The hidden regional costs of improving irrigation efficiency: a case study from India

Indian agriculture depends heavily on groundwater pumping. These water withdrawals are not all consumed directly by the crops they irrigate; estimated irrigation inefficiencies indicate that two thirds of irrigation water withdrawals in India are “lost”. Withdrawals lost through leaky canals and flood irrigation systems become runoff and re-enter the surface water system. This mechanism causes irrigation inefficiencies to re-distribute water across basins, and can significantly alter the amount of surface water available both locally and downstream. In this study we used a gridded water balance model to track the path of groundwater from its pumping location, through irrigation systems, and to its downstream consumption or discharge from river mouths. We find that nearly half of all groundwater pumped at rates higher than recharge are re-used downstream. Furthermore, increasing the efficiency of irrigation systems has the potential to decrease surface water levels downstream. We used the water balance model to simulate scenarios of increased irrigation efficiency and find that doubling efficiency does not reduce India\u27s dependence on pumping deep groundwater by half as would be expected from standard measures of irrigation efficiency, but rather by only 38%. Increasing irrigation efficiency to 100% (i.e., no irrigation water losses) causes a decrease in modeled river discharge in both the Indus and the Ganges. The water balance model can also simulate scenarios in which groundwater pumping is limited to recharge rates. In this case, increasing irrigation efficiency to 100% results in a decrease in available surface water across large regions of eastern India, revealing the region\u27s dependence on surface water that was originally sourced from deep groundwater pumping upstream. These results have two important implications. First, they raise questions about the strategy of increasing irrigation efficiency as a strategy for reducing water stress. Second, they show that a larger portion of Indian agriculture is dependent upon groundwater pumping than just the regions that are engaging in pumping