The Impact of Increased Aridity on Catchment Scale Sediment Flux in the Andes Mountains of Argentina and Chile

Streams and rivers sourced in the Andes Mountains of Argentina and Chile have long provided a lifeline to downstream foothill communities and a thriving agricultural sector. These same streams and rivers also serve as conduits for sediment derived from the high mountains. Future projected increases in aridity over the coming decades threaten to strain these water resources and alter long-term trends in the magnitude of sediment transport. Peak annual streamflow in the mountain catchments serving these communities is dominated by snowmelt from higher elevations and is particularly sensitive to changing climate conditions. Climate impacts reducing either the fraction of precipitation that falls as snow or the net amount of precipitation will alter the timing and magnitude of peak streamflow and the dynamics of sediment transport in ways yet unknown. In this study, we use historical observations of temperature and precipitation for a suite of high mountain catchments in Argentina and Chile to calibrate rainfall-runoff models of streamflow at the catchment outlets. We use a series of elevation bands in each model to split precipitation between rain and snow along a vertical profile and to simulate snow storage. We then couple modeled streamflow with sediment rating curves at each site and compare our results to historical observations of sediment flux. To estimate future changes in sediment flux, we use a stochastic weather generator to create time series of precipitation and temperature based on end-member future climate scenarios. By combining these future scenarios with calibrated streamflow models and sediment rating curves, we are able to forecast a range of likely responses in sediment flux. Our results have implications for the management of water quality in the region and contribute to efforts to study the interaction between changing climate conditions, hydrological processes, and sediment transport.