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  • 1.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    A városi tér szerkezete és hatása a mikroklímára [Urban space and structure and its effect on the urban microclimate]2017Ingår i: 43. Meteorológiai Tudományos Napok. 2017. November 23-24. Mikro- és mezoskálájú légköri folyamatok modellezése. Az előadások összefoglalói. / [ed] István Geresdi, Ferenc Ács, Balázs Szintai, and Tamás Weidinger, Budapest, Hungary, 2017Konferensbidrag (Refereegranskat)
    Abstract [hu]

    A városok sajátos éghajlata, a városklíma, a természetes környezethez képest módosult éghajlattal jellemezhető. A klímaparaméterek városi módosulásának hátterében a beépített felszínek megváltozott energiaháztartása áll. Míg a városok éghajlata markánsan elkülönül a környező természetes területek éghajlatától, a városokon belül is jelentős klimatikus különbségek alakulnak ki. Ezen különbségek kialakulására alapvető hatással van a beépítettség foka, valamint a zöld területek részaránya. A városokon belüli éghajlati különbségek tanulmányozása mérések és numerikus szimulációk révén lehetséges. Utóbbiak segítségével széleskörűen tanulmányozható a beépítettség, a városokra jellemző mesterséges anyagok, valamint a városon belül alkalmazott zöld- és kék infrastruktúra elemeinek hatása a kialakuló mikro- és lokális éghajlatra, illetve mindezek hatása a lakosok komfortérzetére. Eme ismeretanyagra alapozva megfogalmazhatók olyan várostervezési irányelvek, melyekkel az éghajlatváltozással kombinálódó városklíma negatív hatásai mérsékelhetőek, s a városlakók számára klimatikus szempontból élhetőbb környezet teremthető.Tanulmányomban Budapest jellemző városi beépítési formáit, s a köztük lévő mikroklimatikus különbségeket vizsgálom numerikus szimulációk útján, különös tekintettel a nyári hőterhelés mérséklésére irányuló várostervezési beavatkozások eredményességére az egyes beépítési formák esetén. Az egyik ilyen beavatkozás az épülethomlokzatok albedójának növelése nagyobb sugárzás-visszaverő képességű anyagok, illetve festékek alkalmazása révén. Egy másik jellemző beavatkozás a zöldterületek részarányának növelése, melyet tanulmányomban a lombkorona borítás értékének változtatásával vizsgálok. A különféle beépítési formák, homlokzat albedók és korona borítottság értékek komplex hatásának feltárására az ENVI-met szimulációs software-t alkalmaztam. Az eredmények alapján elmondható, hogy a megnövekedett albedó következtében a napsugárzásnak kitett homlokzatok hőmérséklete – s ez által az épületek hőterhelése is – csökken. A visszavert sugárzási hányad megnövekedése azonban az épületek között sugárzás többletként jelenik meg, mely többlet a nem módosított albedójú felületek (utak, terek) nagyobb sugárzási terheléséhez és ezáltal a városi határréteg felmelegedéséhez vezet. Ezzel ellentétben, a korona borítottság növelése a városi határrétegben a rövidhullámú sugárzás és a léghőmérséklet csökkenését eredményezi. Mivel ezen tényezők hatása a lakosok komfortérzetét és az épületeket érő hőterhelést is előnyösen befolyásolja, a közterületek fásítása a nyári hőterhelés mérséklésére irányuló várostervezési beavatkozás egyik hatásos eszköze lehet.

  • 2. Gál, Csilla V
    Experiencing Urban Climate in the Nation's Capital2015Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
  • 3.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Mean radiant temperature modeling, A comparative model evaluation2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    As a result of the changing climate with trends of rising temperatures and increasing extreme heat events, urban planners and city officials have recently taken a great interest in improving the climate of cities and maintaining comfortable outdoor conditions in spite of these trends.In order to meet the demand for this special knowledge and to deliver scientific assistance, several numerical models have emerged with an aim to assess the microclimate of cities and their influence on human thermal comfort over the course of the past decade. While these tools differ both in the human thermal comfort indices they deliver and in their numerical modeling approach, they all rely on the calculation of mean radiant temperature—the driving parameter of outdoor human thermal comfort. While the assessment of models lags behind the perpetual software updates and releases, the documentation of many such models is also lacking or insufficient. In addition, a great deal of existing validation studies assess clear cut situations where the site is either sunlit or in shade, whereas conditions in the urban environment are generally more complex. Given both the growing importance the outdoor thermal environment of cities and the role played by these tools, reporting on their performance is of high importance.The aim of this study is to assess the ability of several recently emerged or updated microclimate models to reproduce mean radiant temperature (Tmrt) in a complex urban setting. The evaluation is made against field data obtained by integral radiation measurements. Results indicate that most microclimate models underestimate Tmrt both at sunlit locations and at night, whereas in shade Tmrt is generally overestimated. These errors are related to the surface temperature parametrization, the isotropic sky assumption, simplifications in the reflected shortwave radiation calculation and the incorrect representation of a standing person.

