The Hydroclimate of the Ottawa River Basin Under Climate Change

The freshwater resource of the Ottawa River basin (ORB) is vital for ecological services and economic activities in the region. With climate change impacts becoming more evident, sustainable management is imperative. As a first step, it is important to assess impacts on hydro‐climatology. A coupled hydrological model (WATFLOOD‐RAVEN) was set up, calibrated, and validated, with all principal reservoirs implemented using the DZTR principle. The coupled model was forced with high‐resolution, bias‐corrected future climate projections. Ensemble results show a warmer and wetter future. Under RCP 4.5, which recent studies suggest as the more likely pathway, mean annual precipitation and temperature may increase as much as 8.6% and 3.2°C, respectively. Seasonal and monthly changes are more sporadic. Snowpack is expected to decrease substantially, while actual evapotranspiration increases moderately. Annual streamflow may rise by 7%–10%, but spring freshet streamflow is projected to shift earlier (1.1 days/decade) with a lower (12%) peak. Other indicators, such as time to center of mass and spring pulse onset, also point to earlier shifts. Results further indicate more frequent extreme high (Q10) and low (Q90) flow conditions. Substantial increases in winter reservoir inflows are likely to raise reservoir depths and reduce capacity to store the spring freshet. Better quantification of climate change impacts will aid in developing coordinated responses to climate‐related challenges.