The role of desalinisation to address aquifer overdraft in SE Spain

Aquifer overdraft is a major environmental and water management problem in Southeast Spain. In some areas, availability of desalinised seawater resources is being expanding, which provides an opportunity to address this problem at a lower social and economic cost. We analyse the economic impact of using several instruments to address the problem of non-renewable groundwater pumping in the aquifers of the Guadalentín basin: an environmental tax on groundwater use, the buyback of groundwater rights and the subsidization of desalinised resources. Their impact is assessed using a mathematical programming model that maximises the farm net margin resulting from the use of the available water resources for irrigation in the area. Our results show that, in the current situation of water availability, all the alternatives have significant economic impacts. Moreover, the first two alternatives would be unfeasible from a political point of view. The existence of abundant, though expensive, desalinised water resources in the foreseen future would reduce, but not eliminate, the negative economic impact of such instruments. Furthermore, water demand is so high in this area that even strongly subsidising desalinised water in exchange for reducing the use of groundwater would not allow to eliminate aquifer overdraft.