nature, it was possible to identify in a more qualitative way the emission of greenhouse gases in some places in the city of Recife, highlighting the need for more in-depth studies on this subject. Thus, the results obtained allowed an evaluation of the space as a joint analysis tool for the urban climate, identifying common points of potentiality or
... The atmosphere-biosphere-surface coupling was treated with the Community Land 180 Model (CLM) version 4.5 (Oleson et al., 2013) land-surface scheme and to account for the urban scale processes, the CLMU module within CLM4.5 was used (Oleson et al., 2008(Oleson et al., , 2010. CLMU adopts the classical canyon geometry approach, i.e. cities are represented as networks of street-canyons with specified geometry and surface parameters (Oke et al., 2017). RegCM was offline coupled to CAMx using the RegCM2CAMx interface developed by Huszar et al. (2012). ...
The rural-to-urban transformation (RUT) is the process of turning rural or natural land-surface into urban one which brings important modifications in the surface causing well know effects like the urban heat island (UHI), reduced wind-speeds, increased boundary layer heights and so on. Moreover, with concentrated human activities RUT introduces new emission source which greatly perturbs the local and regional air-pollution. Particulate matter (PM) is one of key pollutants responsible for deterioration of urban air-quality and is still a major issue in European cities with frequent exceedances of limit values. Here we introduce a regional chemistry-climate model (regional climate model RegCM coupled offline to chemistry transport model CAMx) study which quantifies how the process of RUT modified the PM concentrations over central Europe including the underlying controlling mechanisms that contribute to the final PM pollution. Apart from the two most studied ones, i) the urban emissions and ii) the urban canopy meteorological forcing (UCMF, i.e. the impact of modified meteorological conditions on air-quality) we analyze also two less studied contributors to the RUT’s impact on air-quality: iii) the impact of modified dry-deposition velocities due to urbanized land-use and iv) the impact of modified biogenic emissions due to urbanization induced vegetation modifications and changes in meteorological conditions which affect these emissions. To calculate the magnitude of each of these RUT contributors, we perform a cascade of simulations were each contributor is added one-by-one to the reference state while focus is given on PM2.5 (particulate matter with diameter less then 2.5 µm). We also look at their primary and secondary components, namely primary elemental carbon (PEC), sulphates (PSO4), nitrates (PNO3), ammonium (PNH4) and secondary organic aerosol (SOA). The validation using surface measurements showed a systematic negative bias for the total PM2.5 which is probably caused by underestimated organic aerosol and partly by the negative bias in sulphates and elemental carbon. For ammonium and nitrate, the underestimation is limited to the warm season while for winter, the model tends to overestimate their concentrations. However, in each case, the annual cycle is reasonably captured. We evaluated the RUT impact on PM2.5 over an ensemble of 19 central European cities and found that the total impact of urbanization is about 2–3 and 1–1.5 µgm−3 in winter and summer, respectively. This is mainly driven by the impact of emissions alone causing a slightly higher impact (1.5–3.5 and 1.2–2 µgm−3 in winter and summer), while the effect of UCMF was a decrease at about 0.2–0.5 µgm−3 (in both seasons) which was mainly controlled by enhanced vertical eddy-diffusion while increases were modelled over rural areas. The transformation of rural land-use into urban one caused an increase of dry-deposition velocities by around 30–50 % which alone resulted in a decrease of PM2.5 by 0.1–0.25 µgm−3 in both seasons. Finally, the impact of biogenic emission modification due to modified land-use and meteorological conditions caused a decrease of summer PM2.5 of about 0.1 µgm−3 while the winter effects were negligible. The total impact of urbanization on aerosol components is modelled to be (values indicate winter and summer averages) 0.4 and 0.3 µgm−3 for PEC, 0.05 and 0.02 µgm−3 for PSO4, 0.1 and 0.08 µgm−3 for PNO3, 0.04 and 0.03 µgm−3 for PNH4 and 0 and 0.05 µgm−3 for SOA. The main contributor of each of these components was the impact of emissions which was usually larger than the total impact due to the fact that UCMF counteracted with a decrease. For each aerosol component the impact of modified DV was a clear decrease of concentration and finally, the modifications of biogenic emissions impacted predominantly SOA causing a summer decrease while a very small secondary effect of secondary inorganic aerosol was modelled too (they increased). In summary, we showed that when analyzing the impact of urbanization on PM pollution, apart from the impact of emissions and the urban canopy meteorological forcing, one has to consider also the effect of modified land-use and its impact on dry-deposition. These were shown to be important in both seasons. For the effect of modified biogenic emissions, our calculations showed that it acts on PM2.5 predominantly trough SOA modifications which turned to be important only during summer.
... Through our assessment of some basic urban planning and landscape-architectural design decisions, we have identified the importance of spatial building blocks on mass-traffic flows, microclimatic conditions and air quality in urban space. More open areas allow for higher levels of air circulation, providing greater opportunities for pollutant removal, which is consistent with the findings of similar studies (Fu et al., 2017;Oke et al., 2017;Vardoulakis et al., 2002). Reduced air circulation capacity leads to a limited ability to disperse pollutants and to exchange air with the surroundings and the upper atmosphere. ...
Environmental modelling software can be useful for evaluating design interventions and formulating strategies to achieve a specific purpose, such as providing outdoor thermal comfort. It is less commonly used in predicting the dispersion of street pollutants. The aim of this research is to test selected morphological patterns with respect to their influence on wind conditions and the transport of traffic pollutants, and to verify the results against previous studies. The objective of the research is to evaluate relations between building typology in interactions with urban atmosphere. The method utilises a wind tunnel simulation with a static line source of emissions. Experiment results show that the exposed urban morphology models display an impact on flow conditions and consequently on the dispersion of traffic pollutants. At the same time, the results highlight the importance of urban aerodynamic perspective, particularly of urban spaces that can be expected to be subject to higher traffic pollutants in terms of urban air pollution.
... This block of altitude composes the atmospheric boundary layer (ABL), a spatially and temporally dynamic portion of the atmosphere that is also characterized by persistent turbulence [7]. With many AAM operations tailored for the urban environment, a large number of operations will take place within the urban boundary layer (UBL), a portion of the ABL that is influenced by the presence of a city [8]. Since the properties of the UBL tend to reflect those of the underlying surface, which hosts more roughness elements (e.g., buildings) and possesses more surface inference for extending these estimates to all other points within the area of interest using selective CFD simulations [25]. ...
This paper presents enhancements to, and the demonstration of, the General Urban area Microclimate Predictions tool (GUMP), which is designed to provide hyper-local weather predictions by combining machine-learning (ML) models and computational fluid dynamic (CFD) simulations. For the further development and demonstration of GUMP, the Embry–Riddle Aeronautical University (ERAU) campus was used as a test environment. Local weather sensors provided data to train ML models, and CFD models of urban- and suburban-like areas of ERAU’s campus were created and iterated through with a wide assortment of inlet wind speed and direction combinations. ML weather sensor predictions were combined with best-fit CFD models from a database of CFD flow fields, providing flight operational areas with a fully expressed wind flow field. This field defined a risk map for uncrewed aircraft operators based on flight plans and individual flight performance metrics. The potential applications of GUMP are significant due to the immediate availability of weather predictions and its ability to easily extend to arbitrary urban and suburban locations.
Urban Dry (Wet) Islands’ (UDI/UWI) represents microclimate change that impacts ecosystems and human well-being. However, causes of the UDI (UWI) phenomena are not fully understood due to the lack of empirical data. Here, we quantify UDI (UWI) using global observations of atmospheric humidity, evapotranspiration (ET), and land surface characteristics across 25 large urban agglomerations. We show that UDI (17) and UWI (8) are closely tied to local ET, global warming, and ‘Urban Heat Islands’ through intertwined linkages with water and energy balances. UDI is most pronounced in humid vegetated regions where mean urban-rural annual ET differences are as high as 215 mm, whereas UWI is found in arid regions or in climates with dry summers. We conclude that ET can be used as a single variable to explain emerging urban environmental changes. Our study supports a concerted strategy of restoring nature’s ET power as effective ‘Nature-based Solutions’ to mitigate the negative environmental effects of urbanization.
Die Auswirkungen des Klimawandels beeinträchtigen die Lebensqualität in den Städten und stellen eine Bedrohung für die Stadtbewohner:innen dar. Räumlich geplante und verwaltete Anpassungsmaßnahmen wie multifunktionale Blaugrüne Infrastrukturen sind in der Lage, steigenden Temperaturen und häufigeren und extremeren Hitzewellen und Niederschlagsereignissen entgegenzuwirken. Damit jedoch insbesondere die grüne Infrastruktur die Verdunstungskühlung zur Minderung der Temperaturen aufrechterhalten kann muss sie ausreichend mit Wasser versorgt werden. Dies gestaltet sich, in Anbetracht länger anhaltender Trockenperioden, immer schwieriger, weshalb auf lange Sicht neue innovative Lösungsansätze ausgearbeitet werden müssen. Auf Basis eines Modellierungsansatzes zur Analyse kleinräumiger Land-Atmosphären-Interaktionen und Messungen vor Ort, zeigen wir die Auswirkungen unterschiedlicher Oberflächengestaltungsmöglichkeiten auf die lokale Wasser- und Energiebilanz an der Oberfläche. Die Erfahrungen aus zwei konkreten Platzumgestaltungen in Innsbruck (Österreich) aus den Projekten cool-INN (abgeschlossen) und COOLYMP (laufend) zeigen, dass integrale Planung Blaugrüner Infrastruktur aus grauen Plätzen in Städten, selbst wenn sie mit einer Tiefgarage unterbaut sind, eine generationenübergreifende Wohlfühloase machen kann. Damit jedoch ein Übergang von klimafitten zur klimaresistenten Platzumgestaltung, und in weiterer Folge zur klimaresistenten Stadtplanung, gelingen kann, ist ein strategisches und nachhaltiges Wassermanagement erforderlich, das für eine ausreichende Wasserverfügbarkeit zur Unterstützung der ökologischen Systeme und Aufrechterhaltung des Kühleffekts, sorgt.
In the city of Erzurum, located in a cold climate region, it is important for pedestrian walkways and parks to be usable all year round. Haydar Aliyev Street, located on the city's new development axis, serves as both a pedestrian route and a park. Meteorological data was collected hourly throughout 2021 using a Vantage Pro 2 Plus device installed at a height of 1.5 m in the study area. The scenarios were analyzed using the ENVI-met BIO+ Science Software, with August (summer) and January (winter) identified as the hottest and coldest months, respectively. Sky View Factor (SVF) analysis was conducted using fisheye lens photos taken from different points in the area. Four different landscape design scenarios were created for the study area, consisting of plants, water surfaces, soil, and grass. It was found that the temperature decreased by an average of 0.2°C in the summer scenario when the number of plants was increased by 20%. Furthermore, it was determined that the deciduous tree scenario provided better thermal comfort compared to the treeless soil scenario for a pedestrian-friendly park during the winter months. The inactive water scenario for summer and winter was found to increase wind speed by a maximum of 1.3 m s-1. The study concluded that different landscape design scenarios had an impact on outdoor thermal comfort and that further research was needed in this area. Such studies highlight the need for multidisciplinary teamwork to create healthy, sustainable, and livable urban environments in designing thermal-comfortable spaces.
High temperatures and heatwaves are becoming more frequent, but heat vulnerability is rarely considered within local authority city design and statutory land-use planning processes. Here, we describe an approach to assess heat vulnerability in Birmingham, the second largest city in the UK. The approach uses open access data and GIS techniques that are available for built environment practitioners. Heat vulnerability is assessed by combining four datasets: surface temperatures, Local Climate Zones, green space, and Indices of Multiple Deprivation. The assessment shows that central and eastern areas of Birmingham that have the most compact urban form, least green space, and highest levels of deprivation are most vulnerable to heat. We evaluated the approach against previous climate research, examined the approach and datasets at the local scale, and described how heat vulnerability can be (and is being) incorporated into decision making. This project combines three key innovations: (1) the decision-centric process that focuses the method on the decision that needs to be made, minimizing inertia related to scientific or modeling uncertainty and reducing resource-intensity; (2) the co-creation process with Birmingham City Council, who have statutory powers for planning within the city, thereby ensuring that heat vulnerability is embedded within decisions on the suitability, design, and location of sites for future development; and (3) the open access and technically appropriate methodology which can be applied to any urban area in the UK, using the open access datasets described here, or globally, using locally applicable data sources.
