Neural Network Modelling of Climate Change and Reservoir Impacts on Upper Miño River Flow

Climate change is altering the global hydrological cycle and, when combined with human interventions such as reservoir operations, the river flow regime is further modified. Given the strong spatial heterogeneity of these impacts and the basin-specific nature of hydrological responses, regional studies are essential to assess local vulnerabilities. This study investigates projected changes in streamflow in the upper Miño River basin (northwestern Iberian Peninsula), including the impact of the Belesar reservoir, by comparing historical conditions (1985–2014) with future projections (2070–2099) under the SSP5-8.5 and SSP2-4.5 scenarios. Artificial neural networks were employed to model basin hydrology by estimating streamflow from temperature and precipitation data, and to simulate reservoir operations, achieving satisfactory validation performance.

Under the high-emission SSP5-8.5 scenario, results indicate a projected intensification of hydrological variability, with the 10th percentile, used to define low-flow conditions, decreasing by approximately 10%, whereas the percentile corresponding to a one-year return period (high-flow conditions) increases by about 5%, with the mean streamflow declining by more than 15%. Under the more moderate SSP2-4.5 scenario, changes are less pronounced, with a ~5% reduction in the low-flow percentile and a more moderate decrease in mean streamflow, while the high-flow percentile is expected to decrease by around 30 %, exhibiting an opposite trend to the extreme emission scenario. Reservoir operation was analysed under the SSP5-8.5 scenario to assess its regulatory capacity under future extreme conditions. Results show that reservoir management could mitigate projected impacts by redistributing water seasonally, more than doubling summer downstream flows compared to future natural conditions and reducing winter extremes, with peak flows lowered by approximately 15%. Overall, while future natural conditions are projected to become more critical, both moderate emission pathways and effective reservoir operation can substantially alleviate adverse hydrological impacts.