Estimation of Groundwater Evapotranspiration and Extinction Depth Using Diurnal Water Table Fluctuation and Remote Sensing Observations: A Case Study in Agriculture-Dominated Watershed of Eastern India

Abstract

Groundwater models meticulously considering the water balance components have paramount importance in sustainable decision-making on groundwater. Plant uptakes and transpires water from the groundwater, called groundwater evapotranspiration (ETG), ?is one of the major contributions to the water balance. ETG needs to be quantified for shallow groundwater areas as they account for major depletion in groundwater. This study evaluated the White and modified White methods to estimate ETG for the agricultural-dominated Rana watershed with a tropical savanna climate in Eastern India. This modified method uses the sine function to capture the diurnal fluctuation of groundwater and estimates daily to seasonal ETG. Additionally, a physical-based modeling strategy was adopted to estimate the ETG over the study basin as a function of soil moisture change from the surface to the saturation depth and delineate the extinction depth of ETG. Additionally, this study compared the efficacy of both the empirical methods with the physical-based model to estimate ETG in agricultural land use. Results showed that ETG was nearly 50�70% of crop evapotranspiration and was higher in magnitude in the dry periods of the year due to less availability of topsoil moisture. The range of extinction depth was observed to be from 1 to 3 m for the hard rock area, whereas the same was from 5 to 9 m for other regions. When the comparison is made on a seven-day window, the modified White method produced an R 2 of 0.88, whereas that of the White method was 0.40. Conclusively, the modified White method reliably estimates the ETG and can be applied successfully in shallow groundwater level regions for reducing uncertainty in groundwater head prediction due to oversimplification of water balance components. � 2024, The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd.