Solar permeability of different tree species in Szeged, Hungary

Abstract

The heat stress modification capacity of urban trees is widely acknowledged and makes these natural landscape elements very important in the field of climate conscious urban planning. Many studies proved that shading, i.e. the reduction of direct solar radiation is the most effective way to moderate summer heat stress under Central European climatic conditions. The investigation aims at determining the transmissivity of four tree species that occur frequently in Hungarian cities: Sophora japonica, Tilia cordata, Celtis occidentalis and Aesculus hippocastanum. In order to accomplish that, a systematic radiation measurement campaign was carried out in the South-Hungarian city of Szeged, from early summer (foliated condition of trees) to late autumn (nearly leafless condition). Short-wave radiation from the upper hemisphere was measured with Kipp & Zonen pyranometers under carefully selected tree specimens (transmitted radiation), as well as on a roof station free from sky obstruction (actual value of global radiation). The calculated transmissivity values varied greatly with the seasonal status of the canopy (the median value of transmissivity increased from 0.03 to 0.47 in case of A. hippocastanum), and we found considerable inter-species differences too, evidencing that solar permeability depends on the amount of leaves, leaf density and other tree crown-related characteristics.

Biological Flora of the British Isles:Aesculus hippocastanum

“…City trees in south‐east Hungary transmitted just 7 ± 10% ( SD ) of full sunlight in mid‐summer, increasing to 25 ± 14% at the end of September when half leafless due to the start of autumn abscission. At this point in autumn, there was more shade below horse‐chestnut than cast by Styphnolobium japonicum (L.) Schott (= Sophora japonica ) (15 ± 8%) and Tilia cordata (12 ± 13%) that were losing leaves, but less than Celtis occidentalis that was not yet shedding leaves (Takács, Kiss, Gulyás, Tanács, & Kántor, ), suggesting that horse‐chestnut maintains its deep shade comparatively late into autumn, increasing its competitiveness. Certainly in most urban areas around Europe, little will grow beneath a group of horse‐chestnut trees.…”

The Maturing Interdisciplinary Relationship between Human Biometeorological Aspects and Local Adaptation Processes: An Encompassing Overview

“…Adjacently to these T a studies, aspects of urban vegetation as a tool address and regulate human thermal comfort in urban environments through non-temperature factors have also been discussed extensively. Such factors included the direct role urban tree crowns reducing the amount of radiation reaching pedestrian levels [192][193][194][195][196]. Subsequently, this was followed by studies which focused upon assessments that included non-temperature dynamics through the use of human biometeorological models and indices in both IS studies (Table 6) and PCI studies (Table 7).…”

Trees as a Shading System for Streets on the East–West Axis: Computer Simulations for the Selected Geometrical Proportions of Building Developments in Humid Continental Climate

“…According to research by Konarska et al [4], radiation transmittance for the deciduous trees tested in the full foliage period amounts to 8.8%-27.5%.) For instance, studies by Givoni [5], Takács et al [6], Ali-Toudert and Mayer [3], or Shashua-Bar and Hoffman [7] draw attention to the importance of highrise greenery as shading elements in the street space. Moreover, according to Mayer and Ali-Toudert [1], shading should be seen as the most effective climate function trees serve in improving thermal comfort.…”