  • 4. Gál, Csilla V
    Microclimate assessment of urban block typologies, a simulation approach2012Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Urban environments are characterized by a diversity of microclimates. To manage this complexity, assessments generally involve a certain kind of simplification: either an areal constriction (e.g. the analysis of distinct urban squares), or a spatial reduction (e.g. the reliance on the urban canyon model). This paper approaches the task at the scale of the urban block. In the analysis of metropolitan urban block typologies, the study adopts Probáld's concept of microclimate assemblages. With the presented approach, the research aims to compliment existing urban microclimate assessments. Utilizing the numerical modelENVI‐met, this paper focuses on the effect of building configurations.

  • 5.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Modeling mean radiant temperature in outdoor spaces: A comparative numerical simulation and validation study2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cities are increasingly under pressure to address the challenges of climate change. One of the most pressing and unifying issue in this respect is the maintenance of comfortable outdoor conditions despite rising air temperatures and increasing extreme heat events. As a means to inform urban planner and city officials, the assessment of outdoor thermal comfort conditions—either via numerical modeling or field measurements—have gained popularity over the past decade. While measurements can deliver highly accurate data, they are expensive and time-consuming endeavors that can only inform us about the conditions in an existing environment on a specific day and time of the year. In contrast, numerical modeling allows us to evaluate alternative urban design scenarios as well as to grasp the spatial and temporal variability of outdoor human thermal comfort conditions.

    Given the advantages of numerical modeling and the increasing computational power of personal computers, several tools have emerged with an aim to assess the microclimate and human thermal comfort impacts of urban planning and design decisions. While these tools differ both in the human thermal comfort indices they deliver and in their numerical modeling approach, they all rely on the calculation of mean radiant temperature, in one way or another. Mean radiant temperature (Tmrt), the driving parameter of human thermal comfort in outdoor spaces, requires the modeling of both short- and long waver radiation fluxes. While different calculation methods exist to deriving this parameter, most models also introduce some kind of numerical simplification to increase computational speed. The multitude of numerical approaches in deriving Tmrt, coupled with the high spatial and temporal variability of this parameter, can result in a range of values delivered by these tools. Given both the growing importance of improving the outdoor thermal environment of cities and the role these tools play in it, reporting on their performance is of high importance.

    The aim of this study is to assess popular microclimate models in their ability to reproduce the complex radiative environment of cities, as indicated by Tmrt, and to inform to the research and design community about their performance, compared to integral radiation measurement derived filed data. While the documentation of some numerical simulation tools is lacking or incomplete, this paper will nevertheless attempt to shed lights on the reasons behind the disparities in the derived Tmrt values. Initial results indicate that most microclimate models have a tendency to underestimate nighttime Tmrt together with daytime values when the location is exposed to the sun. In contrast, when the locations become shaded, Tmrt values are generally overestimated. In general, these errors indicate issues with surface temperature parametrization and point to the greatest challenge of the numerical simulation community.

  • 6. Gál, Csilla V
    Revisiting the urban block in the light of climate change: A case study of Budapest2014Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Since the beginning of the twentieth century, the urban block configuration of free-standing buildings has been deemed superior to other built forms, as it provided the necessities of modern healthy living: sunlight and fresh air. In light of climate change, the dissertation aims to reevaluate these long held beliefs and to reintroduce microclimate as an urban design consideration. The study takes four metropolitan block typologies of Budapest as cases to clarify the microclimate influence of key urban design parameters by means of a numerical simulation study. The effects of built form, orientation, vegetation and facade properties are evaluated for a typical summer day. The cases are assessed on the basis of diurnal potential air and mean radiant temperatures within the urban canopy layer. Numerical modeling is performed by ENVI-met and analysis is conducted with MATLAB. The findings indicate that built form and vegetation are key factors governing the microclimate. During the day, intraurban cool island develops between dense configurations and in tree-shaded urban canopies. Orientation is decisive in configurations with large open spaces, where east-west alignment corresponds with peak radiant and air temperatures. Apart from albedo, facade properties have little effect on the microclimate. The rise of air temperature with facade albedo is the outcome of canopy floor heating, resulting from the increased ratio of reflected shortwave radiation. A short-term field experiment was conducted in Budapest to complement the numerical simulation study and to evaluate ENVI-met. The measurement campaign utilized six air temperature and humidity loggers. Additionally, wind speed, air temperature and humidity were recorded at the pedestrian level during an anticyclonic period. In courtyards, thermal stratification developed by day with cool island intensities up to 7 C. In the case of open configurations, neither cool island, nor stratification was observed. The comparison of measured and predicted air temperatures revealed the strengths and weaknesses of the numerical model. In general, predicted temperatures had a decreased diurnal range with maximum values systematically underestimated. ENVI-met also failed to reproduce the thermal stratification in courtyards. Despite these shortcomings, the predicted trends and the relative microclimate differences between the configurations agreed with observations reasonably well.

