Differences in the thermal bioclimatic conditions on the urban and rural areas in a southern Hungarian city (Szeged)

The aim of this study is to compare the bioclimatic situation of a city and the surrounding rural area on the example of a Southern Hungarian city (Szeged). To examine the frequency of the one hour averages of the PET index, it is shown that due to the strong direct radiation a strong or extreme heat stress values has 1.1 % higher occurrence in the rural areas compared to the urban ones. But considering the PET averages through the whole examined time period, it is 14 % higher in the urban areas. This effect is more pronounced in summer, when daytime with extreme heat stress is followed by night with 7-8 °C higher PET values in the city. During these times, the human body cannot regenerate in the nights before the repeated extreme heat stress occurs again during daytime. This makes the urban bioclimatic conditions (in summer, especially during heat wave) more demanding, compared to the rural ones

Different aspects in the quantification of the Sky View Factor in complex environments.

This paper examines potential applications of the sky view factor (SVF) regarding two- or threedimensional sites. First, the concepts of the radiation budget, Lambert's cosine law and hemispherical description of radiating of en vironments are introduced and connected to the sky view factor. Based on a comparison between different models and methods which calculate the SVF, the paper then focuses on two different kinds of SVFcalculation depending on the type of analyzed site. It is assumed that in case the point of interest represents a flat, two-dimensional area, it makes sense to include the cosine law whereas in case the point of interest represents a solid three-dimensional object the application of Lambert's law could have to be applied in another way. It is shown that the inclusion or exclusion of the cosine law results in different SVF values. It is concluded that depending on the type of surveyed area, the application of a 2D- or 3D-sky view factor should be considered in order to get a better approximation of the radiation fluxes

The impact of increasing urban surface albedo on outdoor summer thermal comfort within a university campus

The impact of increasing urban surface albedo on outdoor thermal comfort was studied in two phases: Firstly, the thermal conditions of three locations with different ground surface materials were compared. The study used CFD modelling followed by a measurement campaign to validate the control simulation. It was observed that the physiological equivalent temperature (PET as the outdoor thermal comfort index) in the campus park (covered with grass) was 11.0 °C lower than the parking lot (paved with concrete) at 16:00 CET. As the next step, the albedo of the roofs and walls were increased from 0.2 (control) to 0.3, 0.4, 0.5 and 0.6. It was found that increasing the albedo made the open space of the courtyard uncomfortable due to the higher reflectivity of high-albedo materials. An increase of every 0.1 albedo of the surfaces led to 1.2 °C higher mean radiant temperature, and consequently, 0.8 °C higher PET. The study also showed that the increase of albedo radiated more sun to the ground surface. This increased average ground surface sensible heat flux (6.7 W/m2) and surface temperature (0.4 °C) during the day. This finding shows that the position and orientation of high albedo materials can significantly affect pedestrians' thermal comfort in urban open spaces

The relationship between built-up areas and the spatial development of the mean maximum urban heat island in Debrecen, Hungary

The climate of built-up regions differs significantly from rural regions and the most important modifying effect of urbanization on local climate is the urban temperature excess, otherwise called the urban heat island (UHI). This study examines the influence of built-up areas on the near-surface air temperature field in the case of the medium-sized city of Debrecen, Hungary. Mobile measurements were used under different weather conditions between March 2002 and March 2003. Efforts concentrated on the determination of the spatial distribution of mean maximum UHI intensity with special regard to land-use features such as built-up ratio and its areal extensions. In both (heating and non-heating) seasons the spatial distribution of the UHI intensity field showed a basically concentric shape with local anomalies. The mean maximum UHI intensity reaches more than 2.0 degrees C (heating season) and 2.5 degrees C (non-heating season) in the centre of the city. We established the relationship between the above-mentioned land-use parameters and mean maximum UHI intensity by means of multiple linear regression analysis. As the measured and predicted mean maximum UHI intensity patterns show, there is an obvious connection between the spatial distribution of urban thermal excess and the land-use parameters examined, so these parameters play a significant role in the development of the strong, UHI intensity field over the city. Copyright (c) 2005 Royal Meteorological Society

