Role of spatial resolution in simulating hydrological processes using a physically-based hydrological model

The hydrological responses of a catchment are predominantly governed by complex interactions among processes occurring at various spatial and temporal scales. Hydrological modelling serves as a powerful tool in assimilating this complex behaviour of hydrological systems. As hydrological processes exhibit non-linear behaviour at all scales, it becomes essential to understand how much spatial approximations are necessary for a model to adequately represent reality. This study aims at investigating the influence of spatial resolution of a physically-based hydrological model in capturing the hydrological processes of a catchment which is characterized by large scale variability in the regional distribution of water resources. In this study, the grid-based Variable Infiltration Capacity (VIC) model is employed at spatial resolutions of 0.125, 0.25, and 1-degree latitude by longitude over the Cauvery river basin in peninsular India. The model incorporates both surface and subsurface hydrological processes, features sub-grid land surface and vegetation heterogeneity, facilitates the inclusion of multiple soil layers with variable infiltration, and computes non-linear baseflow. The model is calibrated with respect to observed streamflow at various gauge stations located across the basin. The water balance components such as surface runoff, evapotranspiration, soil moisture at three distinct soil layers, and baseflow are estimated for the period 1951-2016. Performance evaluation of outputs obtained from model simulations adopting different spatial resolutions is carried out at seasonal and annual time scales. As the spatial scale increases, the catchment tends to organize and attenuate the complex behaviour of processes. This study provides significant insights towards adopting effective modelling strategies to ensure the adequate representation of hydrological processes in regionally complex catchments.