The severity of urban heat islands (UHIs) is increasing due to global and urban climate change. The damage caused by UHIs is also increasing. To establish a plan to improve the deteriorating thermal ...environment in cities due to UHIs and to minimize the damage, further research is needed to accurately estimate and analyze the intensity and magnitude of UHIs. This systematic literature review (SLR) is an in-depth review of 51 studies obtained through a five-step filtering process focusing on their analysis of the spatial extent of UHIs, the UHI concept that was used for UHI estimation, and the UHI estimation and analysis methods. This SLR confirmed the need for accurate UHI intensity and magnitude estimation and analysis to reset the existing UHI classification based on the variety of vertical and horizontal ranges where UHIs occur. The results also indicated that the existing UHI energy concepts for estimating UHIs need to be modified and developed to reflect the three-dimensional physical form of the city. Finally, this SLR clarifies the need to develop an optimized analysis method for UHI research. The review results of this SLR will inform future studies and be the cornerstone for establishing policies and plans that can accurately predict and respond to the damage caused by UHIs.
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•Review intensity, magnitude estimation, and analysis of UHIs using an SLR framework.•Lack of general protocols to establish UHI classification criteria to efficiently estimate and analyze UHIs.•Need to develop a UHI estimation and analysis model considering a 3-D form of a city.•Need for further research to develop a model focusing on the intensity and magnitude of UHIs
Given the large transformation and fast-growing population that the Greater Toronto Area (GTA) is facing, and the increasing impact of climate change in urbanized areas, it is crucial to investigate ...strategies that could mitigate the effects of heat waves. In this paper, the effects of greenery enhancements are investigated using mesoscale and microscale simulations performed by the Weather Research and Forecasting model and the ENVI-met model, respectively. In particular, two vulnerable areas located in the GTA are investigated. Comparing the results of simulations with measurements show the differences in how mesoscale and microscale models predict the meteorological processes happening within the urban canopy and the local climate. Then, two mitigation scenarios, a moderate green scenario (MGS) and an intensive green scenario (IGS) are assessed considering different increases in the vegetation area. The results of the mesoscale simulations show that by increasing the greenery canopy, the maximum daily air temperature decreases by 1.6 to 2.3 °C, while the relative humidity increases by 10% to 12%. The microscale simulations show that increasing the tree canopy would cool the air temperature by 0.5 °C to 1.4 °C locally. Overall, depending on wind conditions and the arrangement of buildings and existing green areas, the cooling effect is shown to have an impact on up to 250 m downwind from the new green area locations. Finally, this study demonstrates that both mesoscale (WRF) and microscale (ENVI-met) modeling confirm similar results in how greenery enhancements may improve the human thermal comfort in the continental climate of the GTA.
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•The Weather Research and Forecasting (WRF) model is coupled with the urban canopy model•Meso- and microscale models are used to predict meteorological processes in the urban atmosphere and local climate•The outdoor thermal comfort effects of greenery infrastructure in the Great Toronto Area are assessed.•Mesoscale modeling shows that more greenery canopy could reduce the maximum temperature by 1.6 °C to 2.3 °C.•Microscale simulations show that increasing the tree canopy cools the local climate by 0.5 °C to 1.4 °C locally.
Urban Climates and Climate Change Masson, Valéry; Lemonsu, Aude; Hidalgo, Julia ...
Annual review of environment and resources,
10/2020, Volume:
45, Issue:
1
Journal Article
Peer reviewed
Open access
Cities are particularly vulnerable to extreme weather episodes, which are expected to increase with climate change. Cities also influence their own local climate, for example, through the relative ...warming known as the urban heat island (UHI) effect. This review discusses urban climate features (even in complex terrain) and processes. We then present state-of-the-art methodologies on the generalization of a common urban neighborhood classification for UHI studies, as well as recent developments in observation systems and crowdsourcing approaches. We discuss new modeling paradigms pertinent to climate impact studies, with a focus on building energetics and urban vegetation. In combination with regional climate modeling, new methods benefit the variety of climate scenarios and models to provide pertinent information at urban scale. Finally, this article presents how recent research in urban climatology contributes to the global agenda on cities and climate change.
The present study examines the temporal and spatial variability of near‐surface air temperature and the canopy layer urban heat island (UHI) in Singapore. Observations collected at 20 locations ...across the island city‐state and during 6 years make this one of the most extensive studies carried out in a tropical city. Local climate zones (LCZs), defined as urban built and rural land cover types which produce a unique air temperature response, are used to standardize intersite comparison. The results show that the choice of the rural reference can affect the night‐time UHI magnitude by up to 2°C under “ideal” (dry, clear, calm) conditions. The most frequently observed median UHI magnitude increases from 2.8 during all‐weather to 3.7°C during “ideal” conditions, respectively. A seasonality is present with lowest (highest) mean all‐weather values of ~2.0°C (~3.3°C), observed during the wet (dry) December–January (April–October) period. Mean night‐time UHI intensity across seven built‐type LCZs ranges between 1.8 and 3.5°C (2.5 and 4.3°C) for all‐weather (“ideal”) conditions. Corresponding daily values are 1.1–2.3°C (1.5–2.7°C). The lowest (highest) night‐time magnitudes are associated with open low‐rise LCZ 6 (compact high‐rise LCZ 1) built type. In the middle of the day LCZ 1 can experience a cool island effect. The average UHI values presented here give an indication of the extra warmth experienced in the built‐up spaces of Singapore relative to one possible rural reference land cover type (scattered trees LCZ B). Highest daytime heat exposure is observed in LCZs 3 and 8 which are characterized by low building heights, high impervious surface fraction and lack of vegetation. The present results can be used to support the development and evaluation of urban climate models, develop urban planning policies and improve local weather forecasts and the delivery of integrated urban services.
