Future-proofing raised bed irrigation for rabi maize using sensor-based soil moisture monitoring, AquaCrop modeling, and CMIP6-based climate projections in Bangladesh

Rabi maize production in north-central Bangladesh depends entirely on groundwater irrigation during a climatically water-stressed period, and progressive aquifer depletion with CMIP6-projected warming poses an escalating threat to its long-term viability. This study presents the first integration of multi-season field experimentation, twice-daily sensor-based soil moisture monitoring (HH2 Moisture Profiler, Delta-T Devices), FAO AquaCrop calibration and validation, and a ten-model CMIP6 ensemble to evaluate raised bed furrow irrigation as a climate adaptation strategy in Mymensingh. Four configurations, conventional flood (CF), narrow (NRB, 25 cm), medium (MRB, 65 cm), and wide (WRB, 110 cm) raised beds, were tested across two seasons (2023–24, 2024–25) under a randomized complete block design. The AquaCrop model achieved R² = 0.997 and NSE = 0.813 for grain yield (GY) at calibration, with near-identical validation performance (R² = 0.997; NSE = 0.829) and PBIAS within ±5.1%. MRB delivered the highest GY (12.65 and 12.56 t/ha), water productivity (4.10 kg/m³), and harvest index (0.48), reducing seasonal water use by 19.1% and 21.4% relative to CF. Sensor profiles confirmed MRB sustained root-zone moisture at 200–400 mm depths comparable to CF despite lower water inputs. Bias-corrected CMIP6 projections, evaluated across the ten-member ensemble and four SSP scenarios, indicated MRB yield losses of 0.71% under near-term SSP1–2.6 (ensemble coefficient of variation, CV = 3.2%, high confidence) to 14.83% under far-term SSP5–8.5 (CV = 16.4%, wider uncertainty); MRB nonetheless retained the highest simulated GY (11.56 t/ha), exceeding WRB (8.86 t/ha) and NRB (10.15 t/ha) under the most severe trajectory, with this relative treatment ranking preserved across the full ensemble uncertainty envelope. These findings establish the 65 cm raised bed as the primary climate-smart adaptation pathway for sustainable rabi maize production in Bangladesh, with high confidence for the near- and mid-term horizon and directional, though less precise, support for the far term.