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6 pages, 363 KiB

Open AccessEditorial

Introducing Urban Overheating—Progress on Mitigation Science and Engineering Applications

by Michele Zinzi and Matheos Santamouris

Climate 2019, 7(1), 15; https://doi.org/10.3390/cli7010015 - 19 Jan 2019

Cited by 7 | Viewed by 3995

Abstract

Buildings and construction is the most important economic sector in the world after agriculture [...] Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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Research

Jump to: Editorial

16 pages, 3448 KiB

Open AccessFeature PaperArticle

Leftover Spaces for the Mitigation of Urban Overheating in Municipal Beirut

by Noushig Kaloustian, David Aouad, Gabriele Battista and Michele Zinzi

Climate 2018, 6(3), 68; https://doi.org/10.3390/cli6030068 - 21 Aug 2018

Cited by 20 | Viewed by 6327

Abstract

The Urban Heat Island phenomenon and urban overheating are serious consequences of urbanization resulting in impacts on thermal comfort levels, heat stress and even mortality. This paper builds on previous findings on the topic of non-constructible parcels, small vacant or built spaces in [...] Read more.

The Urban Heat Island phenomenon and urban overheating are serious consequences of urbanization resulting in impacts on thermal comfort levels, heat stress and even mortality. This paper builds on previous findings on the topic of non-constructible parcels, small vacant or built spaces in Municipal Beirut, some of which belong to the municipality while others are privately owned and which might be used for different functional purposes. This paper further examines the possibility of implementing cool surface or paving materials and urban vegetation to reduce air urban temperature, especially during the summer period and with the view to project the positive findings of this case study to the entire Municipal Beirut area. A numerical analysis using ENVI-met 4.0 investigates the thermal performance of these non-constructibles further to implementation of high reflective surfaces and urban vegetation on a broad neighborhood scale, taking the Bachoura District as a reference case for a typical summer day. The best air temperature reductions correspond to the use of cool material in areas that are far from buildings where there are no shadow effects. In some cases, the introduction of trees leads to an increase of the air temperature near the ground because they became an obstacle of the natural ventilation. Results show a maximum mitigation effect with the use of cool materials that lead to reductions in air temperatures up to 0.42 °C if used alone and up to 0.77 °C if used in combination with trees. Within the framework of an integrated approach to planning, this form of urban intervention aims for substantial overheating reduction. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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24 pages, 8061 KiB

Open AccessArticle

Sky View Factor Calculation in Urban Context: Computational Performance and Accuracy Analysis of Two Open and Free GIS Tools

by Jérémy Bernard, Erwan Bocher, Gwendall Petit and Sylvain Palominos

Climate 2018, 6(3), 60; https://doi.org/10.3390/cli6030060 - 4 Jul 2018

Cited by 62 | Viewed by 14348

Abstract

The sky view factor (SVF) has an important role in the analysis of the urban micro-climate. A new vector-based SVF calculation tool was implemented in a free and open source Geographic Information System named OrbisGIS. Its accuracy and computational performance are compared to [...] Read more.

The sky view factor (SVF) has an important role in the analysis of the urban micro-climate. A new vector-based SVF calculation tool was implemented in a free and open source Geographic Information System named OrbisGIS. Its accuracy and computational performance are compared to the ones of an existing raster based algorithm used in SAGA-GIS. The study is performed on 72 urban blocks selected within the Paris commune territory. This sample has been chosen to represent the heterogeneity of nine of the ten Local Climate Zone built types. The effect of the algorithms’ input parameters (ray length, number of directions and grid resolution) is investigated. The combination minimizing the computation time and the SVF error is identified for SAGA-GIS and OrbisGIS algorithms. In both cases, the standard deviation of the block mean SVF estimate is about 0.03. A simple linear relationship having a high determination coefficient is also established between block mean SVF and the facade density fraction, confirming the results of previous research. This formula and the optimized combinations for the OrbisGIS and the SAGA-GIS algorithms are finally used to calculate the SVF of every urban block of the Paris commune. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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26 pages, 5109 KiB