  • 7.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    The effectiveness of shade trees for urban heat mitigation, a comparative numerical simulation study2016Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    As a result of climate change, many regions are projected to see increases in air temperatures and extreme heat events over the coming decades. Since these trends are expected to exacerbate existing conditions in cites, urban heat mitigation will be one of the key challenges of the twenty-first century. A frequently advocated means of mitigating urban heat is through shade trees. Through the reduction of air and radiative temperatures trees not only improve outdoor human thermal comfort, but also reduce the cooling loads of buildings. This paper investigates the impact of different canopy cover ratios and tree layouts on the urban microclimate. The numerical simulation study utilizes four characteristic dense urban configurations from Budapest (Hungary) to assess the influences of these factors on the effectiveness of shade trees in mitigating urban heat. The study applies ENVI-met for microclimate simulation and MATLAB for the analysis and visualization of the results. Microclimate conditions within the urban canopy layer are examined on the basis of diurnal air and mean radiant temperatures. Preliminary results indicate that the effectiveness of shade trees is the function of the urban configurations' initial thermal performance. Since microclimate improvements by way of trees are primarily achieved through shading, greatest reduction in radiative temperatures is achieved in configurations with large open spaces. In the case of air temperature, increasing the canopy cover increases the added benefit of temperature reduction—indicating that reduced turbulence can in certain cases be beneficial.

  • 8. Gál, Csilla V
    The impact of built form on the urban microclimate at the scale of city blocks2014Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Following the first oil crisis, Philip Steadman concluded that as a result of the twentieth-century developments in architecture "the means for environmental control within and around buildings, which was formerly achieved through effects of mutual shading, enclosure and wind protection, [were] lost" (Steadman 1975). Nevertheless, subsequent building regulations further strengthened the already prevailing design emphasis on single buildings by introducing energy measures that largely disregarded the effects of the surrounding environment [of the local climate]. While in countries with mild to moderate climates wintertime energy conservation became the primary preoccupation, climate model projections indicate rising temperatures and prolonged heat waves in these parts of the world. As a consequence, architects and planners increasingly find themselves ill equipped to address the challenges of climate change.The aim of this paper is to assess the microclimate performance of built form at the scale of city blocks. The study takes four metropolitan urban block typologies from Budapest as models. The purpose of this analysis is to obtain basic understanding regarding the interaction between built forms and microclimates in general, and to gain knowledge regarding the microclimatic behavior of these existing typologies in particular. The understanding of the performance of these forms is necessary both for developing climate- sensitive design principles and for proposing effective climate mitigation strategies.The comparative numerical simulation study utilizes ENVI-met and MATLAB. The models are compared on the basis of diurnal air temperature, mean radiant temperature and Predicted Mean Vote cycles. The analysis found mean radiant temperature a good indicator of the built form's influence on the canopy layer thermal environment. It is sensitive to directionalities in the model and signals problematic periods and places with high surface and air temperatures. Consequently, mean radian temperature that governs outdoor thermal comfort on warm and hot days is also useful to analyzing and understanding the effects of mutual shading.

  • 9. Gál, Csilla V
    The influence of built form and vegetation on the canopy layer microclimate within urban blocks2014Ingår i: Acta Climatologica et Chorologica, ISSN 1587-5903, Vol. 47-48, s. 43-52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A numerical simulation study was conducted to reveal the effects of built form on the canopy layer microclimate at the scale of city blocks and to evaluate the role of vegetation in modifying these environments. The study took four metropolitan urban block typologies from Budapest as models and compared their microclimate dynamics with and without vegetation. Microclimate modeling was performed by ENVI-met (Bruse 2011), while MATLAB was utilized for the data analysis. The findings indicate that built form and vegetation are key factors governing the canopy layer microclimate. Their influence is primarily exerted through shading and enclosure.

  • 10. Gál, Csilla V
    The influence of built form on the microclimate within urban blocks2014Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Urban morphology, that is the characteristic size, shape, orientation and distribution of buildings, plays a significant role in affecting the climate within cities. However, despite computational advances over the past decades, simulation studies investigating the effect of built form on the microclimate generally adopt either the array of cubes or the urban canyon model. What these models leave out are the microclimatic conditions within urban blocks and other complex environments that also constitute spaces of human activity. While the recently developed local climate zone (LCZ) classification system also took urban morphology to delineate ten urban categories, it also conceptualized built form as a cluster of free-standing buildings and therefore failed to account for semi-enclosed spaces. The aim of this study is to assess the effect of built form on the microclimate at the scale of the urban block. Taking the built environment of Budapest as a starting point, the study compares the microclimatic performance of four historic metropolitan urban block typologies. The comparative numerical study focuses on the influence of built form and orientation, and employes both a three- dimensional microclimate model (ENVI-met) and a high-level language for numerical computation and visualization (MATLAB). The presentation will compare the diurnal-cycles of air temperature, mean radiant temperature and Predicted Mean Vote of the four urban block configurations. The insights of this study could facilitate the development of targeted climate change adaptation strategies.

