Changes in water requirements of dry season rice under climate change : quantifying recent & future changes and developing adaptation strategies in Northwest Bangladesh

Abstract

This study focuses on quantifying the changes in water requirements of dry season Boro rice under recent and future climate changes. It also assessed the effectiveness of shifting trans-/planting date of Boro rice to adapt to climate change and prioritized adaptation options in Northwest Bangladesh. The FAO developed CropWat 8.0 model was used to quantify changes in water requirements for recent decades (1980 - 2013) and future moderate (RCP 4.5) and rapid (RCP 8.5) climate scenarios in 2050s and 2080s time periods. The growing degree-days method was used to quantify changes in growth duration of rice as affected by climate change. Future water requirements of Boro rice for early, normal and late planting and possibilities of high-temperature stress during critical periods were assessed. Furthermore, the study identified and ranked adaptation options based on local experts’/stakeholders’ opinion for better agricultural water management to cope with climate change. Both the analysis of recent trends and of future changes in water requirements yielded robust signals of a possible decrease in water requirements of dry season Boro rice. Declining recent trends of water requirements were found with reduction of reference crop evapotranspiration. In future, the estimated net irrigation requirement of Boro rice showed a reduction, despite some increase in daily reference crop evapotranspiration due to shortened Boro growing season. The net irrigation requirement of Boro rice has decreased by 11% during the last three decades at an average rate of 4.4 mm year-1, despite a slight decrease in effective rainfall, mainly because of high rate of decrease of potential crop evapotranspiration (5.9 mm/year). The net irrigation requirement of Boro rice will decrease by 1.6% in 2050s and 7.4% in 2080s for RCP 8.5 scenarios averaged over all models and districts. This study also found that late planting can substantially reduce irrigation demand, but the option is very limited due to both day- and night-time heat stress. Early planting accounts for high water demand but ensures suitable temperatures during the critical growth stages of the crop. Transboundary co-operation, integrated water resources management and adjustment of irrigation methods are the top three adaptation measures, as ranked by stakeholders. Integrated, co-operative and advanced technological strategies are preferred by local stakeholders over simple in-field measures to cope with climate change. This study has improved existing knowledge on changes in water requirements of dry season rice due to changes in climatic parameters. These insights are useful to understand the possible changes in regional agricultural water demand, especially for rice dominated areas. Furthermore, the study has broaden our knowledge about the effectiveness of changing trans-/planting date of dry season rice to adjust to climate change and the local stakeholders’ preferences of adaptation measures. This helps to make informed decisions for future adaptation planning to cope with climate change.