Trees as Indicators of the Urban Heat Island
Final Report Abstract
The DFG-funded project "Trees as Indicators for the Urban Heat Island (BIWi)" aimed to examine chronologies of annual ring-width series (ARWC) in Berlin to determine whether the ARWCs of different locations in Berlin reflect the degree of urbanization and thus a signal for the urban heat island (UHI) that has developed over time. The project was designed as a preliminary study with a duration of one year. For this purpose, 17 JRBCs were obtained in Berlin, namely in Neukölln and in the Köpenicker Forest, representing eight tree species (European larch, Scots pine, Douglas fir, Copper beech, Common ash, Winter linden, English oak and Sessile oak) and subject to different influences of the UHI. In addition, five ARWCs from the Berlin area were compiled to three tree species (European beech, Scots pine and oak) from databases provided by GFZ Potsdam. First, the JRBCs were indexed by calculating quotients against the respective five-year weighted moving averages, emphasizing interannual fluctuations. The indexed JRBCs were correlated series for the previous and current year with monthly and seasonal averages from the Berlin-Dahlem weather station with respect to air temperature, precipitation and the de-Martonne dry index derived from these time. Highly significant negative correlations to June and summer temperatures were found, especially for the deciduous tree species. Compared to the precipitation and the dry index, positive and highly significant correlations in summer and June are also shown for the four hardwood species mentioned above. Furthermore, significant positive correlations of Scots pine to the temperature of February and March as well as winter and spring are remarkable. The findings on the hardwoods are interpreted as summer signals, those on the pines as winter signals. The Linden trees, on the other hand, which were also investigated, show this summer signal in only a clearly weakened and not significant form. Furthermore, it was possible to prove that the significant correlations with the summer dryness of oak and beech increase with the degree of urbanisation, here with the combination of sealed area and building proportion, and that this relationship is also highly significant in the statistical sense. This relationship becomes most obvious when considering the urban influence in a radius of 1000 to 2000 m around the location of the respective ARWC. Thus it could be shown that ARWC of urban trees are able to document urbanization and thus indirectly also the spatial and temporal development of the UHI. It is of particular interest that in the case of the relations to the June temperatures not only the overall spatial context between urbanization and tree reaction to climate signals is highly significant, but also all investigated site relations, i.e. the correlations between the June temperature and JRBC at all sites, exceed this significance level. Thus, a correlation has been found which allows the calculation of UHI intensities from annual rings via their correlation to June and summer temperatures with a high degree of statistical certainty. The hardwood species beech, ash, English oak and sessile oak turned out to be promising candidates for the calculation of summer UHI.
Publications
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(2017): Trees as Indicators of the Urban Heat Island (UHI). 36. Jahrestagung des AK Klima, 27.-29. Oktober 2017, Rauischholzhausen, Tagungsband S. 63
Schneider, S., S. Elsholz, B. Neuwirth, I. Heinrich, C. Schneider
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(2018): Bäume als Indikatoren von städtischen Wärmeinseln - Auswirkungen in Berlin. 8. REKLIM Regionalkonferenz, 25. September 2018, Potsdam
Heinrich, I., S. Schneider, S. Elsholz, D. Balanzategui, B. Neuwirth, C. Schneider
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(2018): Climate-Growth Relations of Trees affected by the Urban Heat Island in Berlin. TERENO International Conference 2018, 08.-12. Oktober 2018, Berlin
Schneider, S., S. Elsholz, B. Neuwirth, I. Heinrich, D. Balanzategui, C. Schneider
