Climate storminess as a driver of surface processes and a limiting factor for topographic responses to rock uplift

In the south-central Andes, a long-term persistent pattern in climate aridity has been linked to sediment storage in mountain valleys and the resultant delaying of river steepening in response to rock uplift over millennia. This conceptual modelimplies that the landscape has a long-term trajectory for sediment export that may be sped up or slowed down by projected climate change. With this framing, we seek to investigate how changes in precipitation patterns and discharge regimes impact the transient evolution of a semi-arid, post glacial landscape and its physical processes. Changes in precipitation patterns and discharge regimes are understood to drive substrate erosion, sediment transport and changes in channel patterns and dimensions. They also alter vegetation, weathering regimes and catchment morphologies that influence sediment supply and slope-channel coupling. Using field data, we investigate how a sequence of floods has driven the conveyance of sediment through a semi-arid, postglacial landscape. Along the Rio Teno in Central Chile, we quantify changes in vertical bed structure, bed surface grain size, clast lithology, river morphology and slope-channel connectivity in March 2021 and again following an extreme and a large flood event in 2023. Our findings highlight the importance of including the full range of flood magnitudes that exceed critical entrainment thresholds in models of sediment export and landscape evolution. While extreme events do significant work in redistributing sediment within a catchment, it is the higher frequency, lower magnitude events and snowmelt cycles that evacuate sediment and reset base levels. In the context of climate change, a hydroclimate dominated by extreme floods in this landscape would likely result in greater sediment export from postglacial upper reaches, sediment storage within valleys in mid-reaches and lateral erosion and sediment export along the lowest reaches. This potential change has significant implications for understanding the fate of mountain landscapes and their human populations over the next century.