Spatial and temporal variations of, and the impact of climate change on, the dry season crop irrigation requirements in Bangladesh

Sustaining irrigation is vital for ensuring future food security in the face of population growth and a changing climate in Bangladesh. In this study, a daily soil water balance simulation model was used to estimate the net irrigation requirements of nine crops including Boro rice for the historical period of 1985-2010 and for future climate scenarios of 2030 and 2050 dry and average conditions using the A1B emission scenario. The average net irrigation requirement of Boro rice, the main crop, is 676 mm with temporally averaged spatial variation of 644-779 mm and spatially averaged temporal variation of 570-755 mm for base case planting on clay loam soil. The variations are due to the variation in crop evapotranspiration and rainfall during the cropping period. Changing planting or sowing date affects the net irrigation requirement which for Boro rice is lower in early (October-November) or late planting (January-February). The net irrigation requirement of Boro rice is about twice that required by wheat, maize, potato, tomato and sunflower, three times that of pulses and 5-6 times that required by oilseeds. The impact of climate change on irrigation requirements of Boro rice is small. The average irrigation requirement is projected to increase by a maximum of 3 % for the 2050 dry scenario. For other crops this is projected to increase by 1-5 % depending on the crop and the time of sowing/planting.