Impacts of Projected Climate Changes on Streamflow and Sediment Transport for Three Snowmelt-Dominated Rivers in the Interior Pacific Northwest

Abstract

Anthropogenic climate change is likely to have significant impacts on river systems, particularly on rivers dominated by seasonal snowmelt. In addition to altering the timing and magnitude of streamflow, climate change can affect the energy available to transport sediment, as well as the availability of sediment to be transported. These hydrologic changes are sensitive to local climate, which is largely controlled by topography, but climate models cannot resolve processes at these scales. Here, I investigate impacts of climate change on streamflow and suspended-sediment transport for three snowmelt-dominated rivers in the interior Pacific Northwest - the Tucannon River in Washington and the South Fork Coeur d'Alene and Red rivers in Idaho - using downscaled climate simulations from regional climate models (a range of three models plus an ensemble average) to drive a basin-scale hydrologic model. The results indicate that climate change is likely to amplify the annual cycle of river discharge, producing higher winter discharge (increases in ensemble mean January discharge ranging from 4.1% to 34.4% for the three rivers), an earlier spring snowmelt peak (by approximately one month), and lower summer discharge (decreases in ensemble mean July discharge ranging from 5.2% to 47.2%), relative to a late 20th-century baseline. The magnitude of the largest simulated flood under the ensemble-average climate change scenario increases by 0.6-41.6% across the three rivers. Simulated changes in suspended-sediment transport generally follow the changes in streamflow. These changes in discharge and sediment transport will likely produce significant impacts on the study rivers, including changes in flooding, physical habitat, and river morphology.