To build healthy, resilient, and climate‐responsive cities, planners need ways to understand the local complexities of urban thermal climates. To assist in meeting this need, this study employs the ...simple classification of “local climate zones” (LCZs) to conduct a spatiotemporal thermal climatic analysis of the Toulouse Metropolitan Region (France) under warm and dry summer conditions. Simulations are performed using the mesoscale atmospheric model Méso‐NH. These simulations provide a city‐wide spatial coverage of 2‐m air temperature (T2M), mean radiant temperature (MRT), and Universal Thermal Climate Index (UTCI). Model parameters describing the urban morphology are initialized based on administrative databases and independent of LCZ maps, which allows for an evaluation of whether the distributions of the modelled thermal climatic parameters will differ between LCZs. The results show that different LCZs possess significantly different distributions of T2M and MRT, confirming the suitability of the LCZ scheme for discerning the thermal environment of Toulouse. Compact urban settings (LCZ 1/2/3) show the highest T2M throughout the day and a nocturnal temperature difference of up to 2.8 K compared to rural settings. The MRT of LCZ 1/2/3 in the late afternoon (1700–2000 LST (UTC + 2)) can be as much as 6.3 K lower than it is for LCZs with open settings due to shading by dense urban structures. Additional analysis reveals that the intra‐LCZ variabilities of T2M and MRT may be explained by the distance to the city centre. Finally, the thermal stress in different LCZs is assessed with the modelled UTCI. Among the built LCZs, the probability of strong heat stress is the highest for open high/mid‐rise (LCZ 4/5) and lowest for sparsely built (LCZ 9) and open low‐rise (LCZ 6) settings. For land cover type LCZs, dense trees (LCZ A) are the most favourable for daytime outdoor human thermal comfort.
Distributions of air temperature at 2 m above ground and mean radiant temperature for different local climate zones (LCZs) in Toulouse Metropolitan Region (southern France). Thermal climatic parameters are taken from simulations with the mesoscale atmospheric model Méso‐NH for calm and sunny summer days. Distinct thermal characteristics are identified for different LCZs, notably the warmer built‐up LCZs during the night and the lower mean radiant temperatures for compact LCZ 1/2/3 and dense trees (LCZ A) due to shading in the day.
The urban climate map (UCMap) system has been widely applied in climate-friendly urban design. To facilitate accurate and effective UCMap construction, this study combines the urban energy balance ...calculation model (UDC) and local climate zone (LCZ) parameterization to obtain dynamic block-scale urban climatic parameters. The study area is the Higher Education Mega Center (HEMC) of Guangzhou, and a block-based LCZ classification methodology is proposed to generate an LCZ map of the HEMC. Then a framework is established by integrating the LCZ parameterization and UDC model to obtain a spatiotemporal UCMap atlas of the HEMC. The results show that the overall average local-scale urban heat island intensity (LUHII) and urban wet island intensity (LUWII) vary by 4.99 °C and 3.87 g/kg, respectively, over 24 h. Regarding the spatial distributions, the average LUHII and LUWII reach maximum values of 6.6 °C and 1.3 g/kg, respectively, within the HEMC. Additionally, correlation analysis of the physical property parameters and simulated climatic parameters shows that among the physical parameters, both the sky view factor and pervious surface fraction (PSF) have significant positive effects on the LUHII, whereas only the PSF has a positive effect on the LUWII. Furthermore, quantitative equations describing these relationships are derived, and climate problem zones are defined in terms of temperature and humidity. Identification of these climate problem zones within the HEMC enables appropriate optimization measures to support climate-friendly urban planning.
•A block-based LCZs classification methodology is proposed.•The LCZs parameterization and UDC model is integrated into UCMap making.•Hourly thermal and humid UCMap atlas are displayed.•Spatial morphology optimization strategy for the climate problem zones is presented.
Rapid and uncontrolled urbanization in tropical Africa is increasingly leading to unprecedented socio-economical and environmental challenges in cities, particularly urban heat and climate change. ...The latter calls for a better representation of tropical African cities’ properties relevant for urban climate studies. Here, we demonstrate the possibility of collecting urban canopy parameters during a field campaign in the boreal summer months of 2018 for deriving a Local Climate Zone (LCZ) map and for improving the physical representation of climate-relevant urban morphological, thermal and radiative characteristics. The comparison of the resulting field-derived LCZ map with an existing map obtained from the World Urban Data and Access Portal Tool framework shows large differences. In particular, our map results in more vegetated open low-rise classes. In addition, site-specific fieldwork-derived urban characteristics are compared against the LCZ universal parameters. The latter shows that our fieldwork adds important information to the universal parameters by more specifically considering the presence of corrugated metal in the city of Kampala. This material is a typical roofing material found in densely built environments and informal settlements. It leads to lower thermal emissivity but higher thermal conductivity and capacity of buildings. To illustrate the importance of site-specific urban parameters, the newly derived site-specific urban characteristics are used as input fields to an urban parametrization scheme embedded in the regional climate model COSMO-CLM. This implementations decreases the surface temperature bias from 5.34 to 3.97 K. Based on our results, we recommend future research on tropical African cities to focus on a detailed representation of cities, with particular attention to impervious surface fraction and building materials.
