Modeling Boro rice water requirements and irrigation schedules in Mymensingh, Bangladesh, under subtropical climate change

• Projected temperature increases and rainfall reductions during the Boro growing season in Mymensingh, Bangladesh. • Crop water requirements could increase by up to 15.12% by the 2070s under the RCP 8.5 scenario. • Irrigation demands may rise by 29.90% in the 2070s, putting pressure on natural water supply. • Changes in irrigation frequency, with up to 16 irrigation events needed in future scenarios compared to 12 in the baseline period. • Adapting farming and irrigation practices is essential for ensuring food security amid climate change. Boro rice cultivation, crucial for Bangladesh's food security, relies heavily on irrigation during the dry season. This study evaluates crop water requirements (CWR) and irrigation schedules for Boro rice in Mymensingh, Bangladesh, under projected climate scenarios in a humid subtropical environment. Historical climate data (2000–2023) and three global circulation models (BCC-CSM1-1-M, HadGEM2-ES, and MIROC5) were used to project changes under representative concentration pathways RCP 4.5 and RCP 8.5 for the 2040s and 2070s. Results indicate significant temperature increases, with average minimum temperatures rising by 0.30-1.87°C (RCP 4.5) and 0.35-1.89°C (RCP 8.5) in the 2040s, further intensifying to 1.63-2.56°C by the 2070s. Maximum temperatures show more dramatic increases, reaching up to 4.46°C (RCP 4.5) and 7.57°C (RCP 8.5) by the 2070s. Precipitation projections reveal concerning trends, with January rainfall decreasing by up to 53.20% under RCP 4.5 by the 2040s. These climatic shifts are expected to drive up irrigation demand (i.e., CWR) by 20.20% (RCP 4.5) and 21.31% (RCP 8.5) in the 2040s, potentially reaching 29.90% by the 2070s under RCP 8.5. Additionally, the study identifies a need for more frequent irrigation events, emphasizing timely adjustments in irrigation management. While the study assumes constant humidity, which may affect projection accuracy, it provides crucial insights for policymakers, farmers, and water managers. The findings emphasize the urgent need for adaptive water management strategies and improved irrigation practices to sustain Boro rice production under changing climate conditions. This research serves as a valuable resource for developing climate-resilient agricultural policies and water management solutions.