Relevance of Thermal Indices for the Assessment of the Urban Heat Island (original) (raw)
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Comparison of different methods for the assessment of the urban heat island in Stuttgart, Germany
International Journal of Biometeorology, 2014
This study of the urban heat island (UHI) aims to support planning authorities by going beyond the traditional way of urban heat island studies. Therefore, air temperature as well as the physiologically equivalent temperature (PET) were applied to take into account the effect of the thermal atmosphere on city dwellers. The analysis of the urban heat island phenomenon of Stuttgart, Germany, includes a longterm frequency analysis using data of four urban and one rural meteorological stations. A (high resolution map) of the UHI intensity and PET was created using stepwise multiple linear regression based on data of car traverses as well as spatial data. The mapped conditions were classified according to the long-term frequency analysis. Regarding climate change, the need for adaptation measures as urban greening is obvious. Therefore, a spatial analysis of quantification of two scenarios of a chosen study area was done by the application of a micro-scale model. The nocturnal UHI of Stuttgart is during 15 % stronger than 4 K in the city center during summer when daytime heat stress occurs during 40 %. A typical summer condition is mapped using statistical approach to point out the most strained areas in Stuttgart center and west. According to the model results, the increase in number of trees in a chosen area (Olga hospital) can decrease PET by 0.
Ecological Indicators, 2012
Urban heat islands (UHIs) describe the phenomenon of altered temperatures that occur in urban areas when compared to their rural surroundings. UHIs influence human well-being, human health and the city as an ecological niche. UHIs can be quantified with meteorological ground measurements of air temperatures or with remotely sensed land surface temperatures (surface urban heat island). Both approaches have advantages and disadvantages and are rarely combined. Further, within these approaches, different indicators for quantifying the UHIs are used. In this methodological study, we (1) combined data on land surface and air temperatures, (2) enriched the debate by suggesting the application of indicators for the two distinct data sets and (3) systematically quantified indicators of all approaches for the city of Leipzig, Germany. A relationship between the land surface and air temperatures was established. However, the results for the single indicators showed that the absolute values of the detected UHI in Leipzig depend on the selected indicator and the data set used. The main conclusion for future studies on UHIs is to use several UHI indicators in parallel to acknowledge the uncertainty of measuring the UHI using a single indicator and either ground measurements or remote sensing.
Urban Climate, 2014
The spatial and temporal differences of climate, urban heat island and future conditions were assessed for Stuttgart, a city located in complex topography in Southwest Germany. The present and future urban climate conditions were analysed using hourly measured data from 2000 to 2011 of 5 measuring stations and data from regional climate simulations. The urban heat island intensity was quantified applying thermal indices as Physiologically Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) and compared to weather type classifications. In Stuttgart, wind speed was mostly less than 3 ms À1 , the wind roses were very inconsistent and local wind could be clearly observed. The average annual urban heat island of air temperature was between 0.3 K in the suburb areas to 2 K in the city centre and the maximum up to 12 K. The assessed urban heat island with PET was in average 3.3 K and maximum around 20 K. Based on regional climate simulation we found that the amount of days with heat stress (PET P 35°C) is estimated to increase by about 17 days until the end of the 21st century. Urban heat island and intra-urban variability were most obvious using thermal indices rather than air temperature.
Analysis of micro climatic variations and the urban heat island phenomenon in the city of Vienna
"Metropolitan areas are dealing with very diverse microclimatic situations influenced by different morphologies, structures, and materials of the built environment. Moreover, it has been proven that urban areas show significantly higher temperatures than rural surroundings. This is referred to as the urban heat island phenomenon (UHI). Furthermore, the UHI effect is directly related to (and worsened by) the climate change phenomena, where it is expected that an increase of the average temperature has a stronger and immediate effect on the health of people living in cities. Additionally higher air temperatures have a direct effect on the energy consumption due to increased use of air conditioning. In this context this paper presents results of an ongoing research project which investigates the urban heat island phenomena in the Central European area. Specifically, this paper analyzes the urban heat island phenomenon and microclimate conditions looking at various locations in the city of Vienna. Towards this end, existing weather stations in urban as well as rural locations have been selected and the data has been analyzed and compared with regard to the surrounding area in terms of density, surface characteristics, and vegetation. Specifically, the urban heat island intensity, the diurnal variation, and the seasonal trend of temperature differences were investigated. Based on the analysis, the main contributing factors and typical characteristic patterns will be discussed."
