János Unger

Connection between urban heat island and sky view factor approximated by a software tool on a 3D urban database

This study provides a review on methods of Sky View Factor (SVF) determination and intra-urban surface geometry-air temperature relationship. Then, a software-based method of SVF estimation from a 3D database, describing urban surface elements, is applied. Finally, related investigations in Szeged and importance of the results obtained are discussed. Previous investigations were limited to only specific urban parts or some canyons and used small numbers of sites and few occasions of measurements. This study utilises a large number of areal means of SVF and temperature related to a large sample area and based on numerous measurements. Our investigation reveals a strong relationship between these variables. Thus, surface geometry is a significant determining factor of the temperature distribution if the selected scale is appropriate. Therefore, investigations of sufficient number of appropriate-sized areas, covering large parts of a city, are needed to draw well-established conclusions on the studied relationship.

The most problematic variable in the course of human-biometeorological comfort assessment - The mean radiant temperature

This paper gives a review on the topic of the mean radiant temperature Tmrt, the most important parameter influencing outdoor thermal comfort during sunny conditions. Tmrt summarizes all short wave and long wave radiation fluxes reaching the human body, which can be very complex (variable in spatial and also in temporal manner) in urban settings. Thermal comfort researchers and urban planners need easy and sound methodological approaches to assess Tmrt. After the basics of the Tmrt calculation some of the methods suitable for obtaining Tmrt also in urban environments will be presented.. Two of the discussed methods are based on instruments which measure the radiation fluxes integral (globe thermometer, pyranometer-pyrgeometer combination), and three of the methods are based on modelling the radiation environment with PC software (RayMan, ENVI-met and SOLWEIG).

Subjective estimation of thermal environment in recreational urban spaces-Part 1: Investigations in Szeged, Hungary

During two investigation periods in transient seasons (14 weekdays in autumn 2009 and 15 weekdays in spring 2010) 967 visitors in two inner city squares of Szeged (Hungary) were asked about their estimation of their thermal environment. Interrelationships of subjective assessments—thermal sensation, perceptions and preferences for individual climate parameters—were analyzed, as well as their connections with the prevailing thermal conditions [air temperature, relative humidity, wind velocity, mean radiant temperature and physiologically equivalent temperature (PET)]. Thermal sensation showed strong positive relationships with air temperature and solar radiation perception, while wind velocity and air humidity perception had a negative (and weaker) impact. If a parameter was perceived to be low or weak, then it was usually desired to be higher or stronger. This negative correlation was weakest in the case of humidity. Of the basic meteorological parameters, Hungarians are most sensitive to variations in wind. Above PET = 29°C, people usually prefer lower air temperature and less solar radiation. The temperature values perceived by the interviewees correlated stronger with PET, but their means were more similar to air temperature. It was also found that the mean thermal sensation of Hungarians in transient seasons depends on PET according to a quadratic function (R2 = 0.912) and, consequently, the thermal comfort ranges of the locals differ from that usually adopted.

Subjective estimations of thermal environment in recreational urban spaces—Part 2: international comparison

The present paper is the second part of our study in which we compare the results obtained in Szeged (Hungary) with those achieved through earlier outdoor thermal comfort projects based on simultaneous questionnaire surveys and on-site meteorological measurements. The main characteristics of the selected studies—conducted in Hungary, Sweden, Portugal, Canada, Taiwan and across Europe in the frame of project RUROS—are reviewed, emphasizing the common features and also the discrepancies in the applied methodology. We discuss their potential effects on the evolution and interpretation of the results concerning the subjective assessment of the thermal environment. Another aspect of the comparison focuses on the regional climatic differences naturally ensuing from the various locations, which left their marks on the results related to both physiological acclimatization and mental adaptation. The compared results of different studies include correlation coefficients expressing interrelationships between the different aspects of subjective estimations (thermal sensation, perceptions, preferences) and also between subjective assessments and the corresponding meteorological parameters. We compare neutral temperatures (expressed in physiological equivalent temperature, PET) which arose for Taiwan and Hungary, as well as thermal sensation zones for local inhabitants. Subjectively assessed temperature values of Sweden and Hungarians are analyzed according to the measured air temperature. According to our experiences the methodology should be standardized for the level of field surveys and also for the level of data processing in order to make the data collected in different locations comparable.

Modelling of the Annual Mean Urban Heat Island Pattern for Planning of Representative Urban Climate Station Network

The spatial distribution of the annual mean urban heat island (UHI) intensity pattern was analysed for the medium-sized city Novi Sad, Serbia, located on the low and flat Great Hungarian Plain. The UHI pattern was determined by an empirical modelling method developed by (Balazs et al. 2009). This method was based on datasets from urban areas of Szeged and Debrecen (Hungary). The urban study area in Novi Sad (60 km2) was established as a grid network of 240 cells (0.5 km ×0.5 km). A Landsat satellite image (from June 2006) was used in order to evaluate normalized difference vegetation index and built-up ratio by cells. The pattern of the obtained UHI intensity values show concentric-like shapes when drawn as isotherms, mostly increase from the suburbs towards the inner urban areas. Results of this thermal pattern and determination of one of the local climate classification systems were used for recommending 10 locations for representative stations of an urban climate network in Novi Sad.

Adjustment of the thermal component of two tourism climatological assessment tools using thermal perception and preference surveys from Hungary

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.

Airborne surface temperature differences of the different Local Climate Zones in the urban area of a medium sized city

This paper presents a case study about the surface temperature characteristics of the different Local Climate Zones (LCZ) in Szeged, Hungary. For the evaluation we apply high resolution surface temperature data acquired by a low-cost small-format digital imaging system, measured in early night hours. The map of Local Climate Zones for the study area is derived by an automatic GIS method for LCZ classification. The results show that the different LCZ classes have different surface temperature characteristics. Among the densely populated LCZ classes the open low-rise has the lowest surface temperature, thus it is can be the most favorable urban built-up type if the aim is the decrease the effect of the urban heat load.

Application of Microclimate Modelling and Onsite Survey in Planning Practice Related to an Urban Micro-Environment

Numerical simulations of human thermal comfort conditions were carried out by means of the urban microclimate model ENVI-met in a popular children’s playground located in Szeged, Hungary. Bioclimatic conditions were quantified by the Physiologically Equivalent Temperature (PET). Based on the PET values, thermal stress maps were created in two different periods of typical summer and autumn days. The study aims to reveal the seasonal and diurnal spatial patterns of the simulated thermal conditions and thus the degree of heat stress in different parts of the playground. Furthermore, we analysed the momentary spatial distributions of the visitors triggered by the microclimatic conditions of the area. According to the simulation, remarkable differences in the thermal conditions were found depending on the sun elevation and the resulting shaded conditions as well as the radiation of the heated surfaces. The spatial distribution of the visitors seems to be highly influenced by the patterns of the thermal conditions but the location and the preference of the children’s playground equipment also affects it. In order to reveal the possible causes of the people’s behaviour, an onsite questionnaire survey was conducted on their opinions and possible modification requirements related to the design of the playground.

The impact of façade orientation and woody vegetation on summertime heat stress patterns in a Central-European square : comparison of radiation measurements and simulations

Increasing summertime air temperature deteriorates human health especially in cities where the warming tendency is exacerbated by urban heat island. Human-biometeorological studies shed light on th ...