Open AccessArticle

The Effect of Building Facades on Outdoor Microclimate—Reflectance Recovery from Terrestrial Multispectral Images Using a Robust Empirical Line Method

by Jonathan Fox, Paul Osmond and Alan Peters

Climate 2018, 6(3), 56; https://doi.org/10.3390/cli6030056 - 25 Jun 2018

Cited by 15 | Viewed by 6870

Abstract

Climate change and the urban heat island effect pose significant health, energy and economic risks. Urban heat mitigation research promotes the use of reflective surfaces to counteract the negative effects of extreme heat. Surface reflectance is a key parameter for understanding, modeling and [...] Read more.

Climate change and the urban heat island effect pose significant health, energy and economic risks. Urban heat mitigation research promotes the use of reflective surfaces to counteract the negative effects of extreme heat. Surface reflectance is a key parameter for understanding, modeling and modifying the urban surface energy balance to cool cities and improve outdoor thermal comfort. The majority of urban surface studies address the impacts of horizontal surface properties at the material and precinct scales. However, there is a gap in research focusing on individual building facades. This paper analyses the results of a novel application of the empirical line method to calibrate a terrestrial low-cost multispectral sensor to recover spectral reflectance from urban vertical surfaces. The high correlation between measured and predicted mean reflectance values per waveband (0.940 (Red) < r_s > 0.967 (NIR)) confirmed a near-perfect positive agreement between pairs of samples of ranked scores. The measured and predicted distributions exhibited no statistically significant difference at the 95% confidence level. Accuracy measures indicate absolute errors within previously reported limits and support the utility of a single-target spectral reflectance recovery method for urban heat mitigation studies focusing on individual building facades. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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25 pages, 10272 KiB

Open AccessArticle

Evaluation and Modeling of Urban Heat Island Intensity in Basel, Switzerland

by Andreas Wicki, Eberhard Parlow and Christian Feigenwinter

Climate 2018, 6(3), 55; https://doi.org/10.3390/cli6030055 - 21 Jun 2018

Cited by 38 | Viewed by 7389

Abstract

An increasing number of people living in urban environments and the expected increase in long lasting heat waves makes the study of temperature distribution one of the major tasks in urban climatology, especially considering human health and heat stress. This excess heat is [...] Read more.

An increasing number of people living in urban environments and the expected increase in long lasting heat waves makes the study of temperature distribution one of the major tasks in urban climatology, especially considering human health and heat stress. This excess heat is often underestimated because stations from national meteorological services are limited in numbers and are not representing the entire urban area with typically higher nocturnal temperatures, especially in densely built-up environments. For a majority of the population, heat stress is consequently monitored insufficiently. In this study, the factors influencing the nocturnal urban heat island have been evaluated in detail and have been tested using different spatial resolutions. A multiple linear regression model has been developed with predictors resulting from different data sources to model the urban air temperature distribution continuously. Results show that various datasets can be used for the prediction of the heat island distribution with comparable results, ideally run on a 200 m grid. Validation using random sampling indicated a RMSE clearly below the standard deviation of the measurements with an average around ~0.15 °C. The regression coefficients are varying within the nocturnal runs with best results around 22:00 CET (R² > 0.9). Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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25 pages, 21043 KiB

Open AccessArticle

Air-Temperature Response to Neighborhood-Scale Variations in Albedo and Canopy Cover in the Real World: Fine-Resolution Meteorological Modeling and Mobile Temperature Observations in the Los Angeles Climate Archipelago

by Haider Taha, Ronnen Levinson, Arash Mohegh, Haley Gilbert, George Ban-Weiss and Sharon Chen

Climate 2018, 6(2), 53; https://doi.org/10.3390/cli6020053 - 17 Jun 2018

Cited by 22 | Viewed by 6346

Abstract

To identify and characterize localized urban heat- and cool-island signals embedded within the temperature field of a large urban-climate archipelago, fine-resolution simulations with a modified urbanized version of the WRF meteorological model were carried out as basis for siting fixed weather monitors and [...] Read more.