Heat island cooling strategies (HICSs) are used to mitigate urban heat island phenomena and adapt to climate change as proposed by the U.S. Environmental Protection Agency (EPA), the Intergovernmental Panel on Climate Change (IPCC), and the World Health Organization (WHO). This study investigated urban heat island reduction and assessed the cooling effect of HICSs under various temporal and spatial conditions in urban areas. The study area was the Mugye-dong urban area in South Korea. To identify the effectiveness of heat island cooling strategies (HICSs), unmanned aerial vehicle (UAV)-based remote sensing and microclimate sensors were used to generate land cover, sky view factor (SVF) distribution, and land surface temperature (LST) maps of the study area. Differences in cooling effect according to spatial density (SD) were identified by dividing the SVF into five intervals of 0.2. Temporal changes were investigated throughout the day and under cloudiness-based meteorological conditions affected by solar radiation or less affected by solar radiation. Lower SD was associated with a greater cooling effect; meteorological conditions affected by solar radiation had a stronger cooling effect. The variation of the daytime cooling effect increased with decreasing SD. The difference in cooling effect between morning and afternoon was <1 °C under conditions less affected by solar radiation. Under conditions affected by solar radiation, the maximum temperatures were −6.716 °C in urban green spaces and −4.292 °C in shadow zones, whereas the maximum temperature was −6.814 °C in ground-based albedo modification zones; thus, differences were greater under conditions affected by solar radiation than under conditions less affected by solar radiation. As a result, it was found that HICS show a high cooling effect, high diurnal variation, and high morning-afternoon deviation under weather conditions with low SD and under conditions affected by solar radiation. This study quantitatively calculated the cooling effect of HICSs applied in urban areas under various spatiotemporal conditions and compared differences by technology. Accordingly, it is believed that it will serve as a basis for supporting the practical effects of the concepts presented by international organizations for climate change adaptation.
Background
The urban heat island (UHI) phenomenon, resulting from rapid urbanization and aggravated by persistent climate change, is intensifying heat stress and temperature anomalies inside the urban microclimate, requiring the implementation of suitable adaptation measures for sustainable development. The integration of street trees inside the urban landscape is a strategy to alleviate the thermal stress of pedestrians. However, trees have variable potential for the regulation of thermal comfort depending on their different canopy shapes/drag. Therefore, a holistic understanding of tree plantings and species with respect to a particular climate is necessary for urban sustainability.
Methods
In this study, computational fluid dynamics (CFD) that employ unsteady Reynolds-averaged Navier-Stokes (URANS) equations were performed using FLUENT solver to analyze the cooling potential of isolated tree species based on 5 morphological characteristics and canopy shapes (i.e., tree height, trunk height, crown width, crown height, and leaf area density) in an urban area.
Results
Results revealed a variable temperature regulation (i.e., 0.6 to 1.2 °K) depending on the tree species. Overall, the cooling effect was only observed in the vicinity of the tree canopy. This was due to the availability of shading and increased moisture content provided by the canopy foliage, which blocked shortwave radiation from the sun, as compared to its surroundings.
Conclusions
The study findings show that leaf area density is the morphological trait that has the greatest impact on thermal comfort, as it results in low ambient air temperature irrespective of the type of urban density. Additionally, the most effective way to reduce thermal stress is to implement taller trees with uniform foliage density, which will produce a well-ventilated environment.
The impact of urban morphology on air quality, particularly within deep canyons with longer residence times for complex chemical processes, remains insufficiently addressed. A flexible multi-box framework was used to simulate air quality at different canyon heights (3 m and 12 m). This approach incorporated essential parameters, including ventilation rates, background concentrations, photochemical schemes, and reaction coefficients. A field campaign within a deep canyon with an aspect ratio of 3.7, in Naples, Italy was conducted and used for the model evaluation. The model performance demonstrated good agreement, especially at the street level, when employing a realistic light intensity profile and incorporating volatile organic compound (VOC) chemistry. Our findings indicate that peroxyl radical production affects NO2 and O3 levels by up to 9.5% in deep canyons and underscore the significance of vertical distribution (approximately 5% variance) in health assessments and urban air quality strategy development. The model response was sensitive to changes in emissions as expected, but also, somewhat more surprisingly, to background conditions, emphasizing that policies to remove pollution hotspots must include local and broader citywide action. This work advances the understanding of air quality dynamics in deep urban canyons and presents a valuable tool for effective air quality management in intricate urban environments.
Urban vegetation has a large impact on urban microclimates and is an important element in urban environmental design. Its representation within state of the art urban climate models provides new capabilities for urban planners and designers to consider the impact of trees on urban climates. However, assessing the climate impact of urban vegetation and evaluation of these models at the street scale demands spatial sampling of the important driving (solar and longwave radiation) and response (surface and air temperatures) variables at high spatial resolution. This project describes a mobile traverse methodology (MTM) capable of measuring, for the first time, representative values of radiative fluxes and surface temperatures within residential street canyons with complex vegetation assemblages. Traverses were conducted at select times over a day in three neighbourhoods with varying street tree canopy cover in London, ON, Canada. The system can differentiate unique spatial patterns of measured radiative fluxes and road surface temperatures between neighbourhoods with varying tree canopy cover. The associated distributions of \(T_{Road}\) and incident radiative fluxes provide a unique dataset to test numerical models that resolve within street-canyon vegetation.KeywordsUrban microclimateSurface temperatureClimate changeVegetation
In climate change adaptation and mitigation, including the reduction of negative impacts associated with urban heat environment, it is essential to quantify the contributions of natural and anthropogenic factors. Using remotely sensed land surface temperature, emissivity, land use types, and nightlight data for 364 Chinese cities, we proposed an urban land surface heat environment change attribution algorithm based on land use types, attributing the change of urban land surface heat environment to natural factors, land use change, and other anthropogenic factors at urban scale. From 2005 to 2020, summer daytime land surface temperature decreased and increased in 40.93% and 59.07% of these cities, respectively. Natural factors made a larger contribution than land use change and other anthropogenic factors to urban land surface temperature changes in 79.67% of cities; in 60.44% of cities, other anthropogenic factors other than land use change and natural factors experienced the highest contribution intensities. Three factors were spatially heterogeneous. Urban land surface temperatures were influenced by background natural climate endowment and human social development values, increasing with population density (up to 2,000 people·km−2) and annual precipitation (up to 800 mm·year−1). These results have important implications for the detection and attribution of urban-scale climate change and will be useful in designing management plans to optimize land use configuration, lead in climate actions, and carry out collaborative mitigation and adaptation strategies to achieve sustainable development.
The impacts of climate change, such as extreme events and progressive global warming, threaten the conservation and habitability of urban cultural heritage. Understanding climate risks to heritage must be part of planning and policy decision-making processes to increase the resilience and sustainability of both social and built environmental systems.. However, despite a large body of literature on climate-related hazards, there is a notable knowledge gap regarding a holistic conceptualization of hazards in historic urban areas, especially in the case of heat waves and urban heat island phenomena.The main goal of this study was to analyze and represent the interaction between historic built environment and heat waves via Geographic Information Systems (GIS) data, considering the vulnerability of historic areas both as urban systems and as heritage areas. To frame a holistic approach, socio-economic, cultural, governance (services and resources) and physical (gathering tangible characteristics of all infrastructures, elements and buildings) aspects of the system are taken into ac-count. To this end, a multicriteria risk assessment methodology is developed. Key performance indicators, criteria and requirements addressing relevant vulnerable elements of historic urban areas are identified for the development of the methodology. Moreover, as the foundation for the risk assessment, a categorization based on vulnerability to heat waves is proposed for both buildings and urban spaces. Here, this methodology’s results and its application on a GIS-based model in the historic area of Bilbao (Basque Country, Spain) are presented. This work aims to be replicable and to serve as a reference for future holistic assessments of heatwaves risks in historic urban areas worldwide.KeywordsHeritageClimate changeRisk assessmentVulnerabilityCategorizationKey Performance Indicators
Within the existing literature, there already is a wealthy initiation into how different types of local adaptation measures can help urban fabrics respond to increasing temperatures as a result of climate change. Arguably propelled by the climate change adaptation agenda, different typologies of thermal sensitive measures are becoming continually more organised and solidified to improve the bioclimatic responsiveness of the consolidated urban fabric. Along with this growing body of knowledge, is the recognition that the in-situ efficacy of different measure typologies in counteracting increasing urban heat levels depends on two interrelated factors, these being: (1) how well the dynamic microclimatic conditions are assessed and understood; and (2) how well characteristics such as urban morphology are understood. Following this line of reasoning, in order to be utilised to their full potential, and moreover avoid symptoms of mal-adaptation, thermal sensitive adaptation measures must account for the unremitting and symbiotic cause-and-effect between these factors. Today, it is widely known that mean radiant temperature (MRT) is one of the most significant factors upon human thermophysiological thresholds. In addition, it is furthermore a particularly dynamic variable as a result of the continuously shifting annual solstice. Accordingly, MRT must be understood as a variable which modifies not just on a diurnal bases, but in addition one which oscillates throughout the different months and seasons of the year. Depending on the time of year, as dictated by the Urban Energy Balance, radiation fluxes interact with the static structures of the urban fabric through different seasonal energy exchange patterns/quantities. Such an understanding calls upon the approach of both yearly and different seasonal analytical scopes to better comprehend the symbiotic relationship of urban morphology and solstice patterns. It permits a finer understanding of the impacts associated to crucial climatic variables that play a significant role in human thermal comfort. Invariably, this consequently includes the fundamental role of in-situ dynamic radiation fluxes that are undeniably dictated by modifying yearly/seasonal solstice patterns. Grippingly, and unlike encircling air temperature, MRT can more easily be manipulated through different measure typologies within the urban fabric, and in addition, presents means to alter the cause-and-effect relationship with other encircling microclimatic variables. Within this book chapter, a structured reflection will be undertaken for Ankara, Türkiye—and how an innovative methodical case study presents bioclimatic lessons pertinent to the crucial role of in-situ dynamic radiation fluxes within a densifying and warming urban fabric in an era of growing climate change.KeywordsPhysiologically equivalent temperatureUrban morphologyHeat/cold stress detectionIn-situ climatic adaptationClimate changeAnkara
Forecasts of a drastic increase in temperatures in the coming decades are driving the adoption of design strategies and solutions to improve the livability of urban environments. Increasing attention is being paid to the thermal comfort of open spaces by both designers and researchers. Nature-based solutions and man-made devices to improve the comfort of outdoor spaces during summer are spreading, but effective, easy simulation and design support tools for this purpose are still lacking, as most of the available software such as ENVI-met or RayMan cannot model such devices. As Physiological Equivalent Temperature (PET) is one of the most relevant and comprehensive indicators of Outdoor Thermal Comfort (OTC), this study aims to investigate PET variations of different artificial shading systems and propose a simplified methodology for assessing them through analytical simulations with RayMan software. When modeling the shading elements, the trick adopted for this purpose is to associate different cloud densities with the shading provided by the screens, thus overcoming a gap that affects the software. The procedure is digitally tested in a covered courtyard case study in Bologna (Italy). Diverse options proposed by the designers for textile screening materials have been compared, showing that these reduce by at least 1 °C the PET-gauged thermal stress. Beyond specific results, the main outcome of this study is the procedure developed to simulate sun-shading sail effects on OTC by means of RayMan, which can support designers in planning effective solutions for open space livability in summertime.
The current study investigated the impact of vegetation canopy on the outdoor thermal environment in cold winter and spring, a less-explored aspect of its climate effects. Firstly, we conducted on-site observations of meteorology parameters on a campus in a hot summer and cold winter region. Then the ENVI-met microclimate simulation model was utilized to simulate the air temperature, relative humidity, wind speed and direction, and solar radiation of typical winter and spring days. Furthermore, the PET index was calculated to evaluate the thermal conditions. Our findings revealed that during the daytime, the vegetation canopy raised air temperature and relative humidity, reduced wind speed, and mitigated solar radiation. Solar radiation emerged as the primary factor affecting thermal comfort in the cold winter and spring. The presence of deciduous broad-leaved vegetation notably reduced cold discomfort and improved thermal comfort in the cold winter and spring. Finally, we propose replacing evergreen broad-leaved vegetation with deciduous broad-leaved vegetation in hot summer and cold winter regions to ensure year-round thermal comfort, especially in the cold winter and spring.