Selected examples of bioclimatic analysis applying the physiologically equivalent temperature in Hungary

Összefoglalás : Cikkünkben bioklimatológiai elemzést végzünk az ún. Fiziológiailag Equivalens Hőmérséklet (PET) index felhasználásával először Magyarország egész területén (1 km-es felbontású bioklíma térkép segítségével). A bioklíma térképek a PET index térbeli eloszlását mutatják Magyarországon egy téli (február) és egy nyári (augusztus) hónapban. Majd két szinoptikai állomás (Szombathely és Sopron) 1996 és 1999 között rögzített adataiból számított PET értékek alapján részletes elemzésben hasonlítjuk össze a két város főbb bioklimatológiai jellegzetességeit. Summary : In this study, maps were created that show the geographical distribution of Physiologically Equivalent Temperature (PET) values in February and August for the area of Hungary, with a resolution of 1 km. For the further analysis of the thermal bioclimate, data of the synoptical stations of Szombathely and Sopron, recorded from 1996 to 1999, has been used. This study provides a detailed analysis and comparison of the bioclimatic properties of these locations

Influence of ground surface characteristics on the mean radiant temperature in urban areas

The effect of variations in land cover on mean radiant surface temperature (Tmrt) is explored through a simple scheme developed within the radiation model SOLWEIG. Outgoing longwave radiation is parameterised using surface temperature observations on a grass and an asphalt surface, whereas outgoing shortwave radiation is modelled through variations in albedo for the different surfaces. The influence of surface materials on Tmrt is small compared to the effects of shadowing. Nevertheless, altering ground surface materials could contribute to a reduction on Tmrt to reduce the radiant load during heat-wave episodes in locations where shadowing is not an option. Evaluation of the new scheme suggests that despite its simplicity it can simulate the outgoing fluxes well, especially during sunny conditions. However, it underestimates at night and in shadowed locations. One grass surface used to develop the parameterisation, with very different characteristics compared to an evaluation grass site, caused Tmrt to be underestimated. The implications of using high resolution (e.g. 15 minutes) temporal forcing data under partly cloudy conditions are demonstrated even for fairly proximal sites

Pilot actions in European cities - Stuttgart

The field of urban climatology has a long tradition in Stuttgart. It exists as discipline in Stuttgart since 1938. Stuttgart was the first city to establish its own Department of Climatology to research ways of improving the flow of fresh air into the city and to reduce thermal stress in most populated city districts. The specialist department of Urban Climatology, within the Environmental Protection Office, deals with tasks relating to environmental meteorology within the scope of air pollution control and also relating to urban and global climate protection. So in Stuttgart the urban heat island phenomenon (UHI) is studied for several decades, leading to a high level understanding of the UHI and the problems which it causes. The UHI causes an increase in air temperatures and thermal stress, that are identified as most negative impacts on human health and urban living. In the view of global climate change and the predicted temperature rise for the Stuttgart region of 1.5–2 K in this century, the negative impacts of UHI on human health and urban living will become more problematic in the future. According to the results of climate models the frequency of very hot days is expected to jump by nearly 30 % at the end of the century. The rising temperatures due to the global climate change in combination with the temperature shift as a result of the UHI will intensify the heat stress in urban areas, that leads to a significant increasing risk to human health, in particular to the very young and elderly. Not least due its importance for the human health and the quality of urban life in Stuttgart, the UHI is focussed by urban planners and is noticed by the future development of the city. Within the pilot action study in Stuttgart several measure for reducing the UHI and the impacts on urban living and human health are analysed by the use of micro-scale and macro-scale simulations. With the help of these analysis realisable measure are selected. The most useful measures are implemented into a developmoutline plan for the redevelopment of the city district Stuttgart-West by the municipal urban planners