Predicting hydrologic flows under climate change: The Tâmega Basin as an analog for the Mediterranean region

The potential effects of climate change on the hydrology of the Tâmega River basin, northern Portugal, are assessed by comparing simulated hydrologic scenarios derived from both observational climate databases for a recent past period (1950-2015) and EURO-CORDEX model simulations for the future (2021-2100). Future climate change scenarios are based on an ensemble of five climate model chain experiments and on two Representative Concentration Pathways (RCP4.5 and RCP8.5). Basin-mean annual temperatures are ca. 10% or 20% warmer than in recent past climate (12.4 °C) for RCP4.5 and RCP8.5, respectively. Furthermore, basin-mean annual precipitation decreases by approximately 8% or 13%, when compared to recent past (1255 mm). The Hydrological Simulation Program FORTRAN (HSPF) is applied to the historical data and to each of the five model simulations separately so as to simulate potential changes in flowrates. The model is calibrated and validated using 5 hydrometric stations, achieving satisfactory results regarding flowrate simulation. A reconstruction of flowrates within the entire river basin and over the historical period is accomplished, which is particularly useful when observed data is missing. The projected climate change impacts on annual flowrates reveal a decrease from 18% to 28% relative to observations (70.9 m³ s^-1). These findings provide valuable information for the future management and planning of water resources (water security) and can be largely generalized not only to other basins in Portugal, but also over most of Southern Europe and throughout the Mediterranean Basin, where significant warming and drying trends are widespread footprints of climate change.