Future changes in water requirements of Boro rice in the face of climate change in North-West Bangladesh

Abstract

Understanding future changes in crop water requirements and irrigation demand in the context of climate change is essential for long-term water resources management and agricultural planning. This study investigates the impacts of climate change on future water requirements of dry season Boro rice. Climate scenarios for four North-West districts of Bangladesh were constructed from the outputs of five global circulation models using a combination of statistical downscaling and bias correction. The generated climate data were used as input for CropWat to estimate water requirements of Boro rice for 2050s and 2080s (using 30year average climate data). Reference crop evapotranspiration (daily ETo) is increasing in the future, mainly due to higher temperatures. Potential crop water requirement (∑ETC) of Boro rice, however, will reduce by 6.5% and 10.9% for RCP 4.5 and 8.5, respectively for 2050s; and by 8.3% and 17.6% for RCP 4.5 and 8.5, respectively for 2080s compared to the reference period (1980–2013). ΣETC will decrease because of a lower number of growing days due to the phenological response of rice to higher temperatures. Low rainfall accessibility under a shortened Boro season leads to an increase in the amount of irrigation water required to satisfy crop evapotranspiration demand. Although daily water requirements will increase, the total net irrigation requirement of Boro rice will decrease by 1.6% in 2050s and 7.4% in 2080s for RCP 8.5 scenario on average for all models and districts. Estimated net irrigation requirements showed high variations for different climate models, mainly due to a high variation in the projected rainfall. For improved water management planning, close monitoring and periodic evaluations are necessary to understand future directions of change in rainfall amounts and distribution.