Half a century of hydrological change in the Araguaia River: non-linear discharge trajectories in the largest free-flowing river of the Brazilian Cerrado

The Araguaia River, the largest free-flowing river entirely within the Brazilian Cerrado, offers an exceptional opportunity to assess long-term hydroclimatic change in a heavily transformed tropical basin. We analyzed discharge and precipitation records from 1970 to 2023 at four gauging stations to investigate temporal changes in river flow and their relationships with precipitation variability and land-use and land-cover change. The results do not support a simple linear trajectory of discharge decline. Instead, the hydrological record shows alternating phases of increase, relative stability, and decline. Mean annual discharge increased markedly from the 1970s to the late twentieth century, coinciding with wetter conditions and rapid landscape transformation, but a strong reduction has occurred since 2014. Across the four stations, mean annual flow decreased by about 26.6% from 2003-2013 to 2014-2023, while mean basin precipitation declined by about 18.0% over the same interval. These recent changes indicate that precipitation reduction is the main factor explaining the contemporary drop in discharge. However, the contrast between the early dry period and the recent decline suggests that runoff response in the basin has been modulated by more than one driver through time. We argue that hydrological change in the Araguaia reflects a non-linear interaction between climatic variability, long-term regional change, and land-use transformation, requiring caution in attributing discharge trends to single causes.