The bryophyte flora of Vienna is documented only in parts. Old finds often appeared in publications about Lower Austria; only one study addressed the bryophytes of the inner city. Here, we present a bryophyte flora of Vienna, including historical reports and the results of recent investigations. From 1998 to 2023, we recorded 329 bryophyte taxa in Viennese urban territory. Fifty-six of these were liverworts, and 273 were mosses. Sixty-seven taxa are new for Vienna. Forty-nine taxa, given in historical studies, could no longer be found. If we also count these, 378 taxa occurred in Vienna to date. Of the current occurring bryophytes, 67 species have an endangerment classification. Rich in bryophytes were the dry grasslands of the Lobau, the oxbow lakes of the Lobau and the Prater, and large parts of the Wienerwald. But flat roofs and inner-city areas also showed more than 100 species. Compared to other European cities, Vienna is decidedly species-rich and highly responsible for some species in Austria. Reasons for this are the extensive green spaces and the pronounced climatic gradient from the sub-oceanic west to the sub-continental east of Vienna. Awareness raising for bryophytes we recommend in addition to the existing biotope protection.
In summertime and during heat events the urban heat island can negatively impact human health in urban areas. In the context of climate change, climate adaptation receives more attention in urban planning. Microscale urban climate modelling can identify risk areas and evaluate adaptation strategies. Concurrently, evaluating the model results with observational data is essential. So far, model evaluation is mostly limited to short-term field campaigns or a small number of stations. This study uses novel crowdsourcing data from Netatmo citizen weather stations (CWS) to evaluate the urban microscale model PALM for a hot day (Tmax ≥ 30°C) in Bochum in western Germany with anticyclonic atmospheric conditions. Urban-rural air temperature differences are represented by the model. A quality control procedure is applied to the crowdsourced data prior to evaluation. The comparison between the model and the crowdsourced air temperature data reveals a good model performance with a high coefficient of determination (R2) of 0.86 to 0.88 and a root mean squared error (RMSE) around 2 K. Model accuracy shows a temporal pattern and night-time air temperatures during the night are underestimated by the model, likely due to unresolved cloud cover. The crowdsourced air temperature data proved valuable for model evaluation due to the high number of stations within urban areas. Nevertheless, weaknesses related to data quality such as radiation errors must be considered during model evaluation and only the information derived from multiple stations is suitable for model evaluation. The procedure presented here can easily be transferred to planning processes as the model and the crowdsourced air temperature data are freely available. This can contribute to making informed decisions for climate adaptation in urban areas.
Urban green spaces provide ecosystem services that directly or indirectly benefit people, however, urban growth (especially in developing countries) generates the loss of these green areas and consequently of their ecosystem services. This paper aims to present the effects of land use and land cover changes in the last 30 years on two basic urban ecosystem services, water flow regulation and local and regional climate in two of main Latin American megacities (São Paulo and Mexico City). The study focuses on urban green spaces because they reduce the urban heat island effects, improve air quality, create habitats for biodiversity conservation, provide cultural services, and contribute to flooding prevention and groundwater conservation. A spatial analysis with the aid of geographic information systems was performed to assess (i) the urbanization process of the Metropolitan Areas of both cities over time; (ii) how this process generated changes in the land cover in both metropolises, and (iii) how these changes caused environmental negative impacts on ecosystem services. The loss of green areas as a consequence of urban expansion in the Metropolitan Areas of São Paulo and Mexico City changed the spatial distribution of urban heat island and increased the surface runoff, generating floods during the rainy periods. Our results suggest the urgent need for implementation of ecosystem-based spatial planning and ecological restoration of urban green areas in both studied cities to prevent further losses in ecosystem services and to improve the quality of life of urban inhabitants.
Few publications have considered the urban heat island (UHI) effect in small settlements. This paper, therefore, presents the findings of a UHI study conducted in the small, mid-latitude city of Inverness, Scotland (population: 63,220). The study aimed to provide an initial appraisal of the scale of UHI phenomena in Inverness and to understand the factors associated with its presence. Mobile vehicular traverses of a study transect were conducted on 30 dates during June, July & August 2019. Measurements of near-surface air temperature were recorded at 19 local climate zone observation points between 20:00 and 23:00 BST. Daily mean UHI intensity (UHII) during the study ranged from 0.7 to 3.5°C, with an overall mean UHII of 1.6°C. Land use characteristics impacted the UHII, with areas with higher fractions of impervious surface cover returning significantly higher air temperatures. UHII increased with the onset of sunset, and the highest UHII occurred on dates with up to 1–2 oktas of cloud cover, low relative humidity, and high cloud base height. The results align with previous studies and comparisons are drawn between Inverness and other settlements globally. Further research in Inverness is recommended to better understand UHI effects and influence national planning policy.
A comprehensive comparison of the trends and drivers of global surface and canopy urban heat islands (termed Is and Ic trends, respectively) is critical for better designing urban heat mitigation strategies. However, such a global comparison remains largely absent. Using spatially continuous land surface temperatures and surface air temperatures (2003–2020), here we find that the magnitude of the global mean Is trend (0.19 ± 0.006°C/decade, mean ± SE) for 5,643 cities worldwide is nearly six‐times the corresponding Ic trend (0.03 ± 0.002°C/decade) during the day, while the former (0.06 ± 0.004°C/decade) is double the latter (0.03 ± 0.002°C/decade) at night. Variable importance scores indicate that global daytime Is trend is slightly more controlled by surface property, while background climate plays a more dominant role in regulating global daytime Ic trend. At night, both global Is and Ic trends are mainly controlled by background climate.
Blue–green infrastructures (BGI) play an important role in addressing contemporary challenges posed by urbanization, climate change, and demographic shifts. This study focuses on the parameterization of BGI within hydrological models, specifically emphasizing the Low Impact Development (LID) module of the Storm Water Management Model (SWMM), supplemented by the SWMM-UrbanEVA evapotranspiration model. Employing a systematic approach, a transferable framework is developed to categorize BGI types, leading to a comprehensive parameterization toolset. This toolset includes parameter estimates for predefined BGI types, encompassing both natural and technical systems with a specific emphasis on plant-specific parameterization. The justification of these parameter estimates is supported by an extensive literature review. Sensitivity analyses reveal the influence of plant-specific parameters, such as the crop factor (KC), and soil storage capacity, on water balance and peak runoff. Additionally, this study presents practical guidelines to enhance the comprehension of model behavior and ensure the highest possible quality in model parameterization. While further research on validity and transferability of the toolset is required, the findings of this study provide useful support for the differentiated representation and analysis of hydrological processes in urban environments. As a result, this study serves as a valuable resource for researchers, practitioners, and decision makers, facilitating the implementation of sustainable water management practices in urban settings.
Achieving climate neutrality by 2050 requires ground-breaking technological and methodological advancements in climate change mitigation planning and actions from local to regional scales. Monitoring the cities' CO2 emissions with sufficient detail and accuracy is crucial for guiding sustainable urban transformation. Current methodologies for CO2 emission inventories rely on bottom-up (BU) approaches which do not usually offer information on the spatial or temporal variability of the emissions and present substantial uncertainties. This study develops a novel approach which assimilates direct CO2 flux observations from urban eddy covariance (EC) towers with very high spatiotemporal resolution information from an advanced urban BU surface flux model (Part 1 of this study, Stagakis et al., 2023) within a Bayesian inversion framework. The methodology is applied to the city centre of Basel, Switzerland (3 × 3 km domain), taking advantage of two long-term urban EC sites located 1.6 km apart. The data assimilation provides optimised gridded CO2 flux information individually for each urban surface flux component (i.e. building heating emissions, commercial/industrial emissions, traffic emissions, human respiration emissions, biogenic net exchange) at 20 m resolution and weekly time-step. The results demonstrate that urban EC observations can be consistently used to improve high-resolution BU surface CO2 flux model estimations, providing realistic seasonal variabilities of each flux component. Traffic emissions are determined with the greatest confidence among the five flux components during the inversions. The optimised annual anthropogenic emissions are 14.7 % lower than the prior estimate, the human respiration emissions have decreased by 12.1 %, while the biogenic components transformed from a weak sink to a weak source. The root-mean-square errors (RMSEs) of the weekly comparisons between EC observations and model outputs are consistently reduced. However, a slight underestimation of the total flux, especially in locations with complex CO2 source/sink mixture, is still evident in the optimised fluxes.
Rapid urbanization and global climate change are likely to exacerbate urban flooding intensity, frequency and uncertainty. Thus, it is fundamental and crucial to investigate the dominant influencing factors for the mitigation of urban flooding. However, knowledge about the influence of building patterns on urban flooding remains limited. Taking Beijing, a typical megacity, as a case study area, we quantified the importance of building patterns and their interaction effect at the subwatershed scale using the boosted regression tree and geographical detector model. The results indicated that (1) the landscape shape index, slope, green space ratio and waterbody ratio were the most important influencing factors determining urban flooding, with a total relative contribution of 67.23%; (2) building metrics had a certain impact on urban flooding, and the sum of the relative contribution reached 21.03%; (3) the landscape shape index, slope, and green space ratio exhibited a combination of negative and positive correlations with urban flooding density; and (4) an enhancement effect existed between building metrics, especially the building congestion degree and building density. These findings provide quantitative insights on rational urban morphology planning which could be applied to improve stormwater management and promote urban sustainability in megacities.
Injecting volcanic gas into the air leads to an increase in carbon dioxide (CO2) levels compared with background concentrations and may establish gas hazard conditions. This study reports the results of five stable isotope (i.e., δ¹³C‐CO2 and δ¹⁸O‐CO2) surveys of airborne CO2 on Vulcano from August 2020 to November 2021. To measure CO2 in the air, a mobile laboratory was equipped with a laser‐based spectrophotometer that can selectively detect different CO2 isotopologues. Volcanic CO2 has a different isotopic signature than atmospheric CO2 and both δ¹³C‐CO2 and δ¹⁸O‐CO2 can help trace the injections of volcanic gases into the air. An isotopic mass balance model was developed for partitions CO2 between atmospheric background and volcanic CO2. The results of these studies show that volcanic CO2 emissions and atmospheric circulation deeply affected the concentration of CO2 in the air at Vulcano Porto. Studies of δ¹³C‐CO2 and δ¹⁸O‐CO2 provide an estimate of volcanic CO2 in the air. These results help identify spatially some points of interest for mitigating volcanic gas emission‐related hazards on Vulcano.
In this study; the outdoor thermal comfort of the users of two urban plazas with different morphologies in Annaba city, Algeria, have been evaluated. First, field measurements of the microclimatic parameters took place; namely the air temperature and the relative humidity in the two urban plazas, during hot days. Then, these measurements were compared with the results of the numerical simulations carried out by ENVI-met software in order to validate the model. The outdoor thermal comfort was evaluated by microclimatic measurements as well as a questionnaire survey consisting of interviews during the measurement days. The main objective was to determine the neutral Physiological Equivalent Temperature (PET) and to examine the influence of urban microclimatic conditions on the subjective thermal perception of people, as well as to compare it with different indexes of thermal comfort. Hence, the aim was to compare the microclimatic parameters of the two plazas, with and without vegetation and to see their impact on the thermal comfort indices. The results show that there is a difference between the two morphologies. Moreover, vegetation and urban morphology influence the neutral values of the thermal comfort indices.
Construction of urban green and blue spaces (UGBS) has long been proved as an effective mitigation to urban heat island effect. Yet we spotted a rarity of studies evaluating UGBS’s climatic effect difference in different land-uses, and a rarity of empirical evidence on better UGBS allocation for better cooling. In this study, we conducted field measurements of nighttime air temperature (Ta) and relative humidity (Rh) along an enclosed transect at the core area of Beijing, China, and evaluated the contributions of UGBS on local-scale climate. Land-cover types and land-use classification scheme Local Climate Zone (LCZ) were used to analyze measured Ta and Rh. Urban vegetation coverage is further intersected with LCZs to evaluate vegetation’s cooling and humidifying effects in different land-uses. Results show that better correlations were generally detected with larger buffer zones when more land-cover and land-use conditions were included. UGBS exhibit significant cooling and humidifying effects, and better regression models were built when green and blue spaces were taken as a whole rather than independently. Coverage of LCZ 1 (compact high-rise), LCZ 2 (compact midrise) and LCZ G (water coverage) were found to more significantly contribute to local-scale climate. Increasing vegetation coverage in LCZ 2 and LCZ 3 is expected to facilitate better cooling and humidifying effect. Results of this study may provide insights for practitioners to allocate UGBS for better urban cooling.
