Streamflow simulation in high topographic gradients and snowmelt-dominated watershed using the APEX model - Price River Watershed

Watersheds exhibiting high variability of elevation and temperature are common in western states of the U.S. Evaluating the performance of hydrological models under such extreme conditions is essential to improve hydrological and water quality predictions for reliable assessment of watershed management practices. The objective of this study was to assess the predictive capability of the Agricultural Policy/Environmental eXtender (APEX) model to simulate streamflow in the snowmelt-dominated watershed with a high spatial rainfall variability through 1) improving snowmelt processes and 2) allocating weather stations to sub-catchments based on elevation in the Price watershed, Utah. An initial evaluation of APEX performance indicated inability of the model to represent snowmelt processes and poor performance on streamflow prediction with the current Thiessen polygons approach for designating weather stations to sub-catchments. The result of the model simulation with an elevation-rainfall based approach combined with improved snowmelt routine showed a significant improvement in the model performance compared to the conventional APEX rainfall input designation. The enhanced APEX model provides major improvements in simulating hydrologic and water quality processes in the western rocky mountainous watersheds of the U.S, which will subsequently lead to better identifying best management practices for watershed managers.