A hydrologic and river ice modeling framework for assessing ungauged subbasin streamflow impact in a large cold-region river basin

ABSTRACT Modelling snow- and ice-affected streamflow in cold regions is challenging. Neglecting the streamflow from ungauged regions/sub-basins of a river basin in the inflow boundaries of a river ice model adds further uncertainties. This study combined a river ice model (River1D) with a hydrological model (Soil and Water Assessment Tool, SWAT) to investigate the impacts of ungauged sub-basin streamflow on peak flow simulation under both open water and river ice breakup conditions in the Peace River Basin (PRB). Results showed that ungauged sub-basins of the PRB can greatly affect peak flow simulation of the River1D for both open water and river ice breakup events, especially for flood events. Although they represent only about 26.54% of the whole modelled area in the PRB, the SWAT model simulated results show that the ungauged sub-basins can contribute nearly 50% of peak flow for the open water and river ice breakup flood events.