A Global Approach to Estimating the Benefit-Cost Ratio of Water Supply Measures in the Agricultural Sector

This study assesses at the global scale the potential costs and benefits of new infrastructure needed for the additional supply of irrigation water, focusing on rainwater harvesting, desalination and groundwater extraction. The cost and applicability of each measure is assessed and estimated separately. The potential benefit of additional water supply infrastructure is given by the water shadow price, which is generated by the global land and water use model MAgPIE (Model of Agricultural Productivity and its Impact on the Environment). Based on these results the irrigation potential (in Mha) is calculated. We find that groundwater extraction is cost-efficient in the most places and therefore has the highest irrigation potential (152.5 Mha) followed by rainwater harvesting (61.5 Mha) and desalination (0.5 Mha). The results reflect the current practice of supplying irrigation water, and a sensitivity analysis shows that rainwater harvesting has the largest potential to alleviate irrigation water scarcity through decreasing prices. The sensitivity analysis also shows that if the price of desalinated water continues to decline as it has in the past, desalination could become cost efficient especially in arid, coastal regions of the world.