Protecting Environmental Flows to Achieve Long-Term Water Security
Environmental flows (e-flows) are intrinsically related to water security and water management: when the remaining flow of a river after upstream withdrawals is not enough to safeguarding ecological river functions, the basin is at extreme risk of water scarcity, which indicates that the water management is failing. To test this, we computed water stress indices (WSIs, computed as the ratio of withdrawals to water availability) for 277 basins in Chile, under two water-use scenarios: (i) WSI max , where withdrawals correspond to the maximum consumptive water allowed by the current law, and (ii) WSI alloc , where withdrawals correspond to the actual allocated consumptive water uses within the basins. We diagnose the water allocation system in Chile (defined by the Chilean Water Code) by assigning risks of water scarcity to the computed WSIs, and by contrasting the e-flows protected by law with those safeguarded by water management systems from six other countries.The Chilean Water Code incorporated the protection of minimum e-flows in 2005, but establishing that these do not exceed 20% of the mean annual streamflow, except in some exceptional cases. This limit is significantly lower than those used in other countries, where 20% to 80% of the mean annual streamflow are protected. This turns out in WSI max values between 80% and 100% in all basins, well above the threshold associated with over-committed basins under extreme risk of water scarcity (70% typically). The actual allocated withdrawals lead to contrasting results: about 70\% of the basins show low water scarcity risk (WSI alloc <40%), while a 18% have WSI alloc above 100%, indicating the allocation is going beyond current law limits and even beyond physical limits. Our results reveal that the link between water security, withdrawals and e-flows has not been adequately incorporated in the current water allocation system. E-flows stipulated by law are insufficient to fulfil environmental requirements, while placing the basins under extreme risk of water scarcity when the total allowed withdrawals are exerted. To move towards a system that can effectively achieve long-term water security, we recommend: (i) To declare tolerable water scarcity risks for basins that explicitly consider environmental requirements. (ii) To translate those risks into measurable basin indices to measure water security, such as the WSI. (iii) To set water use limits within the basins that are compatible to the water security goals. If, under current and projected water availability conditions, the existing withdrawals exceed these limits, water managers should be able to adapt total consumption to the required limits
Year of publication: |
2022
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Authors: | Alvarez-Garreton, Camila ; Boisier, Juan Pablo ; Billi, Marco ; Lefort, Inti ; Marinao, Rodrigo ; Barria, Pilar |
Publisher: |
[S.l.] : SSRN |
Subject: | Umweltschutz | Environmental protection | Wasserversorgung | Water supply | Gewässerschutz | Water conservation |
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