Hydrographic shifts in coastal waters relect climate‑driven changes in hydrological regimes across Northwestern Patagonia

Resumen: Climate‑driven changes in freshwater inputs have been shown to affect the structure and function of coastal ecosystems. We evaluated changes in the inluence of river runoff on coastal systems of
Northwestern Patagonia (NWP) over recent decades (1993–2021) by combined analysis of long‑term streamlow time series, hydrological simulation, satellite‑derived and reanalysis data on sea surface conditions (temperature, turbidity, and salinity). Signiicant decreases in minimum streamlow across a zone spanning six major river basins were evident at weekly, monthly, and seasonal scales. These changes have been most pronounced in mixed‑regime northern basins (e.g., Puelo River) but appear to be progressing southward to rivers characterised by a nival regime. In the adjacent two‑layer inner sea, reduced freshwater input corresponds with a shallower halocline and increased surface temperatures across northern Patagonia. Our results underscore the rapidly evolving inluence of rivers on adjacent estuarine and coastal waters in NWP. We highlight the need for cross‑ecosystem observation, forecasting, mitigation and adaptation strategies in a changing climate, together with corresponding adaptive basin management of systems that supply runof to the coastal marine waters.