Evaluation of green roof hydrologic performance for rainwater runoff management in Hamburg

Abstract

Adaptation to the unpreventable consequences of climate change is one of the main challenges for cities in the coming decades. Especially for urban areas, where consequences of climate change will occur concentrated, there is a need for sustainable climate change adaptation measures. Our research focusses on one example of adaptation measures: green roofs. In addition to long-term economic benefits, they offer a wide range of benefits for urban ecosystems. Besides thermal benefits, like reduction of heating and cooling costs and reduction of the urban heat island effect, green roofs improve the urban water cycle, reduce air pollution, and enhance biodiversity. In Hamburg, heavy precipitation events regularly lead to overwhelmed urban drainage systems. Such events are expected to occur more often in the future with increasingly frequent (and intense) extreme precipitation events. Therefore, rainfall-runoff measurements of an extensive green roof on the HafenCity University building are carried out to determine the water retention capacity of the roof and to estimate the potential retention during heavy precipitation events. The long-term results show rainfall-runoff relationships under various weather conditions and are important for the development of future water management strategies and to overcome doubts about the effectiveness of green roof water retention, especially related to extreme precipitation events.