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Helmut Mayer

Bio: Helmut Mayer is an academic researcher from University of Freiburg. The author has contributed to research in topics: Beech & Fagus sylvatica. The author has an hindex of 38, co-authored 91 publications receiving 8389 citations. Previous affiliations of Helmut Mayer include Ludwig Maximilian University of Munich & University of Melbourne.


Papers
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Journal ArticleDOI
TL;DR: The physical basis of the RayMan model, which simulates the short- and long-wave radiation flux densities from the three-dimensional surroundings in simple and complex environments, is presented.
Abstract: Short- and long-wave radiation flux densities absorbed by people have a significant influence on their energy balance. The heat effect of the absorbed radiation flux densities is parameterised by the mean radiant temperature. This paper presents the physical basis of the RayMan model, which simulates the short- and long-wave radiation flux densities from the three-dimensional surroundings in simple and complex environments. RayMan has the character of a freely available radiation and human-bioclimate model. The aim of the RayMan model is to calculate radiation flux densities, sunshine duration, shadow spaces and thermo-physiologically relevant assessment indices using only a limited number of meteorological and other input data. A comparison between measured and simulated values for global radiation and mean radiant temperature shows that the simulated data closely resemble measured data.

1,334 citations

Journal ArticleDOI
TL;DR: The physiological equivalent temperature (PET) as discussed by the authors is a thermal index derived from the human energy balance, which is well suited to the evaluation of the thermal component of different climates and can be presented graphically or as bioclimatic maps.
Abstract: The physiological equivalent temperature, PET, is a thermal index derived from the human energy balance. It is well suited to the evaluation of the thermal component of different climates. As well as having a de- tailed physiological basis, PET is preferable to other thermal indexes like the predicted mean vote because of its unit (°C), which makes results more comprehensible to urban or regional planners, for example, who are not so familiar with modern human-biometeorological termi- nology. PET results can be presented graphically or as bioclimatic maps. Graphs mostly display the temporal behaviour of PET, whereas spatial distribution is speci- fied in bioclimatic maps. In this article, some applica- tions of PET are discussed. They relate to the evaluation of the urban heat island in cities in both temperate cli- mates and warm climates at high altitude. The thermal component of the microclimate in the trunk space of a deciduous forest is also evaluated by PET. As an exam- ple of the spatial distribution of PET, a bioclimatic map for Greece in July (Mediterranean climate) is presented.

925 citations

Journal ArticleDOI
TL;DR: In this article, a hot summer day, biometeorological measurements were performed simultaneously in three different urban structures within the city of Munich and in the trunk space of a nearby tall spruce forest.
Abstract: On July 29, 1985, a hot summer day, biometeorological measurements were performed simultaneously in three different urban structures within the city of Munich and in the trunk space of a nearby tall spruce forest. Based on the results of these experiments the following thermophysiologically relevant biometeorological indices were calculated: Predicted mean vote, skin wettedness and physiologically equivalent temperature. These three indices are derived from different models for the human energy balance. They allow the assessment of the thermal components of the microclimates at the selected sites with regard to application in urban planning. The results quantitatively show the great heat stress in the urban structure “street canyon, exposed to south”, whereas in the “trunk space of the tall spruce forest” there is nearly an optimal climate even on hot summer days. Between these extremes the results for “street canyon, exposed to north” show a little higher heat load than for “backyard with trees”.

803 citations

Journal ArticleDOI
TL;DR: In this article, the contribution of street design, i.e. aspect ratio (or height-to-width ratio, H / W ) and solar orientation, towards the development of a comfortable microclimate at street level for pedestrians is discussed.

798 citations

Journal ArticleDOI
TL;DR: In this paper, a qualitative overview of the air quality of the world's megacities is given, and a qualitative assessment of air pollution in cities is shown, as well as a qualitative analysis of air quality conditions in other cities.

503 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a new climatic drought index, the standardized precipitation evapotranspiration index (SPEI), is proposed, which combines multiscalar character with the capacity to include the effects of temperature variability on drought assessment.
Abstract: The authors propose a new climatic drought index: the standardized precipitation evapotranspiration index (SPEI). The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a log-logistic probability distribution. Mathematically, the SPEI is similar to the standardized precipitation index (SPI), but it includes the role of temperature. Because the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer drought severity index (sc-PDSI). Time series of the three indices were compared for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions, only the sc-PDSI and SPEI identified an...

