Uncertainties in projected future flood risk and challenges of detecting signals of change from observations highlight the need to advance process understanding through linking hydrological extremes to large-scale climate drivers. In Ireland, recent years have highlighted vulnerability to flooding yet little research has been undertaken exploring hydroclimatic signatures of change in extremes at different scales, in part due to a lack of quality assured data for relevant variables. This is an important research gap given Ireland’s sentinel position on the Atlantic margin of northwest Europe and is addressed within this thesis. The Island of Ireland (IoI) is classified into 3 Extreme Rainfall Regions (ERRs) reflecting distinct extreme precipitation climatologies, thus furthering understanding of physical flood-producing mechanisms. A comprehensive statistical trend analysis is performed on extreme precipitation and flood indices under a standard statistical framework. Results show a robust increasing trend in extreme precipitation magnitude, frequency, duration, and intensity. Similar results are found for flood indices at longer time-scales but limited station density prohibits stronger conclusions. Atmospheric drivers of flood occurrence are reconstructed back to 1872 using an objective weather classification scheme and used to identify four flood rich periods: 1.) 1870s to 1890s; 2.) late-1900s to mid-1930s, 3.) a short spell in the 1980s, and 4.) late-1990s onwards. The recent flood rich period is not unprecedented at the centennial time-scale. Moving towards attribution, the North Atlantic Oscillation (NAO) is found to modulate flood propensity, with strongest influence in the west and northwest. At the catchment scale the utility of an attribution framework based on the method of multiple working hypotheses is posited using the Boyne catchment as an exemplar. Results show the complexity of attributing hydroclimatic change at the catchment scale where the system is influenced by internal and external change. This work advances understanding of hydroclimatic flood processes and establishes new datasets that together will be important for better managing current and future flood risk and opens prospects for new management tools in Ireland, especially seasonal hydrological forecasting.