Development and Evaluation of an Improved Process Based Paddy Irrigation Module for SWAT

Paddy cultivation consumes a large share of global irrigation water, yet conventional basin-scale hydrological models such as SWAT do not adequately represent paddy-specific hydrological processes. This study introduces a process-based paddy module, SWAT-PADDY, that integrates soil–water balance concepts from rice crop models (ORYZA and DSSAT-CERES Rice) into SWAT to simulate ponded-field hydrology under Alternate Wetting and Drying (AWD) and varying groundwater conditions. Performance was evaluated in ten paddy fields across two cropping seasons using observed field water levels and compared with ORYZA, DSSAT-CERES Rice, HYDRUS-1D, and the existing SWAT pothole approach. The puddling coefficient (PUD_COEFF) was the most sensitive parameter. SWAT-PADDY reproduced daily water levels with good accuracy (NSE > 0.40, R² > 0.50 in 7 of 10 fields), improved simulations of evapotranspiration and soil-water dynamics, and was consistent with HYDRUS-1D benchmark simulations. The enhanced framework extends SWAT’s applicability for basin-scale evaluation of irrigation management and sustainable rice production.