5,088 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used systematic review methodology to evaluate available evidence on whether greening interventions, such as tree planting or the creation of parks or green roofs, affect the air temperature of an urban area.

1,822 citations

Journal ArticleDOI
TL;DR: The physiological equivalent temperature (PET) is defined as the air temperature at which the heat budget of the human body is balanced with the same core and skin temperature under the complex outdoor conditions to be assessed, and enables a layperson to compare the integral effects of complex thermal conditions outside with his or her own experience indoors.
Abstract: With considerably increased coverage of weather information in the news media in recent years in many countries, there is also more demand for data that are applicable and useful for everyday life. Both the perception of the thermal component of weather as well as the appropriate clothing for thermal comfort result from the integral effects of all meteorological parameters relevant for heat exchange between the body and its environment. Regulatory physiological processes can affect the relative importance of meteorological parameters, e.g. wind velocity becomes more important when the body is sweating. In order to take into account all these factors, it is necessary to use a heat-balance model of the human body. The physiological equivalent temperature (PET) is based on the Munich Energy-balance Model for Individuals (MEMI), which models the thermal conditions of the human body in a physiologically relevant way. PET is defined as the air temperature at which, in a typical indoor setting (without wind and solar radiation), the heat budget of the human body is balanced with the same core and skin temperature as under the complex outdoor conditions to be assessed. This way PET enables a layperson to compare the integral effects of complex thermal conditions outside with his or her own experience indoors. On hot summer days, for example, with direct solar irradiation the PET value may be more than 20 K higher than the air temperature, on a windy day in winter up to 15 K lower.

1,674 citations

Journal ArticleDOI
TL;DR: The role du couvert dans les echanges avec l'atmosphere is rappele puis integre dans l'analyse des reductions de bilan d'eau and de carbone in 2003 dus a regulation stomatique as discussed by the authors.
Abstract: La secheresse exceptionnelle de 2003 a ete l'occasion de faire le point de nos connaissances sur les mecanismes ecophysiologiques permettant aux arbres de traverser un tel evenement climatique extreme. L'analyse a ete conduite a l'echelle de l'arbre et du peuplement, tandis que l'intensite de la secheresse a ete quantifiee a l'aide d'un calcul de bilan hydrique sur neuf sites forestiers europeens contrastes du reseau CARBOEUROPE. Le role du couvert dans les echanges avec l'atmosphere est rappele puis integre dans l'analyse des reductions de bilan d'eau et de carbone en 2003 dus a la regulation stomatique. Les caracteristiques du complexe sol-racine, important a la fois pour l'acces a la ressource et a l'efficience de son absorption, constituent un des premiers traits d'adaptation a la secheresse. La reponse et les adaptations des especes ont surtout ete analysees en termes de diversite inter-specifique de fonctionnement hydraulique et du couplage entre proprietes hydrauliques et regulation stomatique. Enfin, nous discutons l'hypothese selon la quelle les dysfonctionnements hydrauliques ou les deficits de mise en reserve sont impliques dans les reactions differees de croissance, de developpement, d'induction de deperissement. Par exemple, des mesures de reserves glucidiques dans les troncs de chenes menees en fin d'ete 2003 ont permis de predire l'etat des couronnes des arbres au printemps 2004. Les faibles taux d'amidon etaient associes a une forte mortalite de branches et de jeunes pousses.

1,553 citations

Journal ArticleDOI
TL;DR: In this paper, the authors explore the important role that the green infrastructure of a city can play in adapting for climate change and present output from energy exchange and hydrological models showing surface temperature and surface runoff in relation to green infrastructure under current and future climate scenarios.
Abstract: The urban environment has distinctive biophysical features in relation to surrounding rural areas. These include an altered energy exchange creating an urban heat island, and changes to hydrology such as increased surface runoff of rainwater. Such changes are, in part, a result of the altered surface cover of the urban area. For example less vegetated surfaces lead to a decrease in evaporative cooling, whilst an increase in surface sealing results in increased surface runoff. Climate change will amplify these distinctive features. This paper explores the important role that the green infrastructure, i.e. the greenspace network, of a city can play in adapting for climate change. It uses the conurbation of Greater Manchester as a case study site. The paper presents output from energy exchange and hydrological models showing surface temperature and surface runoff in relation to the green infrastructure under current and future climate scenarios. The implications for an adaptation strategy to climate change in the urban environment are discussed.

1,520 citations