  • 11. Gál, Csilla V
    The influence of facade properties on the canopy layer microclimate within city blocks2014Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The application of high albedo surfaces and 'cool' materials — characterized by high solar reflectance and emissivity — are often advocated as a means to mitigate the urban heat island (UHI), to decrease indoor temperatures and consequently to reduce cooling loads in warm weather. The frequently described mechanism that links higher surface albedos with lower outdoor temperatures emphasizes the role of decreased surface temperatures in the process. Admittedly, the high albedo approach to UHI mitigation is primarily recommended for roofs, which, compared to roads and facades, have less obstructed sky views. During the day, the higher sky view factor of roofs prevents the trapping of radiation within the urban texture, and ensures a better radiative cooling by night. Nevertheless, the high albedo approach and the application of `cool materials' are increasingly recommended for both urban roads (Akbari, Pomerantz, and Taha 2001; Alchapar, Correa, and Cantón 2014; Santamouris et al. 2012; Santamouris, Synnefa, and Karlessi 2011; Synnefa et al. 2011; Zinzi, Carnielo, and Fasano 2012) and facades (Bougiatioti et al. 2009; Doya, Bozonnet, and Allard 2012; Synnefa, Santamouris, and Apostolakis 2007). The goal of this study is to investigate the role of facade surface properties on the canopy layer microclimate in a dense urban context.

  • 12. Gál, Csilla V
    The influence of shade trees on the canopy layer microclimate within urban blocks: a numerical simulation study2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Over the coming decades, many locatons are predicted to see warmer temperatures and more frequent extreme heat events as a result of climate change. Rising temperatures, coupled with the urban heat island effect, are expected to exacerbate existng conditons in cites. As a consequence, heat mitgaton in urban areas is antcipated be one of the key challenges of the twenty-first century. A frequently advocated means of mitgatng the urban heat island is through shade trees. Through the reducton of air and radiatve temperatures, they also improve the outdoor human thermal comfort and reduce building cooling loads. Utlizing four Hungarian metropolitan block typologies as cases, a numerical simulaton study is carried out to assess the impact of shade trees on the microclimate within urban blocks. The study applied ENVI-met for microclimate simulaton and MATLAB for the analysis and visualizaton of the results. Microclimate conditons within the blocks---with and without trees---are examined on the basis of diurnal air and mean radiant temperatures. Findings indicate that microclimate improvement by way of trees are primarily achieved through shading. The greatest reducton in daytme air and radiatve temperatures is achieved in configuratons with large open spaces, suggestng that effectve heat mitgaton strategies should also consider the interference between the shading of trees and buildings.

  • 13. Gál, Csilla V
    Urban design and building regulation changes in the transformation of the urban block: A design analysis though the lens of urban climatology in Budapest2011Ingår i: City Weathers: Meteorology and Urban Design 1950-2010 / [ed] Michael Hebbert, Vladimir Jankovic and Brian Webb, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hungary witnessed limited climatic considerations in the practice of architecture and urban planning in the past. The omission of urban climate related issues was — and still is — essentially the outcome of the prevailing technocratic approach. This negligence, coupled with the growth in motor vehicle ownership, changing building design and air-conditioning practices, contributed to the the deterioration of the urban atmospheric environment over the last decades. The efforts to improve dwelling conditions over previous centuries, culminated in several waves of urban design and planning reforms. The outcome of these changing forces was the evolution of the Budapest urban block. During the twentieth century, its development followed the line described by Ernst May (‘from the block to the slab'), only to surpass it with hybrid forms in the twenty-first. This paper, focusing on the transformation of the Budapest urban block, sets forth to provide a historic cross section from the period of the city’s late industrialization to present day. The analysis of this process is facilitated though the identification and use of urban block typologies: each representing distinct urban design and regulatory paradigms. By reviewing the main forces that influenced the emergence of different urban block typologies, and subsequently, presenting an analysis of the resultant configurations, the author aims at introducing climatic considerations into urban design. Downtown urban blocks are at the center of this study, as they represent the most crucial section of the city. These blocks are not only exposed to the highest intensities of the urban heat island effect, but are also facing drear consequences due to the lack of urban green spaces. Because the study aims at addressing urban living and urban environmental concerns, the analysis is focused on existing metropolitan housing models. The first part of the paper presents the evolution of aesthetic, hygienic, structural and other concerns that contributed to the development of Budapest urban block, as well as, identifies the four developed typologies. The second part of the paper presents an analysis by juxtaposing the main regulatory principles and the resultant typologies, in an attempt to pinpoint measures that both effects micro-climate, as well as, are within the control of urban planning, design or architecture. The aim of this analysis is to bring forth the readily available regulatory measures that could become climate- sensitive design guidelines in the future. The outcome of this paper aims to inform policy makers, urban planners, architects and other building professionals regarding the necessity of the inclusion of climate- sensitive design principles into our current design and regulatory practices. In order to extend our understating of this subject -- regarding the casual relationship between urban design parameters and the resultant microclimates --, the author argues for further microclimatic investigations. These subsequent studies will clarify and support the emerging climate-sensitive urban design guidelines, which in turn could ameliorate the existing microclimatic conditions.