In situ observations reveal significant near‐surface air temperature variability across tropical Singapore. Differences between built‐type neighbourhoods and a reference “rural” background site vary according to local climate zone (LCZ), weather and season. Overall highest daytime temperatures are observed in neighbourhoods characterized by low‐rise buildings, high percentage of impervious surfaces and a lack of vegetation, where heat exposure is most severe.
The combination of global warming and urban sprawl is the origin of the most hazardous climate change effect detected at urban level: Urban Heat Island, representing the urban overheating respect to ...the countryside surrounding the city. This book includes 18 papers representing the state of the art of detection, assessment mitigation and adaption to urban overheating. Advanced methods, strategies and technologies are here analyzed including relevant issues as: the role of urban materials and fabrics on urban climate and their potential mitigation, the impact of greenery and vegetation to reduce urban temperatures and improve the thermal comfort, the role the urban geometry in the air temperature rise, the use of satellite and ground data to assess and quantify the urban overheating and develop mitigation solutions, calculation methods and application to predict and assess mitigation scenarios. The outcomes of the book are thus relevant for a wide multidisciplinary audience, including: environmental scientists and engineers, architect and urban planners, policy makers and students.
The Urban Climate and Resiliency-Science Working Group (i.e., The WG) was convened in the summer of 2018 to explore the scientific grand challenges related to climate resiliency of cities. The WG ...leveraged the presentations at the 10th International Conference on Urban Climate (ICUC10) held in New York City (NYC) on 6–10 August 2018 as input forum. ICUC10 was a collaboration between the International Association of Urban Climate, American Meteorological Society, and World Meteorological Organization. It attracted more than 600 participants from more than 50 countries, resulting in close to 700 oral and poster presentations under the common theme of “Sustainable & Resilient Urban Environments”. ICUC10 covered topics related to urban climate and weather processes with far-reaching implications to weather forecasting, climate change adaptation, air quality, health, energy, urban planning, and governance. This article provides a synthesis of the analysis of the current state of the art and of the recommendations of the WG for future research along each of the four Grand Challenges in the context of urban climate and weather resiliency; Modeling, Observations, Cyber-Informatics, and Knowledge Transfer & Applications.
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
Cities are generally warmer than their adjacent rural land, a phenomenon known as the urban heat island (UHI). Often accompanying the UHI effect is another phenomenon called the urban dry island ...(UDI), whereby the humidity of urban land is lower than that of the surrounding rural land
. The UHI exacerbates heat stress on urban residents
, whereas the UDI may instead provide relief because the human body can cope with hot conditions better at lower humidity through perspiration
. The relative balance between the UHI and the UDI-as measured by changes in the wet-bulb temperature (T
)-is a key yet largely unknown determinant of human heat stress in urban climates. Here we show that T
is reduced in cities in dry and moderately wet climates, where the UDI more than offsets the UHI, but increased in wet climates (summer precipitation of more than 570 millimetres). Our results arise from analysis of urban and rural weather station data across the world and calculations with an urban climate model. In wet climates, the urban daytime T
is 0.17 ± 0.14 degrees Celsius (mean ± 1 standard deviation) higher than rural T
in the summer, primarily because of a weaker dynamic mixing in urban air. This T
increment is small, but because of the high background T
in wet climates, it is enough to cause two to six extra dangerous heat-stress days per summer for urban residents under current climate conditions. The risk of extreme humid heat is projected to increase in the future, and these urban effects may further amplify the risk.
Understanding how cities develop climate plans is crucial to capture their potential to achieve ambitious climate goals. Previous literature has highlighted the role of external pressures or heroic ...actors in driving local changes. By highlighting the everyday practices of actors in urban climate planning, we reveal new sets of contradictions in climate governance. Drawing from social practice theory, this paper examines how contradictions were managed in the process of developing a new climate plan in Bergen, Norway. Through a variety of empirical sources, we explore the strategic value these offer, and the organisational work accomplished by the navigation of contradictions. We highlight three strategic benefits of negotiating contradictions: the legitimisation, expansion and signalling of climate work. In conclusion, the paper argues that considering practices of climate planning reveals novel forms of agency, namely the potential of mundane organisational processes and the pivotal role of civil servants in this work.
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