Global Environmental Change 17 (2007) 59–72 Assessing the robustness of adaptation decisions to climate change uncertainties: A case study on water resources management in the East of England Suraje Dessai a,b,à , Mike Hulme a,b a Tyndall Centre for Climate Change Research, UK b School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK Received 3 August 2006; received in revised form 20 November 2006; accepted 20 November 2006 Abstract Projections of future climate change are plagued with uncertainties, causing difficulties for planners taking decisions on adaptation measures. This paper presents an assessment framework that allows the identification of adaptation strategies that are robust (i.e. insensitive) to climate change uncertainties. The framework is applied to a case study of water resources management in the East of England, more specifically to the Anglian Water Services’ 25 year Water Resource Plan (WRP). The paper presents a local sensitivity analysis (a ‘one-at-a-time’ experiment) of the various elements of the modelling framework (e.g., emissions of greenhouse gases, climate sensitivity and global climate models) in order to determine whether or not a decision to adapt to climate change is sensitive to uncertainty in those elements. Water resources are found to be sensitive to uncertainties in regional climate response (from general circulation models and dynamical downscaling), in climate sensitivity and in climate impacts. Aerosol forcing and greenhouse gas emissions uncertainties are also important, whereas uncertainties from ocean mixing and the carbon cycle are not. Despite these large uncertainties, Anglian Water Services’ WRP remains robust to the climate change uncertainties sampled because of the adaptation options being considered (e.g. extension of water treatment works), because the climate model used for their planning (HadCM3) predicts drier conditions than other models, and because ‘one-at-a-time’ experiments do not sample the combination of different extremes in the uncertainty range of parameters. This research raises the question of how much certainty is required in climate change projections to justify investment in adaptation measures, and whether such certainty can be delivered. r 2006 Elsevier Ltd. All rights reserved. Keywords: Climate change; Adaptation; Uncertainty; Robustness; Sensitivity analysis; Water resources; East of England 1. Introduction Decisions about managing the environment are plagued with uncertainty. There is uncertainty about the past state of the environment, uncertainty about the current state of the environment and further uncertainty about the future state of the environment. It is therefore surprising that in the field of global environmental change little attention has been given to the sensitivity of management decisions to uncertainties in environmental predictions. There are some exceptions though. For example, Lempert et al. (2003, 2006) demonstrated the application of robust decision methods to the problem of global ARTICLE IN PRESS www.elsevier.com/locate/gloenvcha 0959-3780/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.gloenvcha.2006.11.005 Abbreviations: AWS, Anglian Water Services; EA, Environment Agency; ES&E, East Suffolk and Essex; GCM, General Circulation Model (or also Global Climate Model); GHG, Greenhouse gases; IPCC, Intergovernmental Panel on Climate Change; PDF, Probability distribu- tion function; MAGICC, Model for the Assessment of Greenhouse-gas Induced Climate Change; RCM, Regional Climate Model; SRES, Special Report on Emissions Scenarios; UKCIP, United Kingdom Climate Impacts Programme; UKWIR: United Kingdom Water Industry Re- search; WRP, Water Resource Plan; WRZ, Water Resource Zone; WTW, Water Treatment Works à Corresponding author. School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK. Tel.: +44 1603 591121; fax: +44 1603 590001. E-mail address: s.dessai@uea.ac.uk (S. Dessai).