AquaCrop–DNDC Modeling of Rice Yield and Greenhouse Gas Emissions Under Alternate Wetting–Drying and Climate Change in Coastal Peru

Paddy rice on the arid Peruvian coast is water- and emission-intensive; alternate wetting and drying (AWD) lowers both, yet their joint response under climate change is rarely quantified. AquaCrop-OSPy and DNDC were coupled one-way under a single bias-corrected forcing, each calibrated on its own 2023 observable, for Oryza sativa cv. INIA 515 Capoteña, and projected to 2100 under three CMIP6 scenarios. Canopy cover was reproduced within 0.3 to 1.7 percentage points in-sample and 1.8 to 5.2 out-of-sample, although the grain yield was underestimated by 24 and 39%. AWD20 saved 27.5% of the irrigation water for 7.9% less grain (+27% water productivity) and cut the global warming potential by 76% as measured in 2023 and by 86–89% as simulated, representing a model ceiling. Carbon fertilization sustained the yield to 2100 in every scenario; the late-century downturn under SSP5-8.5 proved specific to the CO2 formulation of the crop model, and flowering sterility was never reached. Adaptive irrigation changed nothing, but pairing AWD20 with a rescheduled planting window increased the yield by 14% and preserved 86% of the mitigation. Emission projections remain conditional on the crop carbon input, which the one-way coupling transfers only as a seasonal total.