To identify and characterize localized urban heat- and cool-island signals embedded within the temperature field of a large urban-climate archipelago, fine-resolution simulations with a modified urbanized version of the WRF meteorological model were carried out as basis for siting fixed weather monitors and designing mobile-observation transects. The goal was to characterize variations in urban heat during summer in Los Angeles, California. Air temperatures measured with a shielded sensor mounted atop an automobile in the summers of 2016 and 2017 were compared to model output and also correlated to surface physical properties focusing on neighborhood-scale albedo and vegetation canopy cover. The study modeled and measured the temperature response to variations in surface properties that already exist in the real world, i.e., realistic variations in albedo and canopy cover that are attainable through current building and urban design practices. The simulated along-transect temperature from a modified urbanized WRF model was compared to the along-transect observed temperature from 15 mobile traverses in one area near downtown Los Angeles and another in an inland basin (San Fernando Valley). The observed transect temperature was also correlated to surface physical properties characterizations that were developed for input to the model. Both comparisons were favorable, suggesting that (1) the model can reliably be used in siting fixed weather stations and designing mobile-transect routes to characterize urban heat and (2) that except for a few cases with opposite co-varying influences, the correlations between observed temperature and albedo and between observed temperature and canopy cover were each negative, ranging from −1.0 to −9.0 °C per 0.1 increase in albedo and from −0.1 to −2.2 °C per 0.1 increase in canopy cover. Observational data from the analysis domains pointed to a wind speed threshold of 3 m/s. Below this threshold the variations in air temperature could be explained by land use and surface properties within a 500-m radius of each observation point. Above the threshold, air temperature was influenced by the properties of the surface within a 1-km upwind fetch. Of relevance to policy recommendations, the study demonstrates the significant real-world cooling effects of increasing urban albedo and vegetation canopy cover. Based on correlations between the observed temperature (from mobile transects) and surface physical properties in the study domains, the analysis shows that neighborhood-scale (500-m) cooling of up to 2.8 °C during the daytime can be achieved by increasing albedo. A neighborhood can also be cooled by up to 2.3 °C during the day and up to 3.3 °C at night by increasing canopy cover. The analysis also demonstrates the suitability of using fine-resolution meteorological models to design mobile-transect routes or site-fixed weather monitors in order to quantify urban heat and the efficacy of albedo and canopy cover countermeasures. The results also show that the model is capable of accurately predicting the geographical locations and the magnitudes of localized urban heat and cool islands. Thus the model results can also be used to devise urban-heat mitigation measures. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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12 pages, 3498 KiB

Open AccessFeature PaperArticle

Multifractal Analysis of High-Frequency Temperature Time Series in the Urban Environment

by Stavroula Karatasou and Mat Santamouris

Climate 2018, 6(2), 50; https://doi.org/10.3390/cli6020050 - 8 Jun 2018

Cited by 11 | Viewed by 4920

Abstract

Continuous monitoring systems have been regarded as a very useful tool to provide continuous high-frequency measurements of many parameters. Here, we analyze high-frequency time series of air temperature measurements, recorded every 10 min during 2003 in Athens (Greece) by an online monitoring system [...] Read more.

Continuous monitoring systems have been regarded as a very useful tool to provide continuous high-frequency measurements of many parameters. Here, we analyze high-frequency time series of air temperature measurements, recorded every 10 min during 2003 in Athens (Greece) by an online monitoring system for the urban environment. We propose a set of time series analysis techniques, where missing data are well respected and information concerning the system’s dynamics is preserved. A power spectral density analysis is performed over time scales spanning from 10 min to several days. A scale-invariant behavior of the form

E (f) \approx f^{- β}

is revealed for scales below 9 h. Over this scaling range, we have performed structure functions analysis, and shown that air temperature data exhibit turbulent-like intermittent properties with multi-fractal statistics. The multifractal exponents obtained possess some similarities with passive scalar turbulence results. Although we illustrate the proposed approach using air temperature data, the method can be used as an efficient tool to analyse other environmental parameters monitored in urban environment. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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25 pages, 5750 KiB