Citation: Yılmaz, S., Bilge, C. & Irmak, M. A. (2023). Determining the climate future projection of Erzurum City with the UrbClim model. Abstract The negativities brought by climate change, which is among the crisis agendas today, directly affect the cities. According to the UN, the rate of urbanization in the world is increasing rapidly. It is estimated that it will reach 6.4 billion in 2050. The UrbClim model is also used to project future climate in cities. For the province of Erzurum, where the climate negatively affects living things, the climate data of the city for the first 10 days of July 2016, 2017, and 2018 were analyzed using the UrbClim model. This study, it is aimed to analyze the exemplary cities with cold climates in the world, which will set an example in the determination of climate change and support sustainable and livable urbanization, use energy efficiently, and to produce climate adaptation strategies at the point related to landscape.
Urban morphology quantitatively expresses a city’s spatial structure, internal relationships, and physical form. It has advantages for predicting urban growth and analyzing the current state of cities in the literature. A comprehensive study on the complex relationships between urban morphology and urban heat island intensity (UHII) is of great importance for mitigating the urban heat island (UHI) effect for megacities. This study models urban morphological indicators in fine resolution based on three aspects: building morphology, ecological infrastructure, and human activities. The model accurately captures UHII by employing the definition of UHI effects. The relationship between urban morphology and UHII was further examined using extreme gradient boosting (XGBoost) and Shapley additive explanations (SHAP). By taking central Beijing, China as study area, major findings include the following: (1) Significant daytime UHI effects were observed within the research area, particularly during the summer months, when it appears to be most severe. More than 90% of the region experiences varying degrees of the UHI effects. (2) UHI is significantly correlated with both 2D and 3D urban morphological indicators. Low sky view factor (SVF) and high SVF tend to mitigate UHI, whereas moderate SVF tends to aggravate UHI. (3) In densely populated areas, tall trees may be more effective than other forms of vegetation at mitigating UHI. Based on the aforementioned findings, this article suggests that urban morphology optimization should focus on seasonality, spatial specificity, and indicator specificity for megacities in urban design and spatial planning aimed at mitigating UHI.
Urban heterogeneity, such as the variation of street layouts, building shapes, and building heights, cannot be fully represented by density parameters commonly used in idealized urban environmental analyses. To address this shortcoming and better model flow fields over complex urban neighborhoods, we propose two novel descriptive geometric parameters, alignedness and building facet entropy, which quantify the connectivity of inter‐building spaces along the prevailing wind direction and the variation of building facet orientations, respectively. We then conducted large eddy simulations over 101 urban layouts, including realistic urban configurations with uniform building height as well as idealized building arrays with variable heights, and evaluated the resulting bulk flow properties. Urban canopy flow over realistic neighborhoods resembles staggered building arrays for low urban densities but becomes similar to aligned configurations beyond λp ∼ 0.25 where the realistic flow is less sensitive to changes in density. We further show that compared to traditional density parameters (such as plan and frontal area densities), the mean alignedness, a measure of connectivity of flow paths in street canyons, better predicts canopy‐averaged flow properties. Furthermore, for realistic urban flow, the dispersive momentum flux shows a clear increasing trend with building density, and a decreasing trend with alignedness, which is in contrast with idealized cases that exhibit no clear trend. This distinct behavior further highlights the necessity of evaluating flow over realistic urban layouts for flow parameterization. This study provides an improved method of describing urban layouts for flow characterization that can be applied in neighborhood‐scale urban canopy parameterization.
In this study, we investigated the association between weather type (WT) and urban heat island intensity (UHII) in the region of Attica (Greece). The application of the methodology resulted in ten WTs over the Attica region. The UHII was calculated for every hour of the day from 2008 to 2017, using a new air temperature dataset produced by Copernicus Climate Change Service. To obtain more definitive findings about the relationship between WTs and UHII, we also used the upper 5% of UHII (urban overheating, UO). UO was estimated for two time intervals (daytime and nighttime) and for the warm period (June–September). The UHII frequency distribution, as well as the spatiotemporal characteristics of the UO, were also investigated. It was found that UO was amplified under WT2 during the night, while WT10 was mainly related to increased UO magnitudes in the daytime in all months. Furthermore, analysis results revealed that the UO effect is more pronounced in Athens during the night, especially at the Athens center. The daytime hot spots identified were mainly in suburban and rural areas. Therefore, this methodology may help with heat mitigation strategies and climate adaptation measures in urban environments.
Artificial intelligence technologies such as computer vision (CV), machine learning, Internet of Things (IoT), and robotics have advanced rapidly in recent years. The new technologies provide non-contact measurements in three areas: indoor environmental monitoring, outdoor envi-ron-mental monitoring, and equipment monitoring. This paper summarises the specific applica-tions of non-contact measurement based on infrared images and visible images in the areas of personnel skin temperature, position posture, urban physical environment, building construction safety, and equipment operation status. At the same time, the challenges and opportunities as-sociated with the application of CV technology are anticipated.
O presente artigo faz uma discussão metodológica sobre o tamanho da área, da qual deriva a temperatura do ar, lida por um sensor. Essa discussão se dá através da revisão da produção da Geografia Climatológica Brasileira e de uma investigação empírica considerando o sítio, o padrão de urbanização brasileiro, os equipamentos normalmente utilizados e nosso clima tropical. Elementos que divergem muito dos quais se deparam pesquisadores estrangeiros de referência. Baseando-se no levantamento bibliográfico, são definidos raios de 25, 50, 100, 150 e 200 metros correlacionados com a temperatura do ar e com o grau de impermeabilidade do solo em 8 pontos distintos da cidade de Ubá-MG. Chegou-se à conclusão que áreas de origem muito grandes (com raios maiores que 150m) ou áreas com raios muito pequenos (como 25m) não conseguem explicar bem a temperatura do ar em relação a área urbanizada desses pontos. Foi encontrado um melhor ajuste com raios de 50m e 100m em torno dos pontos, sendo 100m mais adequados para áreas menos adensadas e 50m para áreas mais densas com cânions urbanos mais profundos.
This study analyses budgets of second-order turbulence moments over a real urban canopy using large-eddy simulation. The urban canopy is representative of the City of Boston, MA, United States and is characterized by a significant height variability relative to the mean build- ing height. The budgets of double-averaged Reynolds-stress components, scalar fluxes, and scalar variances are examined with a focus on the importance of the dispersive terms above the mean building height. Results reveal the importance of the wake (dispersive) production term, in addition to the shear production term, in the turbulence kinetic energy (TKE), stream- wise velocity variance and scalar variance budgets well above the mean building height. In this region, the turbulent and dispersive transport terms are smaller than the production and dissipation terms. Nonetheless, the dispersive transport terms in the TKE and scalar variance budgets can be as important as their turbulent counterparts. The subgrid-scale dissipation term is the main sink in the TKE, vertical velocity variance and scalar variance budgets. In the momentum and scalar flux budgets, the pressure-strain correlation term and the pressure gradient-scalar interaction term are the significant sink terms, respectively. Our analysis high- lights the complexity associated with the budgets of second-order turbulence moments over real urban canopies and has important implications for developing urban parameterizations for weather and climate models.
High-resolution numerical weather prediction experiments using the Global Environmental Multiscale (GEM) model at a 250-m horizontal resolution are used to investigate the effect of the urban land-use on 2-m surface air temperature, thermal comfort, and rainfall over the Montreal (Canada) area. We focus on two different events of high temperatures lasting 2–3 days followed by intense rainfall: one is a large-scale synoptic system that crosses Montreal at night and the other is an afternoon squall line. Our model shows an overall good performance in adequately capturing the surface air temperature, dew-point temperature and rainfall during the events, although the precipitation pattern seems to be slightly blocked upwind of the city. Sensitivity experiments with different land use scenarios were conducted. Replacing all urban surfaces by low vegetation showed an increase of human comfort, lowering the heat index during the night between 2° and 6°C. Increasing the albedo of urban surfaces led to an improvement of comfort of up to 1°C during daytime, whereas adding street-level low vegetation had an improvement of comfort throughout the day of up to 0.5°C in the downtown area. With respect to precipitation, significant differences are only seen for the squall line event, for which removing the city modifies the precipitation pattern. For the large-scale synoptic system, the presence of the city does not seem to impact precipitation. These findings offer insight on the effects of urban morphology on the near-surface atmospheric conditions.
detection of their spatiotemporal changes, which have been well addressed in spatial statistics. The current study aimed to
detect the spatiotemporal changes of surface urban heat islands (SUHI) in Tehran metropolis during the daytime/nighttime
at monthly and seasonal scales and over the warm and cold periods of the year. The consequences of many elements like
as daytime/nighttime land surface temperature (LST) extracted by the MODIS/006/MOD11A1 and the NDVI extracted by
MODIS/006/MOD13A2 over a 20-year period (2001–2020) were first investigated. Then, the SUHI index was computed
for the study area. The correlations between the heat islands and urban land use (traffic, population density, airport, etc.),
air pollutants (CO, NO2, SO2, etc.), and NDVI were investigated in the next stage. Finally, Moran’s algorithm was used to
measure the spatial autocorrelation, and Gi statistic was used to analyze the cold and warm spots. The results indicated that
the LST trend was constant during the daytime/nighttime, and the NDVI also had a slight rising trend. The results of the
SUHI maps indicated that the zones with heat islands during the daytime over the seasons’ warm and cold times are located in
the south, southeast, and west of the city. During the nighttime, the central zones of the city as well as some parts in the east
and southeast have had higher heat islands. The results of the correlation between the heat islands and land use, vegetation,
and air pollutants indicated a direct correlation between the heat islands and the airport and industrial land use over time,
while it was inversely correlated with other land uses. During the nighttime, all land uses had a direct correlation with the
heat islands. Regarding the air pollutants, PM2.5 and PM10 were most correlated with the heat islands during both daytime/
nighttime while other pollutants have been inversely correlated. The heat islands and the NDVI were also inversely correlated
during both daytime/nighttime. The OLS (ordinary least-squares) model results also indicated that the R2 values during the
daytime/nighttime were 0.70 and 0.59, respectively, over the cold period of the year, compared to values of 0.69 and 0.68
over the warm period of the year. The results of global Moran’s I and G*i statistics also indicated that the heat islands of the
Tehran metropolis had a spatial structure distributed in a cluster in which the southern, western, southwestern, and northern
parts had warm spots during the daytime and cold spots during the nighttime. Moreover, the northern and northeastern parts
had cold spots during the daytime, and the central and eastern parts had warm spots during the nighttime.
Substantial reductions in human and economic activities such as road traffic for several months in 2020 were one of the consequences of the Coronavirus pandemic. This unprecedented change in urban metabolism also affected temperature and air pollutants. This study investigates the effects of the first COVID-19 lockdown across 43 cities in Europe. It determines the influence of anthropogenic activities on nitrogen dioxide (NO2), ozone (O3), and particulate matter (PM2.5), as well as on land surface temperature (LST) and the surface urban heat island intensity (SUHII) using satellite, modeled, and mobility data. Our findings show that there are great temporal and spatial differences and distinct patterns between the cities regarding the magnitude of change in the variables under study. In general, the results indicate a substantial decrease in NO2 concentrations in most of the studied cities compared with the reference period of 2015–2019. However, reductions could not be attributed to mobility changes such as less traffic at transit stations, contrary to the results of previous studies. O3 levels increased during the first lockdown in accordance with the decreasing NO2 concentrations. The PM pattern was inconsistent over time and space. Similar to the NO2 results, no relation to the altered mobility behavior was found. No clear signal could be detected for LST and the SUHII, likely due to dominating meteorological influences.
