Both the number and the severity of rainfall events is expected to rise due to climate change (IPCC, 2014). Already now, citizens and their assets are affected by the impacts of heavy rainfall events to a significant extent (Davis and Naumann, 2017). In cities, the vulnerability toward extreme rainfall events is exacerbated by land cover changes and especially surface sealing (Gill et al., 2007).

Conventional engineering approaches have been found to be not sufficient, not cost-effective and not sustainable for urban stormwater management (Fritz, 2017). Therefore, the perspective shifted toward GI, i.e. multifunctional natural areas designed to deliver a wide range of ESS in order to complement, augment or replace built infrastructures (European Commission, 2013). Due to the characterization of GI and their ESS as public services, their value cannot be determined directly through market-based methods. Hence, their positive influence is often overlooked, undervalued or not detected by the current economic system and consequently not or not adequately recognized in decision-making, which is primarily based on CBA (European Commission, 2013; Kumar and Wood, 2010). This is also the case in Germany, where the IÖW develops a tool for cities to valuate the ESS of green areas in order to promote their acknowledgment by decision-makers.

Based on the theoretical background of valuation studies and the performativity argument, this work explored five applications of an extended CBA, which make the value of GI and their ESS ‘visible’. By comparing these approaches on the basis of different factors, their methodological and ideational similarities and differences became apparent and revealed how the benefits of ESS were rendered quantifiable. This information served as instructive set of recommendations for the IÖW-tool.

The findings show that the different authors use diverse methods to valuate ESS. These valuation methods express different interpretations of the authors about what counts in the valuation of ESS. The different interpretations became apparent in e.g. the level of detail of investigated ESS and are inevitably connected to a variety of factors, such as the understanding of CBA as a method, the quantification procedures and not least a set of necessary presumptions and estimates. Based on the findings, the IÖW-tool is recommended to integrate the ESS of water pollutant removal and maintain the possibility to quantify the value of those ESS, which are provided by the already existing green areas in a city. Further, the tool is urged to ensure transparency about the underlying procedures, which affect the valuation process and to accentuate the connection between the gain of monetary benefits and the related improvement of human well-being.