Open AccessArticle

A Multi-Criteria Approach to Achieve Constrained Cost-Optimal Energy Retrofits of Buildings by Mitigating Climate Change and Urban Overheating

by Fabrizio Ascione, Nicola Bianco, Gerardo Maria Mauro, Davide Ferdinando Napolitano and Giuseppe Peter Vanoli

Climate 2018, 6(2), 37; https://doi.org/10.3390/cli6020037 - 8 May 2018

Cited by 36 | Viewed by 5222

Abstract

About 40% of global energy consumption is due to buildings. For this reason, many countries have established strict limits with regard to building energy performance. In fact, the minimization of energy consumption and related polluting emissions is undertaken in the public perspective with [...] Read more.

About 40% of global energy consumption is due to buildings. For this reason, many countries have established strict limits with regard to building energy performance. In fact, the minimization of energy consumption and related polluting emissions is undertaken in the public perspective with the main aim of fighting climate change. On the other hand, it is crucial to achieve financial benefits and proper levels of thermal comfort, which are the principal aims of the private perspective. In this paper, a multi-objective multi-stage approach is proposed to optimize building energy design by addressing the aforementioned public and private aims. The first stage implements a genetic algorithm by coupling MATLAB^® and EnergyPlus pursuing the minimization of energy demands for space conditioning and of discomfort hours. In the second stage, a smart exhaustive sampling is conducted under MATLAB^® environment with the aim of finding constrained cost-optimal solutions that ensure a drastic reduction of global costs as well as of greenhouse gas (GHG) emissions. Furthermore, the impact of such solutions on heat emissions into the external environment is investigated because these emissions highly affect urban overheating, external human comfort and the livability of our cities. The main novelty of this approach is the possibility to properly conjugate the public perspective (minimization of GHG emissions) and the private one (minimization of global costs). The focus on the reduction of heat emissions, in addition to the assessment of energy demands and GHG emissions, is novel too for investigations concerning building energy efficiency. The approach is applied to optimize the retrofit of a reference building related to the Italian office stock of the 1970s. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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16 pages, 27360 KiB

Open AccessArticle

Lighting Implications of Urban Mitigation Strategies through Cool Pavements: Energy Savings and Visual Comfort

by Giuseppe Rossi, Paola Iacomussi and Michele Zinzi

Climate 2018, 6(2), 26; https://doi.org/10.3390/cli6020026 - 7 Apr 2018

Cited by 18 | Viewed by 5633

Abstract

Cool materials with higher solar reflectance compared with conventional materials of the same color are widely used to maintain cooler urban fabrics when exposed to solar irradiation and to mitigate the Urban Heat Island (UHI). Photo-catalytic coatings are also useful to reduce air [...] Read more.

Cool materials with higher solar reflectance compared with conventional materials of the same color are widely used to maintain cooler urban fabrics when exposed to solar irradiation and to mitigate the Urban Heat Island (UHI). Photo-catalytic coatings are also useful to reduce air pollutants. Many studies related to these topics have been carried out during the past few years, although the lighting implication of reflective coatings have hardly been explored. To investigate these aspects, reflective coatings were applied on portions of a road and intensely analyzed in a laboratory and on the field. The applied cool coatings were found to have much higher solar and lighting reflectance than the existing road, which lead to lower surface temperatures up to 9 °C. Non-significant variations of chromaticity coordinates were measured under different lighting conditions. However, these materials showed a relevant variation of directional properties depending on the lighting and observation conditions with respect to conventional pavements. The optical behavior of these materials affects the uniformity of visions for drivers and requires ad-hoc installation of light sources. On the other hand, potential energy savings of up to 75% were calculated for the artificial lighting of a reference road. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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12 pages, 15355 KiB

Open AccessArticle

Subjective Human Perception of Open Urban Spaces in the Brazilian Subtropical Climate: A First Approach

by João Paulo Assis Gobo, Emerson Galvani and Cássio Arthur Wollmann

Climate 2018, 6(2), 24; https://doi.org/10.3390/cli6020024 - 3 Apr 2018

Cited by 15 | Viewed by 4766

Abstract

This research concerns a first approach to adapt the thermal comfort bands of the Physiological Equivalent Temperature (PET), New Standard Effective Temperature (SET), and Predicted Mean Vote (PMV) indices to Santa Maria’s population, Rio Grande do Sul, Brazil, on the basis of the [...] Read more.

