Seasonal variations of vegetative indices and their correlation with evapotranspiration and soil water storage in a small agricultural catchment

A precise measurement of evapotranspiration (ET) and soil water storage (SWS) is necessary for crop management and understanding hydrological processes in agricultural catchments. In this study, we extracted the vegetative indices (VIs, including normalised difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), and enhanced vegetation index (EVI)) from satellite images of the Nučice catchment. We found a consistent seasonal pattern of VIs across the catchment with higher values and variation ranges during spring and summer and lower values and variation ranges during autumn and winter. Spatial variation of VIs also followed a seasonal trend, decreasing during crop growth and increasing after crop harvesting. Seasonal correlations were observed between monthly average ET and SWS with VIs throughout one crop season, which can be expressed mathematically as exponential functions. We propose that VIs can be used as a surrogate measure for ET and SWS in catchments with poor monitoring capabilities. Further studies are required to investigate the spatial distribution of ET and SWS throughout the watershed and their relationship with VIs. Furthermore, our research emphasises the importance of subsurface recharge in the water balance of the investigated fields. It suggests that subsurface flow may be influenced by potential gradients of the water table, driving its seasonal behaviour in response to bedrock morphology.