Megadrought‐Amplified River Geochemical Export in the Central Andes

The ongoing megadrought in the Central Andes has amplified hydrological and hydrochemical responses in mountain rivers. Using a 30‐year dataset (1995–2024) of suspended particulate matter (SPM), total dissolved solids (TDS), and major ions, together with streamflow and snow records, this study evaluates regime‐dependent responses in a glacierised, evaporite‐rich catchment (Tunuyán River, Argentina). Hydroclimatic analyses revealed a robust ~140‐day lag between snow accumulation and runoff, and a multi–annual snow–discharge coherence that weakened after 2010, coincident with the onset of the megadrought. Marked contrasts among wet, mean and dry regimes emerged primarily in magnitude and variability. Median SPM increased by ~240% from wet to dry years (387 to 1322 mg L −1 ), whereas TDS increased by ~31% (500–1300 mg L −1 ), driven mainly by Na + and Cl − (+78% and +76%, respectively), reflecting a regime‐dependent rebalancing of ionic composition under drought conditions. Despite higher solute concentrations, dry years exhibited stronger concentration–discharge coupling for specific solutes, with solute concentrations responding more strongly to discharge variability than under dilution‐buffered conditions. SPM displayed pronounced non‐linear intra‐annual hysteresis, with counter‐figure‐of‐eight loops dominating wet and dry years, while mean conditions were characterised mainly by clockwise behaviour. Export estimates showed strong regime dependence: annual SPM loads declined by ~45% and dissolved loads by 20%–60% from wet to dry years, consistent with reduced streamflow (−35%) and attenuated melt pulses. Nevertheless, the TDS–Q relationship remained remarkably stable over three decades ( b ≈ −0.25), reflecting persistent deep, buffered flowpaths, whereas particulate export became increasingly event‐driven. This study shows that sustained cryosphere loss and prolonged drought primarily amplify concentration levels and variability rather than reorganising export controls, increasing the vulnerability of Andean headwaters to water‐quality deterioration, with implications for other semi‐arid, glacierised Andean catchments.