DDD Conference

Dr. Mohammad Rahman

Urban Greenspaces to Cool Our Hot Cities in Relation to Soil Moisture and Species Traits

Technical University of Munich, Germany

Urban green infrastructure is widely known for promoting adaptive capacities of cities to climate change by alleviating urban heat island. However, a detailed understanding on the mechanisms of the various components of greenspaces in different local climates on reducing heat loads at local and city scale is still limited. We investigated surface energy balance, boundary layer air-cooling through evapotranspiration over the last four years across two major cities in Germany – Munich and Würzburg. Firstly, we found that the differences between sun and shade were steeper over the grass surfaces and during the wet spells (evapotranspiration rate > 1.5 L m-2 d-1). In contrast, sensible heat fluxes between grass and paved surfaces were not different during the dry spells. On a separate study in Würzburg, we found that mean air temperature (AT) of inner city sites were higher by 1.3 °C during summer compared to sub-urban sites. Regarding species traits, we compared two ecologically contrasting species – Tilia cordata and Robinia pseudoacacia. T. cordata with 35% higher leaf area index and diffuse porous wood anatomy provided four times more transpiration thus, up to 2.8 °C AT reduction (ΔAT) and up to 2.6 g m − 3 (ΔAH) increase in absolute humidity compared to 1.9 °C of ΔAT and 1.9 g m − 3 of ΔAH within the tree canopies of R. pseudoacacia. Our results underline the importance of both shade and grass surfaces in reducing the urban heat loads, in particular, the added benefits of tree shade with higher atmospheric demand.

 

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