  • 14. Gál, Csilla V
    Urban greening and cool surfaces: the effectiveness of climate change adaptation strategies within the context of Budapest2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Regional climate projections for Central and Eastern Europe indicate a rise in summertime temperatures along with an increase in the frequency of warm temperature extremes by the end of the next century. In the case of Hungary, models indicate a 1.7–2.6°C rise in summer temperatures in the near future, and a 3.5–6.0°C increase is projected for the end of the twenty-first century—based on the A1B scenario. Besides rising temperatures, long term projections also signal a 20–40% decrease in summer precipitation in Hungary. In Budapest, the existing urban heat island (UHI) intensity of 4–8°C is expected to make these already adverse projections worse. Since the combined influences of these phenomena will be most pronounced in the densely built and populated areas of the city, identifying effective UHI mitigation and climate change (CC) adaptation strategies for these ares is of primary importance. This paper investigates the impact of cool roofs and pavements along with the influence of different canopy cover ratios on the urban canopy layer (UCL) climate for a summer day, and assesses their impact on human thermal comfort under projected climate conditions at the pedestrian level. The goal is to evaluate the effectiveness of these popular CC adaptation actions and to contribute to the development of a systematic framework for the assessment of UHI mitigation strategies. The study took four dense urban configurations from Budapest—characteristic to most Central European cities—to examine the effectiveness of these approaches. The numerical simulation study utilizes ENVI-met and MATLAB. Preliminary results indicate that the performance of CC adaptation strategies is the function of the configurations' initial thermal performance. Consequently, the starting point of any adaptation proposals should be the evaluation of the initial thermal behavior of the selected focus area, followed by the selection of appropriate strategies—based on both the shortcomings of the initial local or microclimate, and the available opportunities for improvements. This study is a first attempt to quantify key CC adaptation strategies for Budapest. The results of this research will provide feedback to local authorities on the effectiveness of the assessed approaches and foster the articulation of more precise and economic CC adaptation actions and measures.

  • 15.
    Gál, Csilla V
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Gulyás, Ágnes
    Kántor, Noémi
    Heat mitigation with shade trees: the role of landscape design and tree parameters in ameliorating summertime heat stress in a Central-European square2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Climate change projections for Central Europe indicate a significant rise in summertime temperatures and an increase in the frequency and severity of extreme heat events. Combined with the peculiar climate of cities—characterized by the Urban Heat Island effect and reduced ventilation due to high building density—climate change is expected to have more pronounced effects in urban environments. Shade trees are demonstrated to be one of the most effective means to mitigate heat stress in cities. However, very few studies have evaluated systematically the impact of different landscape design and tree parameters (e.g. the species selection or the spatial distribution) on the heat mitigation effectiveness of shade trees. This study aims to assess the role of vegetation transmissivity, canopy size and tree distribution in a medium-sized Central-European square. The rectangular Bartók Square, located in the inner city of Szeged (Hungary), was selected as a study area. The numerical simulations were carried out with the radiation model SOLWEIG (v.2015a). The necessary meteorological data, collected on clear and warm summer day, was obtained from a nearby weather station run by the Hungarian Weather Service. The default model was built on the basis of available GIS data and utilized tree related parameters from detailed field measurements (tree location, canopy size and shape, etc.). Crown transmissivity data originated from a preliminary, long-term radiation measurement survey covering the vegetation period. Alternative scenarios were constructed with the following characteristics:1) keeping the original tree layout of the square, the initial tree crown transmissivity of 0.0678 was changed to small (0.0243) and high (0.1328) values;2) keeping the original canopy volume, two additional scenarios were introduced with evenly distributed trees of different crown sizes: that of several small trees and of fewer large ones;3) keeping the original canopy volume and using the same number and size of trees, we assessed the role of tree distribution by introducing a scenario were the trees were arranged along the bounding facades of the square—this scenario was compared to the evenly distributed configuration. In order to evaluate the impact of vegetation, all scenarios are reported in reference to a theoretical, nonvegetated square. Since several studies revealed that mean radiant temperature (Tmrt) plays a key role in summertime heat stress in the European context, this parameter was selected as performance indicator. Tmrt combines the heat effect of all short-and long-wave radiation fluxes reaching the human body. Our results indicate that when shade is provided for the facades only, the nighttime Tmrt surplus nearly disappears. However, while horizontal long-wave radiation fluxes have a greater impact on human thermal comfort due to the different absorption coefficients of the human body (0.7 vs. 0.95 for short and long-wave radiation, respectively), providing shade for the facades only is not a successful daytime heat mitigation strategy in open urban places. Comparing the influence of vegetation transmissivity revealed that low transmissivity species were able to reduce Tmrt by only 2C on average during the day. According to our case study, when transmissivity and canopy volume is kept constant, considerable mean radiant temperature reduction can be achieved by evenly distributed mature trees.