Based on the daily observational data of air temperature and the soil temperature at a depth of 0–320 cm at the Shijiazhuang urban meteorological station and two nearby rural stations from 2009 to 2012, urban heat island (UHI) effect from the canopy to the surface and deep layers of soil at Shijiazhuang urban station were compared and analyzed. The results revealed that: 1) The annual average air temperature UHI intensity from 2009 to 2012 was 0.9°C, the UHI intensity of the soil temperature at a depth of 0–320 cm was between −0.5°C and 0.2°C, and the air temperature UHI intensity was substantially stronger than that of the soil temperature. The surface (0 cm) and shallow (5 –40 cm) soil temperatures exhibited a “heat island effect,” the deep (80–320 cm) soil temperature exhibited a “cold island effect,” and the soil temperature at a depth of 40–80 cm was the “conversion horizon” of the two. 2) The air temperature UHI intensities during spring, summer, autumn, and winter were 1.1°C, 0.6°C, 0.7°C, and 1.3°C, respectively; the seasons exhibiting the strongest and weakest UHI intensities were winter and summer, respectively. During autumn, the soil temperature at different depths exhibited the cold island effect, with the intensity of the cold island effect at a depth of 320 cm being the strongest. During winter, the soil temperatures at the surface layer and above 80 cm predominantly exhibited the heat island effect, whereas those at a depth of 320 cm exhibited the cold island effect. The seasonal variation of the soil surface UHI intensity was consistent with that of the air temperature, and its physical mechanism exhibited similar properties. 3) The air temperature UHI intensity in each month was between 0.5°C and 1.6°C, with the strongest intensity observed during January and the weakest intensity observed during July and October. The soil temperatures at the surface layer and above 40 cm generally exhibited the heat island effect from January to July and December, and exhibited the cold island effect from August to November. The soil temperature below 80 cm exhibited the cold island effect for the majority of the year. 4) The UHI intensities of the annual and seasonal average air temperatures clearly exhibited diurnal variation characteristics; the annual and seasonal surface soil temperatures exhibited similar characteristics. However, with the increase in soil depth, the diurnal variation of soil temperature UHI intensity gradually weakened and finally transformed into the cold island effect.
A method for directly measuring carbon dioxide (CO2) emissions using a mobile sensor network in cities at fine spatial resolution was developed and tested. First, a compact, mobile system was built using an infrared gas analyzer combined with open-source hardware to control, georeference, and log measurements of CO2 mixing ratios on vehicles (car, bicycles). Second, two measurement campaigns, one in summer and one in winter (heating season) were carried out. Five mobile sensors were deployed within a 1 × 12. 7 km transect across the city of Vancouver, BC, Canada. The sensors were operated for 3.5 h on pre-defined routes to map CO2 mixing ratios at street level, which were then averaged to 100 × 100 m grid cells. The averaged CO2 mixing ratios of all grids in the study area were 417.9 ppm in summer and 442.5 ppm in winter. In both campaigns, mixing ratios were highest in the grid cells of the downtown core and along arterial roads and lowest in parks and well vegetated residential areas. Third, an aerodynamic resistance approach to calculating emissions was used to derive CO2 emissions from the gridded CO2 mixing ratio measurements in conjunction with mixing ratios and fluxes collected from a 28 m tall eddy-covariance tower located within the study area. These measured emissions showed a range of −12 to 226 CO2 ha⁻¹ h⁻¹ in summer and of −14 to 163 kg CO2 ha⁻¹ h⁻¹ in winter, with an average of 35.1 kg CO2 ha⁻¹ h⁻¹ (summer) and 25.9 kg CO2 ha⁻¹ h⁻¹ (winter). Fourth, an independent emissions inventory was developed for the study area using buildings energy simulations from a previous study and routinely available traffic counts. The emissions inventory for the same area averaged to 22.06 kg CO2 ha⁻¹ h⁻¹ (summer) and 28.76 kg CO2 ha⁻¹ h⁻¹ (winter) and was used to compare against the measured emissions from the mobile sensor network. The comparison on a grid-by-grid basis showed linearity between CO2 mixing ratios and the emissions inventory (R² = 0. 53 in summer and R² = 0. 47 in winter). Also, 87 % (summer) and 94 % (winter) of measured grid cells show a difference within ±1 order of magnitude, and 49 % (summer) and 69 % (winter) show an error of less than a factor 2. Although associated with considerable errors at the individual grid cell level, the study demonstrates a promising method of using a network of mobile sensors and an aerodynamic resistance approach to rapidly map greenhouse gases at high spatial resolution across cities. The method could be improved by longer measurements and a refined calculation of the aerodynamic resistance.
Any radiometer at a fixed location has a biased view when observing a
convoluted, three-dimensional surface such as an urban canopy. The goal of
this contribution is to determine the bias of various sensors views observing
a simple urban residential neighbourhood (nadir, oblique, hemispherical) over
a 24 hour cycle under clear weather conditions. The error in measuring a
longwave radiation flux density (L) and/or inferring surface temperatures
(T0) is quantified for different times over a diurnal cycle. Panoramic
time-sequential thermography (PTST) data were recorded by a thermal camera on
a hydraulic mast above a residential canyon in Vancouver, BC. The data set
resolved sub-facet temperature variability of all representative urban facets
in a 360° swath repetitively over a 24-hour cycle. This data set is
used along with computer graphics and vision techniques to project measured
fields of L for a given time and pixel onto texture sheets of a
three-dimensional urban surface model at a resolution of centimetres. The
resulting data set attributes L of each pixel on the texture sheets to
different urban facets and associates facet location, azimuth, slope,
material, and sky view factor. The texture sheets of L are used to
calculate the complete surface temperature (T0,C) and to simulate
the radiation in the field of view (FOV) of narrow and hemispheric
radiometers observing the same urban surface (in absence of emissivity and
atmospheric effects). The simulated directional (T0,d) and hemispheric
(T0,h) radiometric temperatures inferred from various biased views are
compared to T0,C. For a range of simulated off-nadir (φ) and
azimuth (Ω) angles, T0,d(φ,Ω) and T0,C differ
between −2.6 and +2.9 K over the course of the day. The effects of effective
anisotropy are highest in the daytime, particularly around sunrise and sunset
when different views can lead to differences in T0,d(φ,Ω) that
are as high as 3.5 K. For a sensor with a narrow FOV in the nadir of the
urban surface, T0,d(φ=0) differs from T0,C by +1.9 K (day)
and by −1.6 K (night).
Simulations of the FOV of hemispherical, downward-facing pyrgeometers at 270
positions show considerable variations in the measured L and inferred
hemispherical radiometeric temperature T0,h as a function of both
horizontal placement and height. The root mean squared error (RMSE) between
different horizontal positions in retrieving outgoing longwave emittance
L↑ decreased exponentially with height, and was 11.2, 6.3 and 2.0 W m−2 at 2, 3, and 5 times the mean building height zb.
Generally, above 3.5zb the horizontal positional error is less than the
typical accuracy of common pyrgeometers. The average T0,h over 24 h
determined from the hemispherical radiometer sufficiently above an urban
surface is in close agreement with the average T0,C. However, over
the course of the day, the difference between T0,h and T0,C
shows an RMSE of 1.7 K (9.4 W m−2) because the relative
contributions of facets within the projected FOV of a pyrgeometer do not
correspond to their fractions of the complete urban surface.
Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of
gases over an urban area are a direct way to improve and evaluate emissions
inventories, and, in turn, to better understand urban atmospheric chemistry
and the role that cities play in regional and global chemical cycles. As
part of the MCMA-2003 study, we demonstrated the feasibility of using eddy
covariance techniques to measure fluxes of selected volatile organic
compounds (VOCs) and CO2 from a residential district of Mexico City
(Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a
second flux measurement study was conducted in a different district of
Mexico City to corroborate the 2003 flux measurements, to expand the number
of species measured, and to obtain additional data for evaluation of the
local emissions inventory. Fluxes of CO2 and olefins were measured by
the conventional EC technique using an open path CO2 sensor and a Fast
Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of
toluene, benzene, methanol and C2-benzenes were measured using a
virtual disjunct EC method with a Proton Transfer Reaction Mass
Spectrometer. The flux measurements were analyzed in terms of diurnal
patterns and vehicular activity and were compared with the most recent
gridded local emissions inventory. In both studies, the results showed that
the urban surface of Mexico City is a net source of CO2 and VOCs with
significant contributions from vehicular traffic. Evaporative emissions from
commercial and other anthropogenic activities were significant sources of
toluene and methanol. The results show that the emissions inventory is in
reasonable agreement with measured olefin and CO2 fluxes, while
C2-benzenes and toluene emissions from evaporative sources are
overestimated in the inventory. It appears that methanol emissions from
mobile sources occur, but are not reported in the mobile emissions
inventory.
This study highlights the possibilities and constraints of determining instantaneous spatial surface radiation and land heat fluxes from satellite images in a heterogeneous urban area and its agricultural and natural surroundings. Net radiation was determined using ASTER satellite data and MODTRAN radiative transfer calculations. The soil heat flux was estimated with two empirical methods using radiative terms and vegetation indices. The turbulent heat fluxes finally were determined with the LUMPS (Local-Scale Urban Meteorological Parameterization Scheme) and the ARM (Aerodynamic Resistance Method) method. Results were compared to in situ measured ground data. The performance of the atmospheric correction was found to be crucial for the estimation of the radiation balance and thereafter the heat fluxes. The soil heat flux could be modeled satisfactorily by both of the applied approaches. The LUMPS method, for the turbulent fluxes, appeals by its simplicity. However, a correct spatial estimation of associated parameters could not always be achieved. The ARM method showed the better spatial results for the turbulent heat fluxes. In comparison with the in situ measurements however, the LUMPS approach rendered the better results than the ARM method.
Urban heat islands (UHI) are defined. The importance of distinguishing between different types is stressed and a simple classification scheme is forwarded. Emphasis in this paper is upon the heat island in the urban boundary layer (UBL) above roof-level (the UHIUBL).
The observed characteristics of the daytime and nocturnal UHIUBL are illustrated including the evolution of its thermal structure and the transition between the day and night régimes. Effects of weather controls on the UBL are mentioned.
The essential physics underlying the genesis of the daytime and nocturnal UHIUBL is outlined including radiative flux divergence, heating from below due to the altered surface energy balance, and heating from above due to entrainment.
UHIUBL effects on urban airflow and air pollution dispersion are numerous. Examples given include effects on thermal turbulence, atmospheric stability, convective structures, nocturnal inversions, mixed layer depth, local circulation systems, plume trajectories, intra- and inter-urban fumigation, humidity and rates of chemical reactions and biogenic emission.
A thermal property parameter for expressing the ground heat flux (cpλ; product of the heat capacity and the thermal conductivity) of urban complex terrain was estimated. The surface temperature time series was observed during nocturnal radiative cooling, and employed in the estimation. The surface temperature was obtained using the airborne-measured upward longwave radiation in order to consider the directional anisotropy of radiometric surface temperature. The effective thermal property parameter for a town-scale urban area was found to be two to four times larger than that of the surface material component. The explanation for this, shown by several model simulations and other radiometric observations, was total surface area increased due to urban canyon structure. The parameter cpλ on the town-scale was expressed by the canyon shape, and the cpλ of its component material.
A recent re-evaluation of urban heat island (UHI) studies has suggested that the urban effect may be expressed more meaningfully as a difference between Local Climate Zones (LCZ), defined as areas with characteristic dimensions of between one and several kilometers that have distinct effects on climate at both micro-and local-scales (city streets to neighborhoods), rather than adopting the traditional method of comparing urban and rural air temperatures. This paper reports on a UHI study in Dublin (Ireland) which maps the urban area into LCZ and uses these as a basis for carrying out a UHI study. The LCZ map for Dublin is derived using a widely available land use/cover map as a basis. A small network of in-situ stations is deployed into different LCZ across Dublin and additional mobile temperature traverses carried out to examine the thermal characteristics of LCZ following mixed weather during a 1 week period in August 2010. The results show LCZ with high impervious/building coverage were on average >4 °C warmer at night than LCZ with high pervious/vegetated coverage during conditions conducive to strong UHI development. The distinction in mean LCZ nocturnal temperature allows for the generation of a heat map across the entire urban area.
