Revisiting the application of variable infiltration capacity (VIC) model in the Colorado River Basin using SMAP and GRACE

The Colorado River Basin (CRB) is a crucial water supply source experiencing prolonged drought conditions. Hydrologic models of the CRB have historically relied on streamflow calibration alone, limiting confidence in their representation of spatially distributed hydrologic processes. Here, we implemented a calibration and multi-source evaluation framework for the Variable Infiltration Capacity (VIC) model using observations from ground snow stations, streamflow records, and NASA’s Soil Moisture Active Passive (SMAP) and Gravity Recovery and Climate Experiment (GRACE) missions. After model calibration with snow and streamflow records, VIC achieved an excellent streamflow performance at key sub-basin outlets in the CRB (e.g., Nash-Sutcliffe Efficiency of 0.96 in the Upper Basin). Independent evaluations with SMAP further revealed a strong model performance in reproducing surface (R2 = 0.71) and root-zone (R2 = 0.81) soil moisture, with systematic elevation-dependent patterns in the comparison. A multi-year evaluation with GRACE demonstrated a robust reproduction of basin-scale terrestrial water storage dynamics and their interannual variability (R2= 0.66–0.86). This multi-source evaluation framework establishes the VIC model capacity to represent subsurface water storage dynamics in different land cover types, providing enhanced confidence for supporting water management in the CRB.