Significance Many case studies of specific cities have investigated factors that contribute to urban energy use and greenhouse-gas emissions. The analysis in this study is based on data from 274 ...cities and three global datasets and provides a typology of urban attributes of energy use. The results highlight that appropriate policies addressing urban climate change mitigation differ with type of city. A global urbanization wedge, corresponding in particular to energy-efficient urbanization in Asia, might reduce urban energy use by more than 25%, compared with a business-as-usual scenario.
The aggregate potential for urban mitigation of global climate change is insufficiently understood. Our analysis, using a dataset of 274 cities representing all city sizes and regions worldwide, demonstrates that economic activity, transport costs, geographic factors, and urban form explain 37% of urban direct energy use and 88% of urban transport energy use. If current trends in urban expansion continue, urban energy use will increase more than threefold, from 240 EJ in 2005 to 730 EJ in 2050. Our model shows that urban planning and transport policies can limit the future increase in urban energy use to 540 EJ in 2050 and contribute to mitigating climate change. However, effective policies for reducing urban greenhouse gas emissions differ with city type. The results show that, for affluent and mature cities, higher gasoline prices combined with compact urban form can result in savings in both residential and transport energy use. In contrast, for developing-country cities with emerging or nascent infrastructures, compact urban form, and transport planning can encourage higher population densities and subsequently avoid lock-in of high carbon emission patterns for travel. The results underscore a significant potential urbanization wedge for reducing energy use in rapidly urbanizing Asia, Africa, and the Middle East.
Street aspect ratios and urban thermal storage largely determine the thermal environment in cities. By performing scaled outdoor measurements in summer of 2017 in Guangzhou, China, we investigate ...these impacts on spatial/temporal characteristics of urban thermal environment which are still unclear so far. Two types of street canyon models are investigated, i.e. the ‘hollow’ model resembling hollow concrete buildings and the ‘sand’ model consisting of buildings filled with sand attaining much greater thermal storage. For each model, three street aspect ratios (building height/street width, H/W = 1, 2, 3; H = 1.2 m) are considered.
The diurnal variations of air-wall surface temperatures are observed and their characteristics are quantified for various cases. The daily average temperature and daily temperature range (DTR) of wall temperature vary significantly with different aspect ratios and thermal storage. During the daytime, wider street canyon (H/W = 1) with less shading area experiences higher temperature than narrower ones (H/W = 2, 3) as more solar radiation received by wall surfaces. At night, wider street canyon cools down quicker due to stronger upward longwave radiation and night ventilation. For hollow models, H/W = 1 attains DTR of 12.1 °C, which is 1.2 and 2.1 °C larger than that of H/W = 2, 3. Moreover, the sand models experience smaller DTR and a less changing rate of wall temperature than hollow models because larger thermal storage absorbs more heat in the daytime and releases more at night. DTR of hollow models with H/W = 1, 2, 3 is 4.5, 4.6 and 3.8 °C greater than sand models respectively. For both hollow and sand models, wider streets experience a little higher daily average temperature (0.3–0.6 °C) than narrower ones. Our study provides direct evidence in how man-made urban structures influence urban climate and also suggests the possibility to control outdoor thermal environment by optimize urban morphology and thermal storage.
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•Scaled outdoor measurements of urban climate (SOMUCH) in 2D street canyon are tested.•Impact of aspect ratio (H/W = 1,2,3; H = 1.2 m)/thermal storage on T profiles is studied.•Wider street is warmer in daytime and cools down quicker at night than narrower one.•Sand models with more thermal mass get less daily temperature range (DTR) than hollow models.•Upper walls receive more radiation in daytime but cool down quicker than lower walls.
The scaling of urban climate action and its governance is rapidly becoming a central focus in the urban climate governance literature and policy debates. Building on the broader scaling literature ...and inspired by related initiatives in other fields, this article calls for the development of a systematic “science of scaling” for urban climate governance. Such a science of scaling may help to give a better understanding of how well-performing urban climate action and its governance can be multiplied, accelerated and broadened (ie horizontal and vertical scaling and scaling out, up and down), and it may help to uncover scaling trajectories towards systemic change in cities (ie deep scaling).
