A framework to ensure scenario-neutral climate impact assessments better align with scenario-led projections

The uncertainty surrounding climate change presents a major challenge for the management of water resource systems, which are facing stresses to both supply and demand. To provide insight into how a system might perform under change, scenario-neutral climate impact assessments are being used increasingly to supplement ‘scenario-led’ climate projections. Scenario-neutral assessments stress-test a system against a range of potential climate changes, regardless of their plausibility, so that all major modes of system failure can be identified and characterised. However, when comparing the two approaches, results from scenario-neutral climate impact assessments often do not align with those from a scenario-led analysis. Regardless of the validity or otherwise of scenario-led projections, it is argued here that differences between the approaches arise because modes of change that are potentially critical for system performance were not considered in the scenario-neutral analysis. This potentially undermines the scenario-neutral approach, as the identification of system vulnerabilities is its key motivation. In an attempt to reconcile these two approaches, this research presents a framework and set of tools required to ensure a scenario-neutral analysis is stress-testing a system against the most critical modes of change. This includes casting a wide net on the potential modes of change considered, and the requirements of generating stochastic climate time series to do so. The Lake Como reservoir system is used as a case study, with results demonstrating the effects incorrectly framing a stress-test can have on decision making. We also demonstrate that only by correctly implementing all the key requirements of the scenario-neutral methodology will the method identify all primary system vulnerabilities.