Increasing Evapotranspiration on Extensive Green Roofs by Changing Substrate Depths, Construction, and Additional Irrigation

Urban environments are characterized by dense development and paved ground with reduced evapotranspiration rates. These areas store sensible and latent heat, providing the base for typical urban heat island effects. Green roof installations are one possible strategy to reintroduce evaporative surfaces into cities. If green roofs are irrigated, they can contribute to urban water management and evapotranspiration can be enhanced. As part of two research projects, lysimeter measurements were used to determine the real evapotranspiration rates on the research roof of the University of Applied Sciences in Neubrandenburg, Germany. In this paper, we address the results from 2017, a humid and cool summer, and 2018, a century summer with the highest temperatures and dryness over a long period of time, measured in Northeast Germany. The lysimeter measurements varied between the normal green roof layer (variation of extensive green roof constructions) and a special construction with an extra retention layer and damming. The results show that the average daily evapotranspiration rates can be enhanced from 3 to 5 L/m2/day under optimized conditions. A second test on a real green roof with irrigation was used to explain the cooling effects of the surface above a cafe building in Berlin.

[1]  D. Pearlmutter,et al.  Urban Green Infrastructure as a tool for urban heat mitigation: Survey of research methodologies and findings across different climatic regions , 2018, Urban Climate.

[2]  Demin Zhou,et al.  Assessing the hydrological behaviour of large-scale potential green roofs retrofitting scenarios in Beijing , 2017, Urban Forestry & Urban Greening.

[3]  Rodrigo Picos,et al.  Thermal regulation capacity of a green roof system in the mediterranean region: The effects of vegetation and irrigation level , 2018 .

[4]  Reid R. Coffman,et al.  Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services , 2007 .

[5]  J. Lund.  Direct Heat Utilization of Geothermal Resources Worldwide 2005 , 2006 .

[6]  C.Y. Jim,et al.  Identifying keystone meteorological factors of green-roof stormwater retention to inform design and planning , 2015 .

[7]  Jianxun He,et al.  A Review of Green Roof Applications for Managing Urban Stormwater in Different Climatic Zones , 2018, Sustainability.

[8]  Stephan Weber,et al.  Modeling the reduction of urban excess heat by green roofs with respect to different irrigation scenarios , 2018 .

[9]  Pu Wang,et al.  A lysimeter study for the effects of different canopy sizes on evapotranspiration and crop coefficient of summer maize , 2018, Agricultural Water Management.

[10]  T. Muthanna,et al.  Green roof performance potential in cold and wet regions , 2017 .

[11]  Joshua B. Fisher,et al.  ET come home: potential evapotranspiration in geographical ecology , 2011 .

[12]  M. B. Jensen,et al.  Benefits of green roofs: A systematic review of the evidence for three ecosystem services , 2017 .

[13]  R. Deidda,et al.  Retention performance of green roofs in representative climates worldwide , 2017 .

[14]  T. Muthanna,et al.  Detention and Retention Behavior of Four Extensive Green Roofs in Three Nordic Climate Zones , 2018 .

[15]  J. Hewlett,et al.  A REVIEW OF CATCHMENT EXPERIMENTS TO DETERMINE THE EFFECT OF VEGETATION CHANGES ON WATER YIELD AND EVAPOTRANSPIRATION , 1982 .