This research concerns a first approach to adapt the thermal comfort bands of the Physiological Equivalent Temperature (PET), New Standard Effective Temperature (SET), and Predicted Mean Vote (PMV) indices to Santa Maria’s population, Rio Grande do Sul, Brazil, on the basis of the application of perception/sensation questionnaires to inhabitants while, at the same time, recording meteorological attribute data. Meteorological and thermal sensation data were collected from an automatic weather station installed on paved ground in the downtown area, which contained the following sensors: a scale gauge; a global radiation sensor; a temperature and humidity sensor; a speed and wind direction sensor; a gray globe thermometer. First of all, air temperature, gray globe temperature, relative air humidity, wind speed, wind gust, global solar radiation and precipitation were collected. People were interviewed using a questionnaire adapted from the model established by ISO 10551. The results demonstrated the efficiency of the linear regression model and the adequacy of the interpretive indexes, presenting results different from those analyzed by other authors in different climatic zones. These differences meet the analyzed literature and attest to the effectiveness of the calibration method of the PET, SET, and PMV indices for the Brazilian subtropical climate. After calibration, the PET index hit rate increased from 32.8% to 69.3%. The SET index, which had an initial hit rate of 34.6% before calibration, reached a hit-rate of 64.9%, while the PMV index increased from 35.9% to 58.7%. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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21 pages, 4034 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Increasing Surface Albedo on Urban Climate and Air Quality: A Detailed Study for Sacramento, Houston, and Chicago

by Zahra Jandaghian and Hashem Akbari

Climate 2018, 6(2), 19; https://doi.org/10.3390/cli6020019 - 21 Mar 2018

Cited by 51 | Viewed by 9203

Abstract

Increasing surface reflectivity in urban areas can decrease ambient temperature, resulting in reducing photochemical reaction rates, reducing cooling energy demands and thus improving air quality and human health. The weather research and forecasting model with chemistry (WRF-Chem) is coupled with the multi-layer of [...] Read more.

Increasing surface reflectivity in urban areas can decrease ambient temperature, resulting in reducing photochemical reaction rates, reducing cooling energy demands and thus improving air quality and human health. The weather research and forecasting model with chemistry (WRF-Chem) is coupled with the multi-layer of the urban canopy model (ML-UCM) to investigate the effects of surface modification on urban climate in a two-way nested approach over North America focusing on Sacramento, Houston, and Chicago during the 2011 heat wave period. This approach decreases the uncertainties associated with scale separation and grid resolution and equip us with an integrated simulation setup to capture the full impacts of meteorological and photochemical reactions. WRF-ChemV3.6.1 simulated the diurnal variation of air temperature reasonably well, overpredicted wind speed and dew point temperature, underpredicted relative humidity, overpredicted ozone and nitrogen dioxide concentrations, and underpredicted fine particular matters (PM_2.5). The performance of PM_2.5 is a combination of overprediction of particulate sulfate and underprediction of particulate nitrate and organic carbon. Increasing the surface albedo of roofs, walls, and pavements from 0.2 to 0.65, 0.60, and 0.45, respectively, resulted in a decrease in air temperature by 2.3 °C in urban areas and 0.7 °C in suburban areas; a slight increase in wind speed; an increase in relative humidity (3%) and dew point temperature (0.3 °C); a decrease of PM_2.5 and O₃ concentrations by 2.7 µg/m³ and 6.3 ppb in urban areas and 1.4 µg/m³ and 2.5 ppb in suburban areas, respectively; minimal changes in PM_2.5 subspecies; and a decrease of nitrogen dioxide (1 ppb) in urban areas. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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26 pages, 7774 KiB

Open AccessArticle

Assessment and Mitigation Strategies to Counteract Overheating in Urban Historical Areas in Rome

by Flavia Laureti, Letizia Martinelli and Alessandra Battisti

Climate 2018, 6(1), 18; https://doi.org/10.3390/cli6010018 - 18 Mar 2018

Cited by 22 | Viewed by 6007

Abstract

As urban overheating is increasing, there is a strong public interest towards mitigation strategies to enhance comfortable urban spaces, for their role in supporting urban metabolism and social life. The study presents an assessment of the existing thermal comfort and usage of San [...] Read more.

