Relic Groundwater and Mega Drought Confound Interpretations of Water
Sustainability and Lithium Extraction in Arid Lands
Abstract
Demand for lithium for batteries is growing rapidly with the global push
to decarbonize energy systems. The Salar de Atacama, Chile holds
~42% of the planet’s reserves in the form of brines
hosted in massive evaporite aquifers. The mining of these brines and
associated freshwater use has raised concerns over the sustainability of
lithium extraction, yet large uncertainties remain regarding fundamental
aspects of governing hydrological processes in these environments. This
incomplete understanding has led to the perpetuation of misconceptions
about what constitutes sustainable or renewable water use and therefore
what justifies responsible allocation. We present an integrated
hydrological assessment using tritium and stable oxygen & hydrogen
isotopes paired with remotely sensed and terrestrial hydroclimate data
to define unique sources of water distinguished by their residence time,
physical characteristics, and connectivity to modern climate. Our
results describe the impacts of major drought on surface and
groundwaters and demonstrate that nearly all inflow to the basin is
composed of water recharged >65 years ago. Still, modern
precipitation is critical to sustaining important wetlands around the
salar. Recent large rain events have increased surface water and
vegetation extents and terrestrial water storage while mining-related
water withdrawals have continued. As we show in this basin, poor
conceptualizations of these complex hydrological systems have
perpetuated the misallocation of water and the misattribution of
impacts. These fundamental issues apply to many similar regions
globally. Our new framework for hydrological assessment in these arid
basins moves beyond calculating gross inputs-outputs at a steady-state
to include all compartmentalized stores that constitute “modern”
budgets.