Testing Meta-Regression Analysis in the context of NBS restoration measures: The case of Brague River

Abstract

Co-benefits frequently carry most of the economic value that a Nature Based Solution generates, but they are also the hardest part of the appraisal to price. Local willingness-to-pay studies are expensive and cannot be run for every candidate project. Value transfer — taking values estimated elsewhere and adjusting them to the site in question — is the usual practical answer, and its credibility depends entirely on whether the adjustment is defensible.

This study tests meta-regression analysis as the transfer mechanism in the La Brague basin, where a local contingent valuation exercise was carried out with more than 400 respondents alongside the NAIAD assessment. The meta-regression is built from the published valuation literature and used to predict the site's co-benefit values; the predictions are then compared against the locally elicited ones. Presenting both numbers side by side is the point of the exercise: it shows how much confidence a transferred value deserves, and therefore how large a margin should be attached to a cost-benefit result that depends on it.

The result matters for the wider NAIAD finding that NBS strategies in the basin only balance their costs once co-benefits are counted.