As urban overheating is increasing, there is a strong public interest towards mitigation strategies to enhance comfortable urban spaces, for their role in supporting urban metabolism and social life. The study presents an assessment of the existing thermal comfort and usage of San Silvestro Square in Rome during the summer, and performs the simulation of cooling strategies scenarios, to understand their mitigation potential for renovation projects. The first stage concerns a field analysis of the thermal and radiative environment on the 1st and 2nd of August 2014, including meteorological measurements and unobtrusive observations, to understand how people experience and respond to extreme microclimate conditions. In the second stage, the research proposes scenario simulations on the same day to examine the influence of cool colored materials, trees and vegetative surfaces on thermal comfort. The thermal comfort assessment was based on Physiologically Equivalent Temperature (PET), whereas microclimatic simulations were conducted with CFD calculations (ENVImet v.4.3.1). The first stage shows a strong relationship between lower PET values and attendance rate, depending on daily shading patterns. The second stage shows a relevant improvement of thermal comfort, with PET values of −12 °C comparing to the no-intervention scenario, associated with a combination of cool materials and trees. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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12 pages, 3689 KiB

Open AccessArticle

Recognition of Thermal Hot and Cold Spots in Urban Areas in Support of Mitigation Plans to Counteract Overheating: Application for Athens

by Thaleia Mavrakou, Anastasios Polydoros, Constantinos Cartalis and Mat Santamouris

Climate 2018, 6(1), 16; https://doi.org/10.3390/cli6010016 - 9 Mar 2018

Cited by 83 | Viewed by 6428

Abstract

Mitigation plans to counteract overheating in urban areas need to be based on a thorough knowledge of the state of the thermal environment, most importantly on the presence of areas which consistently demonstrate higher or lower urban land surface temperatures (hereinafter referred to [...] Read more.

Mitigation plans to counteract overheating in urban areas need to be based on a thorough knowledge of the state of the thermal environment, most importantly on the presence of areas which consistently demonstrate higher or lower urban land surface temperatures (hereinafter referred to as “hot spots” or “cold spots”, respectively). The main objective of this research study is to develop a methodological approach for the recognition of thermal “hot spots” and “cold spots” in urban areas during summer; this is accomplished with (a) the combined use of high and medium spatial resolution satellite data (Landsat 8 and Terra-MODIS, respectively); (b) the downscaling of the Terra-MODIS satellite data so as to acquire spatial resolution similar to the Landsat one and at the same time take advantage of the high revisit time as compared to the respective one of Landsat (16 days); and (c) the application of a statistical clustering technique to recognize “hot spots” and “cold spots”. The methodological approach was applied as a case study for the urban area of Athens, Greece for a summer period. Results demonstrated the capacity of the methodological approach to recognize “hot spots” and “cold spots”, revealed a strong relationship between land use and “hot spots” and “cold spots”, and showed that the average land surface temperature (LST) difference between the “hot spots” and “cold spots” can reach 9.1 °K. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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21 pages, 3040 KiB

Open AccessArticle

The Solar Reflectance Index as a Tool to Forecast the Heat Released to the Urban Environment: Potentiality and Assessment Issues

by Alberto Muscio

Climate 2018, 6(1), 12; https://doi.org/10.3390/cli6010012 - 15 Feb 2018

Cited by 44 | Viewed by 10911

Abstract

Overheating of buildings and urban areas is a more and more severe issue in view of global warming combined with increasing urbanization. The thermal behavior of urban surfaces in the hot seasons is the result of a complex balance of construction and environmental [...] Read more.