Urban heat islands (UHI) in a city tend to vary with changes in time and space. To effectively cope with the accelerating intensity of UHI due to global warming and the resulting damage, it is ...essential to accurately analyze and understand the spatial and temporal variations of UHI. This study conducted a systematic literature review (SLR) to better understand how existing studies have classified and analyzed UHI variations. Research trends and limitations related to UHI variation were reviewed focusing on 55 studies extracted through a five-stage protocol to identify critical studies. The selected studies were analyzed and synthesized in detail. The results showed that studies use different research ranges, data collection methods, analysis, and prediction models depending on the type of UHI variation. These results also indicate that studies have not used universal and specific protocols that apply to UHI variations. To address the limitations of these studies, it is necessary to develop more specific UHI research design methods and an analytical model that reflects the three-dimensional elements of the collected data. In addition, researchers should develop indexes to explain the spatial and temporal variations of UHIs. Further studies can help establish policies and planning codes to counter the spatiotemporal variability of UHIs.
•Review of spatial and temporal variations of UHIs using an SLR framework.•Lack of general protocols to set the research scope and determine data collection methods to efficiently study UHI variations.•Need to develop a model and indexes to explain the intensity and magnitude of UHI variations.
Researchers have made immense progress in understanding the urban-induced microclimate by numerical modelling. It has been around two decades since urban canopy models now commonly employed in ...mesoscale atmospheric models for operational and applied research purposes have emerged. To drive further advancement, it is timely to conduct a review of the state-of-the-art and lessons learnt from the relevant literature. In this paper, 102 urban climate real case modelling studies published in 2000–2019 are reviewed. Patterns and preferences in their study locations, periods, model choices, land cover databases, topics discussed, and scenarios investigated are holistically examined. There is an evident improvement in model complexity and urban surface data precision during the period reviewed. Most studies focus on the urban thermal climate and effects of urbanization. Based on the research gaps identified, more work is needed on the currently underrepresented but vulnerable cities in developing countries with tropical, arid, and cold climates. Collaborative field campaigns, initiatives to characterize cities in a consistent manner, and multi-scale modelling approaches have proven to benefit the progress in urban climate studies and should therefore be encouraged. More importantly, efforts should be invested in translating the science into information relevant to human well-being, urban planning, and policymaking.
•102 urban climate modelling real case studies published in the 21st century are reviewed•Urban parameterization and surface description in atmospheric models have advanced•Urban heat island and the effect of urbanization are the most popular topics•More research is required for developing countries and multi-scale modelling systems•Urban climate research should be applied to urban planning and policymaking
Abstract This work presents a high‐resolution spatiotemporal analysis of the urban heat island (UHI) effect in Swiss cities during the last 6 years. The entire alpine country is simulated at once ...using the COSMO model at 1.1 km resolution, validated against a dense national measurement network. Additionally, the bulk parametrisation TERRA URB is used to model the dynamical and thermal effects of urban areas. The resulting data allows us to perform the first comprehensive analysis over the entire Switzerland, with a focus on the UHI effect with intra‐urban and across cities comparisons, and to report on the current state of urban warming. Despite the medium‐small size of the cities, the UHI is of considerable magnitude especially when considering peak values in ideal weather conditions. The present results confirm previous analyses performed for individual cities, and shed new light on the country‐wide picture by highlighting features such as the marked seasonality of the UHI intensity as well as the influence of local climate and topographical features on the urban climate. A thorough discussion is also presented highlighting the absence of simple relationships between UHI intensity and bulk city parameters and weather patterns.
O aumento da temperatura da superfície tem causado preocupação mundial, principalmente porque as modificações do ambiente urbano interferem consideravelmente no conforto ambiental. O desenvolvimento ...das cidades está frequentemente marcado pela remoção de cobertura vegetal, movimentação de terra e impermeabilização do solo. Para investigar um processo de urbanização acentuado e seus efeitos no microclima, estudou-se o município de Rio Verde, estado de Goiás, Brasil, no período de 1985 a 2019. Objetivou-se com este estudo, avaliar espaço-temporalmente as mudanças do uso e ocupação solo e seus impactos na temperatura da superfície no Município. Para isso, desenvolveu-se uma condição embasada num algoritmo de decisão hierárquica, para classificar especificamente a distribuição espacial de solos de Cerrado urbano. Foi utilizado dados extraídos de imagens orbitais dos satélites Landsat-5 e Landsat-8 no período de 1985 a 2019. Dentre os resultados, detectou-se o aumento de camadas de superfície termicamente ativas, resultando em alterações na temperatura da superfície demonstrando que a intensidade das ilhas de calor é superior em áreas de solos impermeabilizados. Este estudo por fim concluiu-se, que a expansão urbana, assim como os demais parâmetros ambientais ocasionados por esta, foram a principal força motriz e causa dessas modificações e impactos no microclima observados no município. Nesse sentido, as mudanças do uso e ocupação do solo resultou em alterações no comportamento térmico superficial ocasionado principalmente pela transformação do uso do solo.
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