Urban measures for hot weather conditions in a temperate climate condition: A review study
Renewable and Sustainable Energy Reviews, 2017
This paper discusses the effects of urban design and meteorological parameters on thermal comfort for pedestrians at street level. Results from other studies do not allow an objective comparison of the effectiveness of climate adaptation measures. These results are based on different measurement and modelling methods, they are given in various comfort indicators and they are studied in a specific urban context, climate and weather condition. This study presents the relative effects of design measures based on identical input parameters and one simulation method. In the analysis of these effects the three-dimensional model ENVI-met is used to calculate microclimatic changes. Additionally, the study uses various methods to show this model is appropriate in this context. For the assessment of human comfort, the simulation outcomes are then translated into the comfort indicator physiological equivalent temperature (PET). The PET is an outstanding index for this study because it links climate aspects and the physiology of the human body. Model calculations are run for a typical heatwave day in the temperate climate of the Netherlands. The urban design measures and meteorological parameters start out from an open field, followed by a single building and gradually increasing complexity to varying wind speed and direction, a different building form and vegetation. The results show that urban design and meteorological parameters influencing wind speed and mean radiant temperature highly influence thermal comfort on a very local level. While parameters that influence air temperature and humidity have limited impact on thermal comfort, but their influence affects a larger area.
Journal of Geophysical Research, 2011
1] This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of small to large cities and villages in the Netherlands. To date, this subject has not been substantially studied in the Netherlands, since it has a relatively mild oceanic (Cfb) climate and impact was assumed to be minor. To fill this knowledge gap, this paper reports on observations of a selected network of reliable hobby meteorologists, including several in The Hague and Rotterdam. A number of alternative measures were also used to quantify UHI, i.e., the generalized extreme value distribution and return periods of UHI and adverse human comfort; its uncertainties were estimated by the statistical method of bootstrapping. It appeared essential to distinguish observations made at roof level from those made within the urban canyon, since the latter related more closely to exposure at pedestrian level and to urban canyon properties in their close neighborhood. The results show that most Dutch cities experience a substantial UHI, i.e., a mean daily maximum UHI of 2.3 K and a 95 percentile of 5.3 K, and that all cities experience a shadow effect in the morning when cities remain cooler than the rural surroundings. Also, an evident relation between the median of the daily maximum UHI and its 95 percentile was discovered. Furthermore, the 95 percentile of the UHI appears well correlated with population density. In addition, we find a significant decrease of UHI and the percentage of surface area covered by green vegetation, but the relation with open water remains unclear.
International Journal of Architectural Engineering Technology, 2015
Unlike most of the Brazilian hot-humid cities, subtropical Curitiba experiences thermal discomfort due to cold during most of the year, with the coldest air temperature occurring in winter. Due to rapid urbanization, the Metropolitan Area has been faced with critical environmental problems. Urban microclimate patterns exhibit considerable variability; particular areas of the city alternate between cool islands and heat islands, resulting in different outdoor thermal comfort levels. The objective of this work is twofold: 1) to characterize intra-urban air temperature differences and their impact on outdoor thermal comfort in Curitiba; 2) to assess the yearlong Urban Heat Island (UHI) effect and its effect on indoor thermal comfort levels. For that, a series of independent measurements and field monitoring campaigns, both outdoors and indoors, were analyzed. Results point to a great variability in intra-urban temperature differences and derived outdoor comfort levels. With regard to predicted UHI effects in low-cost dwellings, indoor comfort due to heat was found to prevail over the year; the 'net effect' between heat stress in summer and cold stress in winter point towards a prevalence of heat stress indoors.
Urban heat island Outdoor thermal comfort Physiologically equivalent temperature (PET) Intra-urban variability Land use fractions Urban geometry a b s t r a c t This paper reports on temporal and spatial variability of local climate and outdoor human thermal comfort within the Rotterdam agglomeration. We analyse three years of meteorological observations (2010e2012) from a monitoring network. Focus is on the atmospheric urban heat island (UHI); the difference in air temperature between urban areas and rural surroundings. In addition, we calculate the Physiologically Equivalent Temperature (PET) which is a measure of thermal comfort. Subsequently, we determine the dependency of intra-urban variability in local climate and PET on urban land-use and geometric characteristics. During a large part of the year, UHI-intensities in densely built areas can be considerable, under calm and clear (cloudless) weather conditions. The highest maximum UHI-values are found in summer, with 95-percentile values ranging from 4.3 K to more than 8 K, depending on the location. In winter, UHIintensities are generally lower. Intra-urban variability in maximum UHI-intensity is considerable, indicating that local features have an important influence. It is found to be significantly related to building, impervious and green surface fractions, respectively, as well as to mean building height.
Atmospheric conditions and human thermal comfort in urban areas
2000
Climate and air quality must be taken into account in urban and regional planning at regional level in a manner which is relevant to human health and well being. In view of the combined effects of atmospheric conditions on man, thermal, air quality and actinic factors are particularly important in preventive planning.