Overheating of buildings and urban areas is a more and more severe issue in view of global warming combined with increasing urbanization. The thermal behavior of urban surfaces in the hot seasons is the result of a complex balance of construction and environmental parameters such as insulation level, thermal mass, shielding, and solar reflective capability on one side, and ambient conditions on the other side. Regulations makers and the construction industry have favored the use of parameters that allow the forecasting of the interaction between different material properties without the need for complex analyses. Among these, the solar reflectance index (SRI) takes into account solar reflectance and thermal emittance to predict the thermal behavior of a surface subjected to solar radiation through a physically rigorous mathematical procedure that considers assigned air and sky temperatures, peak solar irradiance, and wind velocity. The correlation of SRI with the heat released to the urban environment is analyzed in this paper, as well as the sensitivity of its calculation procedure to variation of the input parameters, as possibly induced by the measurement methods used or by the material ageing. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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15 pages, 831 KiB

Open AccessArticle

How to Design a Park and Its Surrounding Urban Morphology to Optimize the Spreading of Cool Air?

by Jérémy Bernard, Auline Rodler, Benjamin Morille and Xueyao Zhang

Climate 2018, 6(1), 10; https://doi.org/10.3390/cli6010010 - 6 Feb 2018

Cited by 32 | Viewed by 6183

Abstract

Green areas induce smaller increases in the air temperature than built-up areas. They can offer a solution to mitigating the urban heat island impacts during heat waves, since the cool air generated by a park is diffused into its immediate surroundings through forced [...] Read more.

Green areas induce smaller increases in the air temperature than built-up areas. They can offer a solution to mitigating the urban heat island impacts during heat waves, since the cool air generated by a park is diffused into its immediate surroundings through forced or natural convection. The purpose of this study is to characterize the effect of several variables (park size, morphology of surrounding urban area, and wind speed) on the spreading of cool air. A parametric study is performed to run computational fluid dynamics simulations. The air temperature entering the computational domain was set at 35 °C, and the 2-m high surface included within the 34 °C isotherm was defined as an indicator of cool air spreading. The effects of park shape and orientation were negligible in comparison with size effects. The number of buildings was better correlated with the cooled surface area than the typical urban parameters identified in the literature (i.e., building density, aspect ratio, or mean building height). Since the number of buildings is obviously related to the number of streets, this result suggests that the greater the number of streets around a park, the wider the area that cool air spreads. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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13 pages, 9011 KiB

Open AccessArticle

Strategies for Development and Improvement of the Urban Fabric: A Vienna Case Study

by Milena Vuckovic, Aida Maleki and Ardeshir Mahdavi

Climate 2018, 6(1), 7; https://doi.org/10.3390/cli6010007 - 27 Jan 2018

Cited by 12 | Viewed by 6768

Abstract

Numerous studies have shown that densely developed and populated urban areas experience significant anthropogenic heat flux and elevated concentrations of air pollutants and CO₂, with consequences for human health, thermal comfort, and well-being. This may also affect the atmospheric composition and [...] Read more.

Numerous studies have shown that densely developed and populated urban areas experience significant anthropogenic heat flux and elevated concentrations of air pollutants and CO₂, with consequences for human health, thermal comfort, and well-being. This may also affect the atmospheric composition and circulation patterns within the urban boundary layer, with consequences for local, regional, and global climate. One of the resulting local implications is the increase in urban air temperature. In this context, the present contribution explores urban fabric development and mitigation strategies for two locations in the city of Vienna, Austria. Toward this end, the potential of specific planning and mitigation strategies regarding urban overheating was assessed using a state-of-the-art CFD-based (computational fluid dynamics) numeric simulation environment. The results display different levels of effectiveness for selected design and mitigation measures under a wide range of boundary conditions. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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3876 KiB

Open AccessFeature PaperArticle

Determination of the Surface and Canopy Urban Heat Island in Athens Central Zone Using Advanced Monitoring

by Chrissa Georgakis and Mattheos Santamouris

Climate 2017, 5(4), 97; https://doi.org/10.3390/cli5040097 - 20 Dec 2017

Cited by 25 | Viewed by 4847

Abstract

The present study aims to present all the findings of micro-climate measurements that were performed by the University of Athens in the center of Athens, during the summer period. The extended experimental campaign aimed to collect thermal and air flow measurements, in different [...] Read more.

