Anticipatory adaptation to climate change in the water resources sector is essential to reduce or avoid expected impacts on water resources availability and management. Anticipating how water systems are likely to respond to a changing climate is a challenging task, due to the difficulties in detecting clear signals of anthropogenic climate change from hydrological observations, along with uncertainties in future climate change impacts. To date in Ireland, studies with regard to climate change have focused on the traditional top-down, climate-scenario-driven impact assessments. Little research has gone beyond this traditional approach and examined how uncertain information on the future resource availability and on the vulnerability of water supply systems to climate change, can be incorporated into decision-making. In addressing these challenges this thesis first examines observations of river flows from a network of near-natural catchments for evidence of climate-driven trends. Selected flow indicators relevant to water resource management are extracted and analysed for climate-driven trends, using different approaches including fixed periods of record and moving windows tests, to explore the nature of change in observations. Results indicate that the derived time series of median and low flow indicators in Ireland are dominated by natural variability, which makes the detection of a climate change signals in river flows rather difficult. The trends obtained for observed summer flows indicate a disagreement with established Irish climate change projections of drier summers and more extreme drought conditions. Given the shortage of coherent trends, the magnitude and amount of time required for change to be detected suggest that change signals will not be detected, using conservative significance levels, in the time frame required for adaptation. Therefore, anticipatory adaptation in the water resources sector cannot only rely on observed flow information but also needs to be based on the assessment of vulnerabilities to projected future changes. In developing a tool to support water resources decision-making in Ireland, a physically based hydrological model (HYSIM) is coupled with a water resources model (WEAP) and applied to 12 different case study surface water abstraction points in Ireland to explore the effectiveness of selected adaptation options. The tool incorporates uncertainties in Irish future climate scenarios and hydrological model application. To facilitate application to un-gauged river reaches, from which water is abstracted, the tool incorporates a proxy-basin method, incorporating hydrological model uncertainty to obtain feasible ranges of future hydrological conditions. Non-climatic pressures such as population growth projections are also included in the modelling framework. Threshold-based indicators are employed to assess the water resources system performance for selected robust adaptation options of demand and leakage reductions. Results indicate that the sensitivity of individual water resource systems to future changes and adaptation decisions is context specific. This is due to the particular hydrological and water supply system characteristics and requires case-by-case analysis. For a number of abstraction points examined in the east of the country, the tested scenarios are not sufficient to reduce vulnerability for a considerable proportion of the uncertainty space considered. Additional or different adaptation options will be required in these situations to increase system performance. The development and application of this tool marks a first attempt at using climate scenarios and their associated uncertainties for decision appraisal and marks a first step in this direction in Ireland, thereby providing a bridge in transitioning to a fuller methodology for decision appraisal. In developing a future research agenda priorities are distilled.