Distinguishes the Urban Canopy Layer (UCL) from the ground to roof level, from the Urban Boundary Layer (UBL) which extends to the height where urban influences are no longer perceptible. Methods to establish the energy balance include micrometeorological approaches and numerical models. Data are presented under the heading of radiation budget, anthropogenic heat release, subsurface (storage) heat flux, turbulent heat transfer, advection, and urban-rural energy balance differences. -K.Clayton
We present the turbulence spectra and cospectra derived from more than five years of eddy-covariance measurements at two urban sites in AdA(0), central Poland. The fast response wind velocity components were obtained using sonic anemometers placed on narrow masts at 37 and 42 m above ground level. The analysis follows Kaimal et al. (Q J R Meteorol Soc 98:563-589, 1972) who established the spectral and cospectral properties of turbulent flow in atmospheric surface layer on the basis of the Kansas experiment. Our results illustrate many features similar to those of Kaimal et al., but some differences are also observed. The velocity (co)spectra from AdA(0) show a clear inertial subrange with slope for spectra and slope for cospectra. We found that an appropriate stability function for the non-dimensional dissipation of turbulent kinetic energy calculated from spectra in the inertial subrange differs from that of Kaimal et al., and it can be satisfactorily estimated with the assumption of local equilibrium using standard functions for the non-dimensional shear production. A similar function for the cospectrum corresponds well to Kaimal et al. for unstable and weakly stable conditions. The (co)spectra normalized by their spectral values in the inertial subrange are in general similar to those of Kaimal et al., but they peak at lower frequencies in strongly stable conditions. Moreover, our results do not confirm the existence of a clear "excluded region" at low frequencies for the transition from stable to unstable conditions, for longitudinal and lateral wind components. The empirical models of Kaimal et al. with adjusted parameters fit well to the vertical velocity spectrum and the vertical momentum flux cospectrum. The same type of function should be used for longitudinal and lateral wind spectra because of their sharper peak than occurs for the Kansas data. Finally, it should be stressed that the above relationships are well-defined for averaged values. The results for individual 1-h periods are very scattered and can be significantly different from the generalized functions.
http://onlinelibrary.wiley.com/doi/10.1002/qj.2499/abstract
http://chubasco.niu.edu/pubs/Haberlie%20et%20al.%202015%20QJRMS.pdf
This study assesses the impact of urban land use on the climatological distribution of thunderstorm initiation occurrences in the humid subtropical region of the Southeast United States, which includes the Atlanta, Georgia metropolitan area. Initially, an automated technique is developed to extract the locations of isolated convective initiation (ICI) events from 17 years (1997-2013) of composite reflectivity radar data for the study area. Nearly 26,000 ICI points were detected during 85 warm-season months, providing the foundation for first long-term, systematic assessment of the influence of urban land use on thunderstorm development. Results reveal that ICI events occur more often over the urban area compared to its surrounding rural counterparts, confirming that anthropogenic-induced changes in land cover in moist tropical environments lead to more initiation events, resulting thunderstorms, and affiliated hazards over the developed area. The ICI risk for Atlanta is greatest during the late afternoon and early evening in July and August in synoptically benign conditions. Greater ICI counts downwind of Atlanta suggest that prevailing wind direction also influences the location of these events. Moreover, ICI occurrences over the city were significantly higher on weekdays compared to weekend days—a result that was not apparent in a rural control region located west of the city. This suggests that the weekly commuting cycle and associated aerosol levels of Atlanta may amplify ICI rates. The investigation provides a methodological framework for future studies that examine the effect of land use, land cover, and terrain discontinuities on the spatiotemporal character of ICI events.
Airborne measurements within the urban mixing layer (360 m) over Greater London are used to quantify CO2 emissions at the meso-scale. Daytime CO2 fluxes, calculated by the Integrative Mass Boundary Layer (IMBL) method, ranged from 46 to 104 mu mol CO2 m(-2) s(-1) for four days in October 2011. The day-to-day variability of IMBL fluxes is at the same order of magnitude as for surface eddy-covariance fluxes observed in central London. Compared to fluxes derived from emissions inventory, the IMBL method gives both lower (by -37%) and higher (by 19%) estimates. The sources of uncertainty of applying the IMBL method in urban areas are discussed and guidance for future studies is given.
AbstractThis study investigates interactive effects from the Beijing urban area on temperature, humidity, wind speed and direction, and precipitation by use of hourly automatic weather station data from June to August 2008-12. Results show the Beijing summer urban heat island (UHI) as a multi-center distribution (corresponding to underlying land-use features), with stronger nighttime than daytime values (averages of 1.7 vs. 0.8°C, respectively). Specific humidity was lower in urban Beijing than in surrounding non-urban areas, and this urban dry island is stronger during day than night (maximum of -2.4 vs. -1.9 g kg-1). Wind direction is affected by both a mountain- valley breeze circulation and by urbanization. Morning low-level flows converged into the strong UHI, but afternoon and evening southerly winds were bifurcated by an urban building-barrier induced divergence. Summer thunderstorms also thus bifurcated and bypassed the urban center, due to the building-barrier effect during both daytime and n
An outdoor summer study on thermal physiology along subjects' pathways was conducted in a Japanese city using a unique wearable measurement system that measures all the relevant thermal variables: ambient temperature, humidity, wind speed (U) and short/long-wave radiation (S and L), along with some physio-psychological parameters: skin temperature (T skin), pulse rate, subjective thermal sensation and state of body motion. U, S and L were measured using a globe anemo-radiometer adapted use with pedestrian subjects. The subjects were 26 healthy Japanese adults (14 males, 12 females) ranging from 23 to 74 years in age. Each subject wore a set of instruments that recorded individual microclimate and physiological responses along a designated pedestrian route that traversed various urban textures. The subjects experienced varying thermal environments that could not be represented by fixed-point routine observational data. S fluctuated significantly reflecting the mixture of sunlit/shade distributions within complex urban morphology. U was generally low within urban canyons due to drag by urban obstacles such as buildings but the subjects' movements enhanced convective heat exchanges with the atmosphere, leading to a drop in T skin. The amount of sweating increased as standard effective temperature (SET*) increased. A clear dependence of sweating on gender and body size was found; males sweated more than females; overweight subjects sweated more than standard/underweight subjects. T skin had a linear relationship with SET* and a similarly clear dependence on gender and body size differences. T skin of the higher-sweating groups was lower than that of the lower-sweating groups, reflecting differences in evaporative cooling by perspiration.
The influence of building geometry on the radiation terms of the surface energy balance is a principal reason for surface temperature differences between rural and urban areas. Methods exist to calculate the radiation balance in an urban area, but their validity across the range of urban geometries and materials has not been carefully considered. Here the exchange of diffuse radiation in an urban street canyon is investigated using a method incorporating all reflections of radiation. This exact solution is compared to two commonly used approximations that retain either no reflections, or just one reflection of radiation. The area-averaged net radiative flux density from the facets of the canyon decreases in magnitude monotonically as the canyon aspect ratio increases. The two approximate solutions possess unphysical differences from this monotonic decrease for high canyon aspect ratios or low material emissivities/high material albedos. The errors of the two approximate solutions are small for near blackbody materials and small canyon aspect ratios but can be an order of magnitude for intermediate material properties and deep street canyons. Urban street canyon models need to consider at least one reflection of radiation and multiple reflections are desirable for full applicability.
This study examines how urbanization affects the precipitation climatology in Tokyo, Japan. A unique aspect of this study is that an ensemble, regional climatological simulation approach is used with sensitivity experiments to reduce uncertainty arising from nonlinearity in the precipitation simulations. Another aspect is that the robustness of the precipitation response is tested with ‘‘stress response’’ simulations with increasing urban forcing. The results show that urbanization causes a robust increase in the amount of precipitation in the Tokyo metropolitan area and a reduction in the inland areas. These anomalies are statistically significant at the 95%
and 99%levels in some parts. There is no measureable change in the surrounding rural and ocean areas. These precipitation responses are attributed to an increase of surface sensible heat flux in Tokyo, which destabilizes the atmosphere and induces an anomalous surface low pressure pattern and the convergence of grid-scale horizontal moisture flux. The anomalous convergence of grid-scale horizontal moisture flux is a consequence of urbanization modifying the sea breeze.
Weather and climate changes caused by human activities (e.g., greenhouse gas emissions, deforestation, and urbanization) have received much attention because of their impacts on human lives as well as scientific interests. The detection, understanding, and future projection of weather and climate changes due to urbanization are important subjects in the discipline of urban meteorology and climatology. This article reviews urban impacts on precipitation. Observational studies of changes in convective phenomena over and around cities are reviewed, with focus on precipitation enhancement downwind of cities. The proposed causative factors (urban heat island, large surface roughness, and higher aerosol concentration) and mechanisms of urban-induced and/or urban-modified precipitation are then reviewed and discussed, with focus on downwind precipitation enhancement. A universal mechanism of urban-induced precipitation is made through a thorough literature review and is as follows. The urban heat island produces updrafts on the leeward or downwind side of cities, and the urban heat island-induced updrafts initiate moist convection under favorable thermodynamic conditions, thus leading to surface precipitation. Surface precipitation is likely to further increase under higher aerosol concentrations if the air humidity is high and deep and strong convection occurs. It is not likely that larger urban surface roughness plays a major role in urbaninduced precipitation. Larger urban surface roughness can, however, disrupt or bifurcate precipitating convective systems formed outside cities while passing over the cities. Such urban-modified precipitating systems can either increase or decrease precipitation over and/or downwind of cities. Much effort is needed for in-depth or new understanding of urban precipitation anomalies, which includes local and regional modeling studies using advanced numerical models and analysis studies of long-term radar data.
Based on field data from 10 USA cities and national urban tree cover data, it is estimated that urban trees in the coterminous USA currently store 700 million tonnes of carbon ($14,300 million value) with a gross carbon sequestration rate of 22.8 million tC/yr ($460 million/year). Carbon storage within cities ranges from 1.2 million tC in New York, NY, to 19,300 tC in Jersey City, NJ. Regions with the greatest proportion of urban land are the Northeast (8.5%) and the southeast (7.1%). Urban forests in the north central, northeast, south central and southeast regions of the USA store and sequester the most carbon, with average carbon storage per hectare greatest in southeast, north central, northeast and Pacific northwest regions, respectively. The national average urban forest carbon storage density is 25.1 tC/ha, compared with 53.5 tC/ha in forest stands. These data can be used to help assess the actual and potential role of urban forests in reducing atmospheric carbon dioxide, a dominant greenhouse gas.
Recent advances in thermal infrared remote sensing include the increased availability of airborne hyperspectral imagers (such as the Hyperspectral Thermal Emission Spectrometer, HyTES, or the Telops HyperCam and the Specim aisaOWL), and it is planned that an increased number spectral bands in the long-wave infrared (LWIR) region will soon be measured from space at reasonably high spatial resolution (by imagers such as HyspIRI). Detailed LWIR emissivity spectra are required to best interpret the observations from such systems. This includes the highly heterogeneous urban environment, whose construction materials are not yet particularly well represented in spectral libraries. Here, we present a new online spectral library of urban construction materials including LWIR emissivity spectra of 74 samples of impervious surfaces derived using measurements made by a portable Fourier Transform InfraRed (FTIR) spectrometer. FTIR emissivity measurements need to be carefully made, else they are prone to a series of errors relating to instrumental setup and radiometric calibration, which here relies on external blackbody sources. The performance of the laboratory-based emissivity measurement approach applied here, that in future can also be deployed in the field (e.g. to examine urban materials in situ), is evaluated herein. Our spectral library also contains matching short-wave (VIS–SWIR) reflectance spectra observed for each urban sample. This allows us to examine which characteristic (LWIR and) spectral signatures may in future best allow for the identification and discrimination of the various urban construction materials, that often overlap with respect to their chemical/mineralogical constituents. Hyperspectral or even strongly multi-spectral LWIR information appears especially useful, given that many urban materials are composed of minerals exhibiting notable reststrahlen/absorption effects in this spectral region. The final spectra and interpretations are included in the London Urban Micromet data Archive (LUMA; http://LondonClimate.info/LUMA/SLUM.html).
Detailed eddy covariance measurements of radiation, energy and carbon dioxide fluxes over a residential neighbourhood of Singapore are presented. The measurements cover a period of ∼7years and represent the longest set of flux data reported for a tropical city. Owing to its equatorial location, the observed radiation fluxes are uniformly high throughout the year. Annual changes in climate, energy fluxes and carbon dioxide exchange are therefore much less than observed in cities located outside the Tropics. The energy balance partitioning is nevertheless similar to that reported for subtropical and mid-latitude suburban sites. Across the entire study period and all weather conditions 53.6% of net radiation (3.222GJm⁻²year⁻¹) is partitioned into sensible and 39.4% into latent heat, respectively, resulting in a long-term daily Bowen ratio of ∼1.4. Significant variability exists in net radiation and sensible heat flux using a classification based on clouds and rainfall. Carbon dioxide fluxes are generally positive throughout the day with morning and evening peaks related to maxima in traffic volume separating lower day- from higher nighttime fluxes. Unlike in many other comparable suburban studies, net fluxes are generally higher during night- compared to daytime. The largest daily fluxes and most pronounced diurnal variability coincide with seasons when the flux footprint includes the highest proportion of vegetation, suggesting an important role for daytime sequestration and nighttime respiration to control the diurnal and seasonal variation. Carbon dioxide fluxes change little across the year given the absence of a heating season with an annual total mass flux of 6368MgCO2km⁻²year⁻¹. Singapore provides a unique climatic context, and the present long-term study is expected to add robust statistics from the understudied (sub)tropical region to the global data set of urban energy and carbon dioxide fluxes, which is dominated by work conducted in mid- and high latitudes.
