The science and politics of climate risk assessment in Australia's Murray Darling Basin.

• Climate adaptation policy in a large river basin is explored. • Empirical study of science and policy interactions during actual reforms. • Interviews with senior research policy professionals reveal dynamics of policy formulation. • Proposes legally prescribed procedures for utilising science in environmental policy formulation. Climate change has many disruptive consequences, particularly in large river basins experiencing drying trends and declining water availability. With pressure for more adaptive policies, understanding how institutions governing water are adapting to climate risks has broad international relevance. This paper examines the challenges of climate risk assessments in Australia's Murray Darling Basin, an economically and culturally important basin where national legislation mandates a Basin Plan based on the best available science. However, despite repeated scientific warnings about a drying climate, the current Basin Plan does not reduce estimates of water resources available, and its climate risk management relies on a bricolage of policy mechanisms, which appear insufficient for the magnitude of predicted changes. This paper outlines the findings of original research exploring why this occurred. It draws on interviews with 30 senior public policy professionals and researchers with deep experience in climate and water policy. The interview data indicate that minimising political risks were the principal reasons for abandoning proposed reductions in entitlements and for relying on historical averages for estimating water availability. As the reform process evolved, decisions about water-planning techniques became increasingly politicised, and the adoption of explicit climate adaptation measures became problematic. As a result, the Basin Plan neither reflects the broad scientific consensus about climate change nor makes specific allowances for declining water availability. Climate risks are downplayed while concerns about levels of scientific uncertainties appear overstated. Importantly, lessons emerge from this examination that could contribute to the revisions of the Plan, scheduled for 2026. More generally, the research finds that proactive climate adaptation policies for large river basins require sustained and well-designed institutional reforms, particularly the adoption of legally prescribed procedures for utilising science - and accounting for its use - in controversial environmental reforms. [ABSTRACT FROM AUTHOR]