Irrigation using slightly saline water from emerging desalination technologies as a solution to short-term drought

Societal Impact Statement: With global weather patterns becoming more extreme and unpredictable, sourcing reliable irrigation water is vital for improving food security and conserving drinking water in drought-prone areas. Emerging desalination technologies, which are still in the development phase, could potentially provide large quantities of slightly saline water for irrigation. However, we must first ensure that any benefits of alleviating drought using this water outweigh the negative impacts of salt stress. We examine the viability of such a system, using Tonga as a case study, with the aim of advocating for future use of emerging desalination technologies for irrigation in low- and middle-income countries. Summary: Emerging desalination technologies have the potential to be a cheap and energy-efficient source of irrigation water that could be used to alleviate short-term droughts in low- and middle-income countries. However, the water produced is unlikely to be completely salt-free, potentially increasing the risk of salt stress in crops. In this review, we give an overview of the various emerging desalination technologies. We then use Tonga as a case study for assessing the viability of temporarily irrigating crops with moderately saline water (≤100 mM salt) and assess whether the benefits of alleviating drought outweigh the negative impacts of salt stress. We conclude that, in Tonga, important food security crops are likely to have higher survival and growth rates if they are provided with moderately saline water during drought, including taro, pumpkin and yam. Water derived using the new technologies would not be prohibitively expensive to produce. Moreover, it would minimise the need to divert a diminishing supply of water away from drinking to irrigation. The continued improvement of emerging desalination technologies, together with field trials, will help to optimise the use of moderately saline water for irrigation. This is likely to be especially beneficial for achieving and maintaining food security in low- and middle-income countries in increasingly capricious conditions for agriculture.