Major reviews of urban effects on local climate, extending from Kratzer in 1937 through to Landsberg in 1981, have dealt primarily with radiation, temperature, wind, and air quality. To a much lesser extent they have examined moisture-related elements including humidity, cloud, precipitation, and storminess. Selecting air temperature to represent the former group and precipitation amount to represent the latter, the author asserts that, because of the intrinsic physical differences between them, there are necessarily important differences in the methods to be used for their proper observation, analysis, presentation, and interpretation pertaining to urban effects. The principal differences are based in the fact that temperature is continuous in both time and space, whereas precipitation is continuous in neither. The author maintains that because of these differences, urban climatologists have had much greater success in specifying and explaining urban effects on temperature than on precipitation amount. Further, he makes the case that, lack of recognition that methods used for the study of urban effects on temperature are too often inappropriate for study of urban effects on precipitation amount, has led to a state of affairs where there remains basic uncertainty about the specification of urban effects on precipitation amount, and even greater uncertainty about their explanation. In making that case, the author includes 1) an historical perspective, 2) a critical evaluation of methods, 3) an overview of the status of urban precipitation climatology, and 4) recommendations concerning future research.
The history of numerical modeling of the effect of aerosols on clouds dates back at least 50 years to the work of Howell (1949) and Mordy (1959), who considered the growth of a population of aerosol particles in a rising parcel of air. Models such as these addressed the effects of both aerosol and dynamical parameters (i.e. updraft velocity) on the number and size distribution of cloud droplets. To this day similar models are in wide use to examine the effects of aerosol composition and atmospheric trace gases on droplet activation (e.g. Kulmala et al. 1993; Ghan et al. 1997; Feingold and Chuang 2002; Nenes et al. 2002).
Urbanization is an agent of change at local, regional, and global-scales. The conversion of a landscape to urban land cover causes large changes to the local and regional energy, carbon, and water balances; as well as air quality and climate. At regional to global-scales, the flows of materials (water, carbon, pollutants, etc.) and energy are modified by the new ecosystem; they are imported and consumed within the city and the resulting waste emitted and exported to the surroundings. Urban areas therefore have a much greater environmental impact than the 2% of the total global land area they occupy. The clearest demonstration of their global impact, however, is the significant contribution that cities make to anthropogenic climate change through large net emissions of Green House Gas. This is why understanding the interactions between the urban environment and global climate change is so important.
We are living in a century of rapid urbanisation. The United Nations forecasts that by the year 2025, 60% of the world???s population will be living in urban areas, compared to 29% in 1950. The 50% mark will be reached between the years 2000 and 2010. In 2025, more than a dozen cities will have over 20 million inhabitants, and some will have over 30 million. 23 of the 25 biggest urban conglomerations on the planet will be in Africa, Asia and Latin America, rather than in Europe or North America.
A review of the physical characteristics of sulfur-containing aerosols, with respect to size distribution of the physical distributions, sulfur distributions, distribution modal characteristics, nuclei formation rates, aerosol growth characteristics, and in situ measurement, has been made. Physical size distributions can be characterized well by a trimodal model consisting of three additive lognormal distributions. When atmospheric physical aerosol size distributions are characterized by the trimodal model, the following typical modal parameters are observed: 1. 1. Nuclei mode - geometric mean size by volume, DGVa from 0.015 to 0.04 μm, σgn, = 1.6, nuclei mode volumes from 0.0005 over the remote oceans to 9μm3 cm-3 on an urban freeway. 2. 2. Accumulation mode - geometric mean size by volume, DGVa, from 0.15 to 0.5μm, σgn = 1.6-2.2 and mode volume concentrations from 1 for very clean marine or continental backgrounds to as high as 300μm3cm-3 under very polluted conditions in urban areas. 3. 3. Coarse panicle mode - geometric mean size by volume, DGVa, from 5 to 30 μm, σgn, = 2-3. and mode volume concentrations from 2 to 1000 μm3 cm-3. It has also been concluded that the fine particles (Dp < 2 μm) are essentially independent in formation, transformation and removal from the coarse particles (Dp> 2μm). Modal characterization of impactor-measured sulfate size distributions from the literature shows that the sulfate is nearly all in the accumulation mode and has the same size distribution as the physical accumulation mode distribution. Average sulfate aerodynamic geometric mean dia. was found to be 0.48 ± 0.1 μm (0.37 ± 0.1 μm vol. dia). and ν = 2.00 ± 0.29. Concentrations range from a low of about 0.04 μg m -3 over the remote oceans to over 80μm-3 under polluted conditions over the continents. Review of the data on nucleation in smog chambers and in the atmosphere suggests that when SO2 is present, SO2-to-aerosol conversion dominates the Aitken nuclei count and, indirectly, through coagulation and condensation, the accumulation mode size and concentration. There are indications that nucleation is ubiquitous in the atmosphere, ranging from values as low as 2 cm-3 h-1' over the clean remote oceans to a high of 6 × 106 cm -3 h-1' in a power plant plume under sunny conditions. There is considerable theoretical and experimental evidence that even if most of the mass for the condensational growth of the accumulation mode comes from hydrocarbon conversion, sulfur conversion provides most of the nuclei.
A two-dimensional, non-steady model of the flow over an infinitely wide, warm, rough city is presented. The model consists of two layers, a lower analytical constant-flux layer, and an upper finite-difference transition layer, in which the vorticity and heat conduction equations are solved. The atmosphere is assumed to be Boussinesq, hydrostatic and slab symmetric, while all motions are assumed to be adiabatic. Finite-difference solutions are obtained over a variable, interlaced grid, with the use of a time-splitting technique, in conjunction with the donor cell method of differencing the advection terms. Simulations were carried out reproducing the daytime flow of a neutral atmosphere over a rough city, and the nighttime flow of stable atmosphere over a rough, warm city. Comparisons are presented to show that the model is capable of reproducing many of the observed characteristics of the urban boundary layer.
Investigations of the nocturnal temperature and wind structure of the planetary boundary layer over a city were conducted in the Cincinnati, Ohio, metropolitan area. Temperatures near the surface were obtained by means of automobile traverses across the city, the vertical distributions of temperature were measured at several sites with a helicopter, and wind velocities were derived from pilot balloon observations.
Results of the investigations demonstrated a pronounced modification of the vertical temperature structure as air with a rural history traversed the city. The vertical extent of the modification, referred to herein as the “urban boundary layer,” gradually increased with downwind distance over the urban area. Beyond the downwind side of the urban area, relatively unstable air was found aloft over a stable surface layer, suggesting a layer of outflowing urban air aloft that is called the “urban heat plume.”
When a strong inversion existed in the planetary boundary layer upwind from the city, the urban boundary layer extended 150 to 300 ft above the surface. A superadiabatic lapse rate was observed within the urban boundary layer in the central business district and an isothermal lapse rate or weak inversion in the downwind suburban areas. A strong inversion, similar to that of the upwind rural environment, was maintained above the urban boundary layer.
This chapter was originally published in the book Climate Vulnerability. The copy attached is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research, and educational use. This includes without limitation use in instruction at your institution, distribution to specific colleagues, and providing a copy to your institution's administrator. All other uses, reproduction and distribution, including without limitation commercial reprints, selling or licensing copies or access, or posting on open internet sites, your personal or institution's website or repository, are prohibited. For exceptions, permission may be sought for such use through Elsevier's permissions site at: http://www.elsevier.com/locate/permissionusematerial From Shepherd, J., 2013: Impacts of Urbanization on Precipitation and Storms: Physical Insights and Vulnerabilities. In: Climate Vulnerability: Understanding and Addressing Threats to Essential Resources. pp. 109–125
Rapid decrease in relative humidity at urban climatological stations in Japan during 1950's and 1960's abruptly ended around 1970. Since then the annual mean of relative humidity has remained at almost the same level excepting interannual variation. The recent trends are even suggestive of its increase for data at stations in big cities such as Tokyo and Osaka. It is important to note that apparent decreasing trends prevail recent years at stations in rural areas instead. The differences between urban climatological stations with near-by rural stations in both relative humidity and vapor pressure are decreasing recent 10∼20 years. It is shown that during the rapid drying period both the effects of water vapor pressure decrease and temperature rise worked effectively. The recent decrease in urban-rural difference due not only to drying of rural areas noted above but also to increase in the water vapour contents in the urban atmosphere, latter by human activities. At the present urban-rural difference in relative humidity at Tokyo and Osaka are largely attributable to urban warming. It is also demonstrated that urban drying reduces discomfort from hot and humid climate in summer at large cities west of Tokyo.
Solar access has a critical influence on human thermal comfort. In shaded areas, direct shortwave
radiation fluxes decrease and a cooling effect is produced. The percentage and position of shaded areas
in an open space depend on sun position and urban morphology, so they change during the day,
affecting attendance distribution over time. The study assessed the relationship between daily shading
patterns, attendance and thermal comfort during summer at San Silvestro square in Rome, Italy. Field
investigations were conducted on 1st and 2nd August 2014, including meteorological measurements and
unobtrusive observations. The assessment of thermal comfort was based on the Physiologically
Equivalent Temperature (PET), calculated using the RayMan model. The majority of visitors at San
Silvestro square sought shaded locations when sitting, resulting in a variation of attendance throughout
the day. The attendance in unshaded location passed from 0 – 2 people at 11:00 to 2 – 10 at 12:00,
whereas the attendance in shaded locations had a minimum of 0 – 4 at 12:00 and a maximum of 52 –
94 at 18:00. This preference was strongly correlated with thermal comfort analysis, as PET values
were significantly lower in shaded areas. The minimum difference in the median of PET from shaded
and unshaded locations was 2 °C at 18:00 and the maximum difference was 7 °C at 11:00. The main
findings of this study highlight the importance of considering daily shading pattern when renovating
open spaces in Mediterranean climate and can be used as reference for future renovations.
This paper demonstrates the relation between the heat island intensity and city size indices/urban canopy characteristics. This is accomplished by analyzing the data at 6 settlements on the Nagano basin, Japan, whose population ranges from 3,300 to 360,000. The results show that heat island intensities on fine nights and cloudy nights, ΔTu-r are related to the logarithm of the settlement population P, which has one of the highest correlations to the heat island intensity in a city size index such as city area, DID (Densely Inhabitant District) area, DID population and so on. The gradient of regression between ATu-r and P is larger on fine nights than on cloudy nights, and is larger on nights with weak wind than on nights with strong wind. The correlation of population with maximum heat island intensity is remarkably high for Japanese settlements.
Some results from a series of measuring trips by car are discussed. The measuring trips were undertaken at three-hourly intervals. For more comprehensive mean value calculations, fixed stations with recording instruments have been used. The monthly mean temperature differences for every other hour of the 24-hour period between the various stations have been studied. The thawing after a snowfall has been measured on the ground and evaluated from aerial photographs.
Local heterogeneity of CO 2 sources and sinks is a key factor for the variability of carbon dioxide flux ( F C ) in urban areas. Information on the urban structure around a site, especially the related emission characteristics, is thus of great importance to the understanding of observed F C . Strong spatially confined sources like major roads inhibit a direct correlation of F C to area‐averaged features of the urban structure and may lead to a heavily biased signal.
