Groundwater modelling for need assessment of command scale conjunctive water use for addressing the exacerbating irrigation cost inequities in LBDC irrigation system, Punjab, Pakistan

Bari Doab on Pakistan side of the border, about 29,000 km(2), is one of the most productive agricultural regions in the Sub-continent. The surge in population has increased the competition for available water resources. Ensuing to this, a number of irrigation-related issues have gained prominence. Effects of increasing climate aridity towards lower part of Bari Doab have emerged in the form of accelerated groundwater depletion. Lower Bari Doab Canal (LBDC) command, lying in the centre of Bari Doab, faces maximum spatial climate variability across its command area. This is the first model-based study of the long-term irrigation cost inequities due to successively increasing groundwater depletion towards the tail end. In the model, total water requirements of a grid cell are withdrawn from surface and/or sub-surface sources, based on rainfall and canal water availability. Groundwater pumping estimation is the most complex parameter; crop water deficit approach was adopted for the purpose. Due to excessive groundwater depletion, a tail-end farmer currently incurs 2.19 times higher irrigation costs as compared to the head-end counterpart. An additional depletion of 8-11 m is expected in the lower half of the command till 2031, in contrary to stable conditions in head end. As a result this irrigation cost anomaly is simulated to be further aggravating to 2.36 times in year 2031. Thus, irrigation systems with significant spatial climate variability need appropriate command scale conjunctive management of surface and groundwater by the concerned irrigation planning and management agencies. This would help in plummeting the exacerbating irrigation inequities by reducing waterlogging and groundwater depletion.