  • 16.
    Johansson, Sverker
    Högskolan för lärande och kommunikation, Högskolan i Jönköping, HLK, Ämnesforskning.
    The Faint Young Sun1999Rapport (Övrig (populärvetenskap, debatt, mm))
  • 17. Kovács, Attila
    et al.
    Unger, János
    Gál, Csilla V
    Kántor, Noémi
    Adjustment of the thermal component of two tourism climatological assessment tools using thermal perception and preference surveys from Hungary2016Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 125, nr 1-2, s. 113-130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study introduces new methodological concepts for integrating seasonal subjective thermal assessment patterns of people into the thermal components of two tourism climatological evaluation tools: the Tourism Climatic Index (TCI) and the Climate-Tourism/Transfer-Information-Scheme (CTIS). In the case of the TCI, we replaced the air temperature and relative humidity as the basis of the initial rating system with the physiologically equivalent temperature (PET)—a complex human biometeorological index. This modification improves the TCI’s potential to evaluate the thermal aspects of climate. The major accomplishments of this study are (a) the development of a new, PET-based rating system and its integration into the thermal sub-indices of the TCI and (b) the regionalization of the thermal components of CTIS to reflect both the thermal sensation and preference patterns of people. A 2-year-long (2011–2012) thermal comfort survey conducted in Szeged, Hungary, from spring to autumn was utilized to demonstrate the implementation of the introduced concepts. We found considerable differences between the thermal perception and preference patterns of Hungarians, with additional variations across the evaluated seasons. This paper describes the proposed methodology for the integration of the new seasonal, perception-based, and preference-based PET rating systems into the TCI, and presents the incorporation of new PET thresholds into the CTIS. In order to demonstrate the utility of the modified evaluation tools, we performed case study climate analyses for three Hungarian tourist destinations. The additional adjustments introduced during the course of those analyses include the reduction of TCI’s temporal resolution to 10-day intervals and the exclusion of nocturnal and winter periods from the investigation.

  • 18.
    Kántor, Noémi
    et al.
    University of Szeged, Szeged, Hungary.
    Gulyás, Ágnes
    University of Szeged, Szeged, Hungary.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Mikroklíma modellezés a városi közterülettervezés szolgálatában [Microclimate modeling at the service of urban public space design]2017Ingår i: Meteorológiai Tudományos Napok. 2017. November 23-24. Mikro- és mezoskálájú légköri folyamatok modellezése. Az előadások összefoglalói. / [ed] István Geresdi, Ferenc Ács, Balázs Szintai and Tamás Weidinger, Budapest, Hungary, 2017Konferensbidrag (Refereegranskat)
    Abstract [hu]

    Európa lakosságának mintegy kétharmada már most is városi környezetben él, s a városi populáció aránya 2050-re várhatóan 80% fölé fog emelkedni. Mivel a városokra jellemző többlet hőmennyiség, valamint a városok csökkent átszellőzési képessége tovább súlyosbítják a klímaváltozással járó hőmérsékletemelkedést, a – várhatóan egyre gyakoribbá, hosszabbá és intenzívebbé váló – hőhullámok hatásai különösen a városlakók egészségét veszélyeztetik. Ennél fogva a nyári hőség káros következményeinek megelőzése a várostervezés egyik kiemelt feladata. A természet- alapú megoldások (Nature-Based Solutions, NBS) egy újonnan bevezetett fogalom a környezetkutatás és környezet- gazdálkodás területén, mely a klímaváltozással járó kihívások kezelésére természetes tényezőket, illetve folyamatokat ajánl. Ebben a tanulmányban – a négyéves Nature4Cities projekt keretein belül – a fás vegetáció hőstressz-mérséklő kapacitását vettük górcső alá egyrészt terepi mérések, másrészt numerikus szimulációk segítségével.A léghőmérséklet korántsem az egyedüli paraméter az emberi szervezet hőháztartása szempontjából. Sőt, számos humán-biometeorológiai tanulmány rámutatott már a sugárzási viszonyok vezető szerepére a nyári hőterhelés kialakulásában. Éppen ezért tanulmányunkban a biometeorológiai vizsgálatok kulcsparaméterére, az átlagos sugárzási hőmérsékletre (Mean Radiant Temperature, Tmrt), illetve ennek a fás vegetáció általi mérséklésére helyeztük a hangsúlyt.Tanulmányunk első részében három, a város-biometeorológia területén gyakran alkalmazott mikroklíma modellt (RayMan, ENVI-met, SOLWEIG) hasonlítottunk össze a tekintetben, hogy mennyire képesek a Tmrt valós értékeinek szimulálására. A modellellenőrzéshez egy derült égboltviszonyokkal jellemezhető késő nyári nap humán- biometeorológiai méréssorozatának adatait használtuk fel. A 26-órás mérés során a szegedi Bartók Béla tér öt különböző pontján rögzítettük a rövid-, és hosszúhullámú sugárzási mérleg komponenseket, hogy azokból a leghitelesebb biometeorológiai eljárás szerint Tmrt-t számoljunk. A három mikroklíma-modell közül a SOLWEIG szolgáltatta a leghitelesebb eredményeket, így később ezt a modellt használtuk arra, hogy összehasonlítsuk különféle fásítási szcenáriók hőstressz-mérséklő hatását – ugyancsak a szegedi Bartók Béla téri mintaterületen. A szimulációk alapján a lombkorona transzmisszivitásának (sugárzásáteresztő képességének) változtatása kisebb, míg azonos korona-térfogat mellett a lombkorona méretének (több kis fa vs. kevesebb nagyobb fa), valamint a fák területen belüli elrendezésének változtatása (egyenletesen vs. csak az épülethomlokzatok mentén ültetett fák) jelentősebb Tmrt módosítást eredményezett.

