The impact of rainfall distribution methods on streamflow throughout multiple elevations in the Rocky Mountains using the APEX model—Price River watershed, Utah

The hydrology of mountainous watersheds in the western United States is significantly influenced by snow year‐round. It is widely known that topography affects precipitation; however, the knowledge of how watershed rainfall designation methods affect streamflow is not well understood for high‐relief areas. The objectives of this study were to assess the predictive capability of the Agricultural Policy/Environmental eXtender (APEX) model to simulate streamflow in a snowmelt‐dominated watershed with high spatial rainfall variability through (a) allocating weather stations to sub‐basins based on a conventional Thiessen polygon method (CM) or a rainfall‐elevation–based input (RE) and using an areal average Parameter‐Elevation Regression on Independent Slopes Model (PRISM) rainfall designation and (b) improving the snowmelt processes in the Price River watershed, Utah. The updated APEX model with snowmelt parameters significantly improved spring flood simulation. The RE was the most robust method in snowmelt and seasonal streamflow simulations compared with the CM and PRISM rainfall designations. Adapting the APEX model to simulate snow‐dominant complex terrains will provide crucial water quantity and quality predictions for reliable environmental and watershed management assessment. Core Ideas Rainfall designation methods were evaluated for streamflow simulation in a mountain watershed. Snowmelt simulation in APEX was revised to adjust the timing of snowmelt. APEX performed better with the elevation‐based rainfall designation method than other methods.