Assessing the influence of climate change on irrigation water requirements for Boro rice in a subtropical region

Climate change increasingly disrupts agricultural water use and food security, particularly in subtropical regions such as Bangladesh. As a water-intensive crop grown during the dry winter season, Boro rice is highly sensitive to climatic variability. This study examines how changing climatic conditions influence irrigation water requirements (IWR) for Boro rice across three drought-prone districts in northwestern Bangladesh. Using daily weather data from 1980 to 2020 and the FAO CropWat 8.0 model, we estimated reference evapotranspiration (ETref), potential evapotranspiration (ETp), effective rainfall (ERF), and gross irrigation water requirement (GIWR). Long-term trends were analyzed using the Mann–Kendall, Sen's slope, and Pettitt tests. Results revealed significant declines in ETref and ETp, mainly due to reduced sunshine duration, lower wind speeds, and higher relative humidity. The average decline rate of ETp was 2.77 mm year−1, while GIWR decreased by 1.98 mm year−1. Among the study areas, Joypurhat showed the largest GIWR reduction (–5.77%), whereas Bogura showed a slight increase (0.02%), reflecting localized climatic and soil variations. Socioeconomic factors such as groundwater depletion, high energy costs, and limited irrigation access further constrain water use. The findings highlight the need for climate-smart irrigation strategies to improve water efficiency and agricultural resilience under changing climatic conditions.