  • 19. Kántor, Noémi
    et al.
    Gulyás, Ágnes
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Relevance of urban trees and sun shades regarding summertime heat stress reduction – a field surveys from Pécs, Hungary2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Mitigating the impact of summertime heat stress became the central issue of climate-conscious urban planning as a result of rising temperatures and continued urbanization trends. Furthermore, recent EU planning directives gave priority to nature-based solutions (NBS) and hence to re-naturing cities. Within the scope of the international Nature4Cities project fostering the use such solution, an inter- and cross-disciplinary research will be done assessing the performance of archetypal NBSs addressing different urban challenges – in this case, heat mitigation in urban environments.The objective of this particular study is to compare the effectiveness of natural and artificial shading solutions (urban trees and sun sails) in reducing summertime heat stress and enhancing outdoor thermal comfort of pedestrians. The Physiological Equivalent Temperature (PET), used as performance indicator in this study, was calculated from field data. The measurement campaign utilizing two human-biometeorological stations recorded pedestrian-level radiant flux densities from six perpendicular directions, air temperature, relative humidity and wind speed on three late-summer days. The daytime measurements were conducted at three different urban settings in Pécs, a medium-size Central-European city.Our research found that mature trees with dense canopy have the highest heat stress reduction potential and could reduce the local PET by up to 10°C. Even though artificial sun sails blocked effectively direct solar exposure, the low-hanging sun sails became the sources of long-wave radiation which made the thermal comfort conditions below them somewhat worse compared to trees. Our study demonstrates the importance of small-scale field measurements, the outcomes of which are directly applicable in the climate-adaptive design of urban spaces.

  • 20. Kántor, Noémi
    et al.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Gulyás, Ágnes
    The impact of façade orientation and vegetation on summer heat stress – measurements and simulations from a rectangular Central-European square2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Around three quarter of the European population already lives in urban areas and by 2050 this proportion isexpected to rise over 80%. Since climate change is expected to bring rising temperatures and more frequent heatwaves, mitigating the impact of extreme heat events is one of the most important issues in urban planning. Nature-Based Solutions (NBS) is a recently introduced concept in environmental research and management that promotesnature as a means to address the challenges brought about climate change. Researches of human-biometeorologydemonstrated that radiation heat load, quantified as mean radiant temperature (Tmrt), is the main source ofdaytime heat stress in summer. In European cities—especially in those with dense historic urban cores—carefullyplanned and properly maintained shade trees constitute the most effective NBS for mitigating extreme thermalconditions, while also offering several co-benefits.This study was conducted with the following two aims: (a) to assess the impact of woody vegetation anddifferent façade orientation on the radiation heat load in a complex urban setting; and (b) to evaluate the performanceof SOLWEIG, a radiation model, in reproducing the measured short- and long-wave radiation flux densities.The observation was conducted over a 26-hour long period at the rectangular Bartók Square in Szeged (Hungary)on a clear and warm late-summer day. The investigation utilized two tailor-made human-biometeorologicalstations equipped with rotatable net radiometers. The model–measurement comparison is based on data collectedfrom five locations within the square: from the center and from four sites next to the bordering façades.The measurements confirmed that on clear summer days Tmrt can reach extreme level at exposed locations(65–75C). However, shade trees are able to reduce daytime Tmrt to 30–35C. Shading SE-, S- and SW-facingfaçades and adjacent sidewalks is extremely important for the reduction of pedestrian heat stress and thus, therisk of heat stroke. When a measurement point adjacent to a facade became exposed to direct solar radiation,the radiation load increased significantly due to the additional lateral components—the reflected short-wave andthe emitted long-wave fluxes—emanating from the wall. In this respect, SOLWEIG was unable to reproducethe prolonged heat emitting effect of walls following solar exposure. Additionally, the measurement–modelcomparison revealed minor inconsistencies that originated from the model’s treatment of tree crowns: representingthem as perfectly shaped and homogeneous bodies. Due to this simplification, the observed brief penetrations ofdirect sunbeams through the canopy at most locations were not reproduced.

