The impact of climate change on the hydrological cycle and catchment processes has been extensively studied. In Wales, such changes are projected to have a substantial impact on hydrological regimes. However, the impact on the water abstraction capability of key sectors in the country, such as hydropower (HP) and public water supply (PWS), is not yet fully understood. We use the Soil and Water Assessment Tool (SWAT) to generate future (2021-2054) daily streamflows under a worst-case scenario of greenhouse gas emissions (Representative Concentration Pathway 8.5) at two large catchments in Wales, the Conwy and Tywi. SWAT streamflow output is used to estimate the abstractable water resources, and therefore changes in the average generation characteristics for 25 run-of-river HP schemes across Conwy and Tywi and the total unmet demand for a single large PWS abstraction in the Tywi. This unmet PWS demand is assessed using the Water Evaluation And Planning (WEAP) system under increasing, static, and declining demand scenarios. Mann-Kendall trend analysis is performed to detect and characterise the trends for both sectors.

Results show greater seasonality in abstraction potential through the study period, with an overall decrease in annual abstraction volume due to summer and autumn streamflow declines outweighing increases seen in winter and spring. For HP, these trends result in a projected decline in annual power generation potential, despite an increasing number of days per year that maximum permitted abstraction is reached. For PWS, under all future demand scenarios, annually there is an increase in the number of days where demand is not met as well as the total shortfall volume of water. Our results suggest that currently installed HP schemes may not make optimal use of future flows, and that the planning of future schemes should take account of these to ensure the most efficient operation is achieved. Moreover, PWS supply sustainability is under threat and will require management and mitigation measures to be implemented to ensure future supplies. Overall, our study provides a novel perspective on the future water resource availability in Wales, giving context to management planning to ensure future HP generation efficiency and PWS sustainability.