Abstract
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 café building in Berlin.
Highlights
Water evaporation is the largest hydrological process on earth and involves energy transformation.Precipitation depends on the evaporation characteristics
Urban environments are characterized by dense development and paved ground with reduced evapotranspiration rates
The lysimeter measurements varied between the normal green roof layer and a special construction with an extra retention layer and damming
Summary
Water evaporation is the largest hydrological process on earth and involves energy transformation. The combination of evaporation and transpiration is evapotranspiration (ET). A reduction in the actual evapotranspiration (ETa ) enhances the conversion of short-wave into long-wave global solar radiation and sensible heat. The decreasing global evaporation rates are directly related to the ongoing reduction of forest land and urbanization, resulting in higher surface temperatures and amplified urban heat island (UHI) effects [1]. Decentralized rainwater management is focused on ET instead of draining rainwater or allowing it to seep away
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