Water resources managers are increasingly seeking information on the potential changes in hydrological regimes which may occur over the next few decades in order to plan adaptation measures. Uncertainty in projected changes to catchment-scale precipitation and temperature due to climate model uncertainty is well recognised, and addressed through the use of scenarios derived from several climate models or, indeed, many thousand scenarios in a probabilistic context (New et al., 2007). Uncertainty due to future emissions is often addressed through the use of ‘low’, ‘medium’ and ‘high’ emissions scenarios representing different assumptions about future economic and demographic change, but ‘low’ emissions scenarios still assume no explicit climate mitigation policy. A key question therefore is the extent to which climate mitigation policy either reduces impacts or buys time to allow adaptation.