Assessing the ecosystem service flood protection of a riparian forest by applying a cascade approach

- Assessment of the ecosystem service flood protection of a riparian wetland.
- Workflow for a comprehensive and consistent implementation of the cascade approach.
- Use of EU flood hazard and risk maps, no site-specific hydrological modeling.
- Replacement costs 68 million EUR (1900 EUR/ha/yr) for an extreme flood.
- Avoided damage costs at least 4300 EUR/ha/yr for a 10-year flood.

We present a method for assessing the ecosystem service (ES) flood protection of riparian wetlands and apply it to a riparian forest in Germany. The suggested workflow implements a cascade approach to ES characterization in which current provisioning is assessed in four steps: (1) qualitative description of biophysical processes and structures, (2) definition and quantification of main and additional ecosystem functions, (3) qualitative description of economic and social benefits and (4) valuation. Future provisioning is addressed by identifying pressures and analyzing potential enhancements. Using flood hazard and risk maps produced in response to the EU floods directive, quantification of the ecosystem function water retention as well as monetary valuation by the replacement cost and avoided damage cost methods were achieved without site-specific hydrological-hydraulic modeling. Technical structures with the same water retention volume as the investigated ecosystem in case of an extreme flood would cost 68 million EUR (equivalent ES value EUR 1900/ha/yr). In case of a 10-year flood, the riparian forest avoids damage costs of at least 26 million EUR (EUR 4300/ha/yr). We provide suggestions for standardizing the application of both monetary valuation methods and discuss their information content as well approaches for non-monetary valuation of the ES flood protection.