The present study aims to present all the findings of micro-climate measurements that were performed by the University of Athens in the center of Athens, during the summer period. The extended experimental campaign aimed to collect thermal and air flow measurements, in different measuring points along a main street in the city center, in order to estimate the surface and canopy heat island intensity. In this work, the methodology of collecting the data, the experimental procedure, the equipment used, and lastly, the results are being presented. Comparison with the meteorological conditions that are recorded in the National Observatory of Athens, for the same period, lead to important conclusions about the local microclimate in the center of Athens and specifically the magnitude of the heat island effect. Particularly, in the denser area of the city after midday, air temperature increases reaching values up to 5 degrees higher than the one recorded in the suburban area. On the contrary, early in the morning the air temperature of the “green area” of the city was found to be lower up to 2 degrees than the corresponding in the suburban area. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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5041 KiB

Open AccessArticle

Influence of Urban Green Area on Air Temperature of Surrounding Built-Up Area

by Hideki Takebayashi

Climate 2017, 5(3), 60; https://doi.org/10.3390/cli5030060 - 7 Aug 2017

Cited by 21 | Viewed by 6380

Abstract

In this investigation, a numerical model expressing advection and diffusion effects is used to examine air temperature rise in urban areas that are on the leeward side of green areas. The model results are then verified by comparison with measurement results. When the [...] Read more.

In this investigation, a numerical model expressing advection and diffusion effects is used to examine air temperature rise in urban areas that are on the leeward side of green areas. The model results are then verified by comparison with measurement results. When the measurement point is at a distance of 30 m or more from a green area, the air temperature of the urban area is not affected by the green area. An isotropic diffusion model and a model incorporating buoyancy were applied for the vertical diffusion term. Results of air temperature rise with distance from the green area were compared for both calculated and measured values. The rise in air temperature due to the development of the urban boundary layer in the area near a green space is expressed using the sensible heat flux from the ground surface, the distance from the green area and the wind velocity. We considered an approximation of air temperature rise in order to express the following situation: when entering the urban area, air temperature rises sharply, and when reaching a certain distance from a green area, it becomes almost constant. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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Open AccessFeature PaperArticle

Characterization of Urban Heat and Exacerbation: Development of a Heat Island Index for California

by Haider Taha

Climate 2017, 5(3), 59; https://doi.org/10.3390/cli5030059 - 5 Aug 2017

Cited by 28 | Viewed by 10409

Abstract

To further evaluate the factors influencing public heat and air-quality health, a characterization of how urban areas affect the thermal environment, particularly in terms of the air temperature, is necessary. To assist public health agencies in ranking urban areas in terms of heat [...] Read more.

To further evaluate the factors influencing public heat and air-quality health, a characterization of how urban areas affect the thermal environment, particularly in terms of the air temperature, is necessary. To assist public health agencies in ranking urban areas in terms of heat stress and developing mitigation plans or allocating various resources, this study characterized urban heat in California and quantified an urban heat island index (UHII) at the census-tract level (~1 km²). Multi-scale atmospheric modeling was carried out and a practical UHII definition was developed. The UHII was diagnosed with different metrics and its spatial patterns were characterized for small, large, urban-climate archipelago, inland, and coastal areas. It was found that within each region, wide ranges of urban heat and UHII exist. At the lower end of the scale (in smaller urban areas), the UHII reaches up to 20 degree-hours per day (DH/day; °C.hr/day), whereas at the higher end (in larger areas), it reaches up to 125 DH/day or greater. The average largest temperature difference (urban heat island) within each region ranges from 0.5–1.0 °C in smaller areas to up to 5 °C or more at the higher end, such as in urban-climate archipelagos. Furthermore, urban heat is exacerbated during warmer weather and that, in turn, can worsen the health impacts of heat events presently and in the future, for which it is expected that both the frequency and duration of heat waves will increase. Full article

(This article belongs to the Special Issue Urban Overheating - Progress on Mitigation Science and Engineering Applications)

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