Component-wise Decomposition of Return Flow in Paddy Fields Based on DWAT Simulations

In paddy fields, both rainfall and irrigation water from reservoirs contribute interactively to the hydrological cycle. Quantitative decomposition of return flow based on its source is essential for efficient management of agricultural water. In this study, we employed the Dynamic Water Resources Assessment Tool (DWAT), a physically based semi-distributed model, to simulate major hydrological components in paddy fields including surface runoff, interflow, baseflow, infiltration, evapotranspiration, and water storage and separated them into rainfall and irrigation origin contributions.

The proposed component-wise decomposition framework enables spatio-temporal analysis of each hydrological process and uniquely allows monthly tracking of water storage by origin across soil and groundwater layers, providing a novel approach not explored in previous studies.

This framework can offer diagnostic insight into irrigation efficiency. For example, rapid conversion of irrigation water to surface runoff may indicate hydrological inefficiency, while effective utilization of rainfall implies potential for optimized supply operations. Such source-based decomposition provides a qualitative understanding of irrigation performance that cannot be inferred from return flow ratios alone.

This study can contribute to optimizing the operation of agricultural reservoirs and improving irrigation allocation policies, ultimately enhancing the sustainability of agricultural water use and supporting adaptive water resource management under increasing uncertainties driven by climate change.

This work was supported by Korea Environment Industry & Technology Institute(KEITI) through Aquatic Ecosystem Conservation Research Program, funded by Korea Ministry of Climate, Energy and Environment(MCEE). (RS-2025-02304832)