Assessing climate change impacts on stream temperature in the Athabasca River Basin using SWAT equilibrium temperature model and its potential impacts on stream ecosystem.

Stream temperatures, which influence dynamics and distributions of the aquatic species and kinetics of biochemical reactions, are expected to be altered by the climate change. Therefore, predicting the impacts of climate change on stream temperature is helpful for integrated water resources management. In this study, our previously developed Soil and Water Assessment Tool (SWAT) equilibrium temperature model, which considers both the impacts of meteorological condition and hydrological processes, was used to assess the climate change impact on the stream temperature regimes in the Athabasca River Basin (ARB), a cold climate region watershed of western Canada. The streamflow and stream temperatures were calibrated and validated first in the baseline period, using multi-site observed data in the ARB. Then, climate change impact assessments were conducted based on three climate models under the Representative Concentration Pathways 4.6 and 8.5 scenarios. Results showed that warmer and wetter future condition would prevail in the ARB. As a result, streamflow in the basin would increase despite the projected increases in evapotranspiration due to warmer condition. On the basin scale, annual stream temperatures are expected to increase by 0.8 to 1.1 °C in mid-century and by 1.6 to 3.1 °C in late century. Moreover, the stream temperature changes showed a marked temporal pattern with the highest increases (2.0 to 7.4 °C) in summer. The increasing stream temperatures would affect water quality dynamics in the ARB by decreasing dissolved oxygen concentrations and increasing biochemical reaction rates in the streams. Such spatial-temporal changes in stream temperature regimes in future period would also affect aquatic species, thus require appropriate management measures to attenuate the impacts.