  • 21. Lelovics, Enikő
    et al.
    Unger, János
    Gál, Tamás
    Gál, Csilla V.
    Design of an urban monitoring network based on local climate zone mapping and temperature pattern modelling2014Ingår i: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 60, nr 1, s. 51-62Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recently developed Local Climate Zones (LCZ) classification system was initially not designed for mapping, but to classify temperature observation sites. Nevertheless, as a need arose to characterize areas based on their distinct thermal climate, utilizing LCZ classes for mapping was a logical step. The objectives of this study were (1) to develop GIS methods for the calculation of different surface parameters required for LCZ classification; (2) to identify and delineate the LCZ types within the study area using the calculated parameters; and (3) to select representative station sites for an urban monitoring network utilizing both the mapped LCZs and the modelled mean annual temperature surplus pattern in Szeged, Hungary. The study used remotely sensed data, maps and GIS databases of the city and its surroundings. The basic area of calculation was the lot area polygon, consisting of a building and its close vicinity. Adjoining polygons classified with identical or similar parameters were merged to obtain LCZs of appropriate size. As a result, 6 built LCZ types were distinguished in the studied urban area. The temperature pattern in the city was provided by an empirical model. The siting of stations took both the LCZ map and the modelled temperature pattern into account. The lampposts onto which the stations were to be mounted were determined by field surveys. The bias between the temperature pattern interpolated from the 24 stations and the initially estimated distribution by the model was found to be small. LCZ mapping is the first step in the development of urban climate maps (UCMs) that carry information on the spatial distribution and magnitude of the heat stress (thermal loads) and on the ventilation ability (dynamical potential) of different urban areas.

  • 22. Lelovics, Enikő
    et al.
    Unger, János
    Savić, Stevan
    Gál, Tamás Mátyás
    Milosevic, Dragan
    Gulyás, Ágnes
    Markovic, Vladimir
    Arsenovic, Daniela
    Gál, Csilla V
    Intra-urban temperature observations in two Central European cities, a summer study2016Ingår i: Időjárás, ISSN 0324-6329, Vol. 120, nr 3, s. 283-300Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents an urban climatological application of the urban monitoring systems – recently implemented in Szeged, Hungary and Novi Sad, Serbia – using the first set of data collected during the summer of 2014. In order to ensure a representative number and placement of stations, the selection of measurement sites was based on Local Climate Zone (LCZ) maps developed for both cities. Present paper concentrates only on the intra-urban temperature pattern characteristics expressed by the thermal reactions of the different LCZ classes in both cities. The daily temperature indices (e.g., summer days) have the highest values in the densely built up LCZs. The diurnal cycle of surplus temperatures by LCZ classes under anticyclonic weather conditions were found to be similar in the two cities with higher absolute values in the case of Novi Sad. During summer, the diurnal variation of conventional heat island intensity confirms the general knowledge that it remains positive with highest values at night, while negative values occur predominantly during the day.

  • 23. Takács, Ágnes
    et al.
    Gál, Csilla V
    Högskolan Dalarna, Akademin Industri och samhälle, Energiteknik.
    Gulyás, Ágnes
    Kiss, Márton
    Kántor, Noémi
    Radiation conditions at a Central European square in a hot summer day, a case study from Szeged, Hungary2017Ingår i: 97th Annual Meeting of the American Meteorological Society (AMS) jointly with the 13th Symposium on the Urban Environment, Seattle, WA, 2017Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In the light of sustained urbanization and rising temperature trends, mitigating the impact of extreme heat events is a pressing urban planning issue. Radiation heat load, quantified as mean radiant temperature (Tmrt), has been identified as the main source of summer heat stress. Several studies ascertained that Tmrt is the key factor driving human thermal comfort in outdoor urban places. Shading that reduces radiation heat load (Tmrt) is the most effective means to mitigate heat stress in outdoor public places, which offer a venue for leisure, recreation and for the social life of residents. Nonetheless, the small-scale thermal conditions of urban places are not only governed by shade trees and greenery, but also by buildings and paved surfaces. The aim of this study is twofold. First, it assesses the impact of differently oriented street facades with varying solar exposure on the human radiation balance at a medium-sized square in a mid-latitude city. Second, it evaluates the performance of popular, freely available microclimate and radiation models in deriving Tmrt values. The well-vegetated, rectangular Bartók square was selected in Szeged, Hungary to calculate various radiation parameters using three numerical simulation models (ENVI-met, SOLWEIG and RayMan). The derived parameters (radiation flux densities from different directions, as well as Tmrt) are compared with corresponding values obtained from detailed on-site measurements. The field data are collected as part of a 24-hour long radiation measurement utilizing the six-directional method, where a set of pyranometers and pyrgeometers are used to record short- and long-wave flux densities from six perpendicular directions (from above, from below as well as from the four cardinal points). The model-measurement comparison is based on hourly data from five locations within the square: from the center and from near the four bordering street facades of the rectangular square. Our initial results indicate that besides direct solar radiation, the temperatures of artificial surfaces (e.i. of building walls and pavements) strongly influences the human radiation balance: the increased temperature of surrounding surfaces increases the amount of emitted long-wave radiation and thus, reduces the amount a person is able to dissipate. Investigations like ours are necessary both for the advancement of our filed in general, and for the development of numerical models in particular. Models are simplifications of reality and thus they introduce a certain degree of idealization: trees are never as perfectly shaped or have a homogeneous crown transmissivity and leaf area index (LAI) in the reality, neither do surface parameters are as uniform as frequently assumed by models. All these differences influence model results to a certain degree. Therefore, the ideal outdoor thermal conditions that practitioners often plan for from behind their desks are likely to be worse in reality. Identifying the strengths and weaknesses of different models and revealing how they compare to reality is essential for both scientists and urban planners, since they all need to understand and acknowledge the limitations of the numerical approach.

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