Assessment of responsiveness of water balance components to soil parameters characterized in variable infiltration capacity model

Abstract

This study evaluates the sensitivity of soil parameters used for soil stratification in the variable infiltration capacity (VIC) hydrological model and their influence on water balance components under contrasting hydro-climatic conditions. The selected parameters include b-infilt, which defines the shape of the infiltration curve; Ds, the fraction of maximum baseflow velocity; and Ws, the fraction of maximum soil moisture at which non-linear baseflow begins. The Malaprabha catchment was selected as the study area, considering a rainfall deficit year (2001) and a rainfall surplus year (2005). Three representative land cover–soil combinations were analyzed: clayey soil with forest cover, clayey soil with agricultural cover, and loamy soil with agricultural cover. Sensitivity analysis was performed using the Relative Sensitivity Index (RSI). Results show that runoff and evapotranspiration are highly responsive to b-infilt (RSI: 0.01–0.79), while Ds strongly influences baseflow (RSI: 0.08–0.93). In contrast, Ws affects both runoff and baseflow, exhibiting a direct relationship with runoff and an inverse relationship with baseflow (RSI: 0–1). The study reveals greater parameter sensitivity under unsaturated soil conditions and provides new insights into the differential response of VIC soil parameters across rainfall regimes and land cover–soil combinations, supporting improved model calibration and hydrological simulations.