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, Letnik:
45, Številka:
1
Journal Article
Recenzirano
Odprti dostop
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 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 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 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.
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.
Improved representation of urban processes in Earth System Models (ESMs) is a pressing need for climate modeling and climate‐driven urban energy studies. Despite recent improvements to its fully ...coupled Building Energy Model (BEM), the current Community Land Model Urban (CLMU) in the Community Earth System Model (CESM) lacks the infrastructure to model air‐conditioning (AC) adoption explicitly. This undermines CESM's fidelity in modeling urban climate and energy use, and limits its use in climate and energy risk assessments. Here, we establish a new parameterization scheme in CESM that represents AC adoption explicitly through an AC adoption rate parameter in the BEM of CLMU, and build a present‐day, global, survey‐based, and spatially explicit AC adoption rate data set at country and sub‐country level that is integrated within CESM. The new data set can be leveraged for other ESMs or global‐scale models and analyses. The explicit AC adoption scheme and the AC adoption rate data set significantly improve the accuracy of anthropogenic heat modeling due to AC in CESM. The new parameterization scheme makes it possible to evaluate the effects of changing AC adoption on global urban energy and climate using CESM. These developments enhance CESM in its use for climate impact assessments under future climate and socioeconomic development scenarios, and represent continued efforts in better representing urban processes and coupled human‐urban‐Earth dynamics in ESMs.
Plain Language Summary
Human activities in cities, such as building energy use, need to be better represented in models designed to simulate urban climate around the world. The Community Land Model Urban is one such model that has been continuously improved, but still cannot effectively model varying air conditioning (AC) adoption rate across countries or regions. This limitation hinders the model's ability in simulating urban climate and building energy use. Here, we improve the model by developing a new explicit‐AC‐adoption parameterization that represents the proportions of buildings with AC systems, and constructing a global AC adoption rate data set at present‐day for all countries and regions in the world. These improvements help the model simulate the air‐conditioning energy use more accurately, and provide opportunities to evaluate the combined effects of climate change, population growth, and economic development on building energy use and climates for cities around the world.
Key Points
An explicit air‐conditioning adoption scheme is developed for the building energy model in the Community Land Model Urban
A global air‐conditioning adoption rate data set is built for Community Earth System Model, with potential for use in other global‐scale models and analyses
The new scheme and data set greatly improve model performance and enable more comprehensive climate and energy risk assessments
Increasing urbanization is likely to intensify the urban heat island effect, decrease outdoor thermal comfort, and enhance runoff generation in cities. Urban green spaces are often proposed as a ...mitigation strategy to counteract these adverse effects, and many recent developments of urban climate models focus on the inclusion of green and blue infrastructure to inform urban planning. However, many models still lack the ability to account for different plant types and oversimplify the interactions between the built environment, vegetation, and hydrology.
In this study, we present an urban ecohydrological model, Urban Tethys-Chloris (UT&C), that combines principles of ecosystem modelling with an urban canopy scheme accounting for the biophysical and ecophysiological characteristics of roof vegetation, ground vegetation, and urban trees. UT&C is a fully coupled energy and water balance model that calculates 2 m air temperature, 2 m humidity, and surface temperatures based on the infinite urban canyon approach. It further calculates the urban hydrological fluxes in the absence of snow, including transpiration as a function of plant photosynthesis. Hence, UT&C accounts for the effects of different plant types on the urban climate and hydrology, as well as the effects of the urban environment on plant well-being and performance.
UT&C performs well when compared against energy flux measurements of eddy-covariance towers located in three cities in different climates (Singapore, Melbourne, and Phoenix).
A sensitivity analysis, performed as a proof of concept for the city of Singapore, shows a mean decrease in 2 m air temperature of 1.1 ∘C for fully grass-covered ground, 0.2 ∘C for high values of leaf area index (LAI), and 0.3 ∘C for high values of Vc,max (an expression of photosynthetic capacity). These reductions in temperature were combined with a simultaneous increase in relative humidity by 6.5 %, 2.1 %, and 1.6 %, for fully grass-covered ground, high values of LAI, and high values of Vc,max, respectively. Furthermore, the increase of pervious vegetated ground is able to significantly reduce surface runoff.
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