From global to local scale: How international experiences contribute to the fossil water management of the Guarani Aquifer System

Abstract

The Guarani Aquifer System (GAS) helps to guarantee water security for over 100 cities in Argentina, Brazil, Paraguay, and Uruguay, where more than 15 million people live. Total extraction can exceed 1.04 km³.yr−1. Withdrawals in 80% of its area are considered non-sustainable, as its waters reached the aquifer more than 30,000 years ago. Using non-renewable water can be justified when socio-economic benefits outweigh the negative impacts and must be carefully managed. This article consolidated subsidies for better management and governance of fossil aquifers, highly representative in global groundwater, focusing on three critical issues: (i) the relevance of monitoring and assessing the use of fossil waters, (ii) the rising extraction costs due to aquifer depletion, and (iii) solutions that integrate hydrogeological, socio-economic, and environmental components, based on studies in arid and semi-arid regions where “non-aquifer” options are limited. We found that proper management is based on mapping the critical depletion areas, with a higher well density or greater extraction, and establishing the control of groundwater usage in these locations. This management is based on an adaptive strategy through continuous data collection, guiding management in a virtuous cycle. The study also underscores the role of stakeholders in groundwater governance and solutions like Managed Aquifer Recharge, which can serve as an “exit strategy” as GAS reserves deplete. Thus, this work complements the efforts of the Guarani Aquifer System Program by emphasizing the need to advance GAS management actions and offering insights to regional policymakers.