Four years of F C measured at Basel Aeschenplatz, Switzerland, are analysed with respect to the controlling factors and the cause for variability on different time scales. The source area is segregated into equal sectors to address heterogeneous emission patterns. Residential areas to the east are bordered by business areas and major roads to the west, which leads to a fundamental dependence of F C on wind direction. Besides, its diurnal course is explainable with traffic emissions while its annual course follows heating‐related combustion emissions. Vegetation fraction is rather considered to be an indicator for urban land use types (residential/business) and the attributable emission characteristics than to be a measure for biological sink effects. Inter‐annual variability occurs as a result of anomalies in wind direction patterns or air temperature. Average yearly F C is 16.4 µmol m –2 s –1 with slight variations (±0.55 µmol m –2 s –1 ) over the 4 years. It likely originates from an average of 70% traffic and 30% heating‐related emissions with significant sectoral differences.
As a continuous measure for the emissions of each sector, the expected CO 2 flux ( eF C ) per sector is introduced, leading to an enhanced comparability. Relating sectoral eF C instead of F C to urban surface fractions of buildings and vegetation results in a better agreement (also with data from other studies).
Temperature observations were done at Ogaki city (pop. 75, 000) in Nobi Plain in Central Honshu and at Kumagaya city (pop. 94, 000) in Kanto Plain. Both of them are located in the middle of the flat alluvial plains and surrounded by extensive paddies. The greater parts of their built-up areas are occuppied by one or two story wooden houses. There are only a few tall concrete buildings in their central areas. Their main roads are paved with asphalt and concrete. Typical distribution patterns of city temperature were observed as were shown in the following figures. The observation were done using the elctric thermometers of thermistor type which we made. The thermometers was mounted on the front bumper of an automobile at about two meters above the ground. Several hundreds observations were made using a technique of moving observation at both cities. At the same times, about ten quick-winding thermographs of our types were installed in and around cities. Fig. 4 shows an isopleth of the temperature variation in thirty minuites intervals at a calm day in Ogaki. The densely populated areas show small variations and the changes occur a little later than the countrysides. Figs. 1, 2, and 3 show typical distribution patterns of temperature in Ogaki at different weather conditions. The pattern of the isotherm distribution shows a strong similarity with the distribution of house density in the city as is shown in fig. 1; Higher temperatures were observed at densely built-up areas, and big temperature-gradients were recognized at the surroundings of the cities. Also temperatures on paved roads seemed to be warmer than those on unpaved roads. Relations between temperature distribution and house density of 200 m square were analyzed on both cities, We could find that 10% increase in house density corresponded to 0.2-0.3°C temperature increase as were shown in Fig. 5. However, the -areas covered by two story houses had 0.2-0.4°C higher temperatures than other areas. These values seemed to be effected by weather conditions remarkably, especially by wind speed. When wind is strong, the values of temperature increase decreases strongly.
In the previous paper, the author analyzed the detailed distribution of temperature in and around Kumagaya City, situated in the central part of Kantô Plain, concerning various weather conditions (Geographical Review of Japan, Vol. 37, No. 5, pp. 243-254). Relationship between city temperature and meteorological factors suggests that the cause of city temperature of a local city in Japan is seen in the difference of radiation balance between urban areas and surroundings and especially construction materials of a city plays an important role in deciding city temperature. Further considerations on the cause of city temperature were attempted in this paper. The comprehensive book about city climate by A. Kratzer shows that the following three factors are important as the causes of city temperature: artificial heat produced in urban areas, pollution of city air and effect of construction materials of a city. In the case of this paper, however, it seems that the amount of artificial heat is relatively small and pollution of city air is unimportant, because the city size is small and there are very few factories in the city which consume a large amount of coal. Especially in summer season, these two factors are negligible. Difference of radiation balanced between the urban area and the surroundings affects on the city temperature in two ways. Those are the physical properties of constrution materials of the city concerning heat balance and the unevennss of the surface coverage of the city influencing heat transfer. Physical nature of construction materials of the city decides surface temperature of the earth. Nocturnal cooling of surface temperature of the earth is represented by Brunt's formula in accuracy of first approximation. The surface of the earth (T) is given by _??_ wher T0; surface temperature of the earth at the time of sunset, R; nocturnal radiation from the surface of the earth, ρ; density of ground, c; specific heat of ground, κ; specific conductivity of heat of ground. Assuming that the nocturnal radiation from the ground to the air (R) does not vary with time, T is decided by 1/cρ√κ. This formula was applied to the surface temperature of various construction materials of the city and then evaluation of nocturnal cooling was attempted as follows. Firstly, areas of roads, houses, grounds and so on in each 50m-meshed square were measured by using the map of 1/3000 scale and the relative portion of their respective areas for each section was calculated. Secondly, 1/cρ√κ in each section was computd. Values of 1/cρ√κ of each material are given in Table 1. (Concrete, asphalt, roofing the and soil are listed from above to below.) Then, this value in each section was converted into value of 1/cρ√κ, in 200 mmeshed setion. The result is shown in Figure 2. The close relationship between temperature in the urban area and the value of 1/cρ√κ is shown in Figure 3. This figure shows that both physical properties of construction materials and unevenness of the city play important roles in deciding city temperature. Unevenness of surface coverage in an urban area results in the decrease of nocturnal radiation and wind velocity. Consequently, decrease of noctvrnal radiation accelerates decreasing of nocturnal cooling in an urban area and drop of wind speed in an urban area promotes decreasing of heat tranfer from below to above in city air. As a result, temperature in an urban area becomes higher than in the surroundings.
There are few studies on the microclimate and human comfort of urban areas in hot dry climates. This study investigates the influence of urban geometry on outdoor thermal comfort by comparing an extremely deep and a shallow street canyon in Fez, Morocco. Continuous measurements during the hot summer and cool winter seasons show that, by day, the deep canyon was considerably cooler than the shallow one. In summer, the maximum difference was on average 6K and as great as 10K during the hottest days. Assessment of thermal comfort using the PET index suggests that, in summer, the deep canyon is fairly comfortable whereas the shallow is extremely uncomfortable. However, during winter, the shallow canyon is the more comfortable as solar access is possible. The results indicate that, in hot dry climates a compact urban design with very deep canyons is preferable. However, if there is a cold season as in Fez, the urban design should include some wider streets or open spaces or both to provide solar access.
Pavement-watering as a technique of cooling dense urban areas and reducing the urban heat island effect has been studied since the 1990’s. The method is currently considered as a potential tool for and climate change adaptation against increasing heat wave intensity and frequency. However, although water consumption necessary to implement this technique is an important aspect for decision makers, optimization of possible watering methods has only rarely been conducted. An analysis of pavement heat flux at a depth of 5 cm and solar irradiance measurements is proposed to attempt to optimize the watering period, cycle frequency and water consumption rate of a pavement-watering method applied in Paris over the summer of 2013. While fine-tuning of the frequency can be conducted on the basis of pavement heat flux observations, the watering rate requires a heat transfer analysis based on a relation established between pavement heat flux and solar irradiance during pavement insolation. From this, it was found that watering conducted during pavement insolation could be optimized to 30-minute cycles and water consumption could be reduced by more than 80% while reducing the cooling effect by less than 13%.
[1] Using seven summer-seasons (1997–2003) of NEXRAD data (over 46,000 volumes), coincident climatologies of cloud-to-ground (CG) lightning flash densities and radar-derived, column integrated precipitation ice mass (IM) were developed, extending global studies of IM and lightning to more regional and cell scales around Houston, TX. Results indicate that local maximums in CG lightning were indeed accompanied by peaks in IM. Extending previous global findings to cell-scales, we establish a link between a storm's ability to generate enhanced concentrations of mixed-phase IM, and its ability to generate lightning. Relative to the documented CG lightning “anomaly” over Houston, these results imply that unique aspects of the Houston urban area must first generate an anomaly in convective intensity and precipitation ice, thereby generating an anomaly in lightning; causal hypotheses must be capable of explaining either increased frequency and/or intensity of convection, and then relating these to the enhancement of IM and lightning production.
The village of Barrow, Alaska, is the northernmost settlement in the USA and the largest native community in the Arctic. The population has grown from about 300 residents in 1900 to more than 4600 in 2000. In recent decades, a general increase of mean annual and mean winter air temperature has been recorded near the centre of the village, and a concurrent trend of progressively earlier snowmelt in the village has been documented. Satellite observations and data from a nearby climate observatory indicate a corresponding but much weaker snowmelt trend in the surrounding regions of relatively undisturbed tundra. Because the region is underlain by ice-rich permafrost, there is concern that early snowmelt will increase the thickness of the thawed layer in summer and threaten the structural stability of roads, buildings, and pipelines. Here, we demonstrate the existence of a strong urban heat island (UHI) during winter. Data loggers (54) were installed in the ∼150 km2 study area to monitor hourly air and soil temperature, and daily spatial averages were calculated using the six or seven warmest and coldest sites. During winter (December 2001–March 2002), the urban area averaged 2.2 °C warmer than the hinterland. The strength of the UHI increased as the wind velocity decreased, reaching an average value of 3.2 °C under calm (<2 m s−1) conditions and maximum single-day magnitude of 6 °C. UHI magnitude generally increased with decreasing air temperature in winter, reflecting the input of anthropogenic heat to maintain interior building temperatures. On a daily basis, the UHI reached its peak intensity in the late evening and early morning. There was a strong positive relation between monthly UHI magnitude and natural gas production/use. Integrated over the period September–May, there was a 9% reduction in accumulated freezing degree days in the urban area. The evidence suggests that urbanization has contributed to early snowmelt in the village. Copyright
The first measurements of the energy balance fluxes of a dry, densely built-up, central city site are presented. Direct observation of the net radiation, sensible and latent heat flux densities above roof-top in the old city district of Mexico City allow the heat storage flux density to be found by residual. The most important finding is that during daytime, when evaporation is very small (< 4% of net radiation), and therefore sensible heat uses dominate (Bowen ratio > 8), the uptake of heat by the buildings and substrate is so large (58%) that convective heating of the atmosphere is reduced to a smaller role than expected (38%), The nocturnal release of heat from storage is equal to or larger than the net radiation and sufficient to maintain an upward convective heat flux throughout most nights. It is important to see if this pattern is repeated at other central city, or dry urban sites, or whether it is only found in districts dominated by massive stone structures. These findings have implications for the height of the urban mixing layer and the magnitude of the urban heat island.
Interpretation of tower-based eddy covariance (EC) carbon dioxide flux (F C ) measurements in urban areas is challenging because of the location bias of EC instruments. This bias results from EC point measurements taken above a complex CO2 source/sink surface that is spatially heterogeneous at scales approaching or exceeding those of the turbulent flux source areas. This makes it difficult to accomplish traditional measurement objectives such as calculating spatially unbiased ecosystem-wide cumulative F C totals or objectively comparing F C during different environmental conditions (e.g., day vs. night or seasonal differences). This study uses a multiyear F C dataset measured over a residential area of Vancouver, BC, Canada from a 30-m flux tower in close proximity to a busy traffic intersection on one side. The F C measurements are analyzed using surface geospatial data and turbulent flux source area models to exploit location bias to develop methods to statistically model individual emissions and uptake processes in terms of environmental controls and surface land cover. The empirical relations between controls and measured F C are used to spatially and temporally downscale individual CO2 emissions/uptake processes that are then used to create high-resolution maps (20 m) and calculate ecosystem-wide F C at temporal resolutions of 30 min to 1 year. At this site, the modeled ecosystem-wide annual net F C total is calculated as 6.42 kg C m-2 year-1 with traffic emissions estimated to account for 68.8 % of the total net emissions. Building sources contribute 27.9 %, respiration from soil and vegetation is 5.5 %, respiration from humans 5.0 %, and photosynthesis offsets are -7.2 % of the annual net total. The statistical models developed here are then tested by direct comparison to independent EC measurements using land cover scalings derived from 30-min source area models. Results are also scaled to ecosystem-averaged land cover to compare results to independent emissions/uptake models.
Variation of the energy budget components of a dry asphalt surface over an annual cycle is discussed based on the analysis of data collected from a micrometeorological road station near Vienna, in Austria. Net radiation (RN) and ground heat flux (G) are directly measured. Sensible heat flux (H) for dry surface conditions is estimated as a residual of the surface energy balance. Throughout the year, ground heat flux is found to be of larger magnitude than that of the sensible heat flux. The partitioning of net radiation into ground and sensible heat fluxes are studied. Variation of G (and H) with RN showed hysteresis loop behaviour with anti-clockwise cycle (clockwise for H) during cooler periods and clockwise cycle (anti-clockwise for H) during warm periods. The coefficients of time-dependent Camuffo and Bernadi formulations relating the net radiation with the heat fluxes are estimated for different periods of the year.