Deglaciation in the subtropical Andes has led to a peak in sediment delivery

Glaciers are thinning and retreating as climate warms, thus eroding less of the Earth’s surface. However, other hydrological factors in glacierized catchments are likely producing a transient increase in sediment delivery, resulting in ‘peak sediment’. Estimating the trajectory of the peak sediment is ecologically and socially important but scientifically challenging because of the delayed and non-linear response of glacier sediment export to climate forcing. This study used time series of suspended sediment concentration starting in the 1960s from 11 Andean rivers at subtropical latitudes to analyse past changes in sediment export and infer its future behaviour. The recent decade has experienced anomalously high sediment concentration in most glacierized catchments, but the 1970s experienced even higher values. Decadal variations in the relationship between sediment concentration and ice melt suggest that the magnitude of the current decade was lower due to reduced glacial sediment rather than other factors. Combining this result with the fact that glacial runoff is decreasing, it is inferred that, for most of the glacierized catchments, the peak sediment generated by the anthropogenic deglaciation started two centuries ago has already passed its maximum. The sediment delivery product of climate-change-driven deglaciation has passed its maximum for most of the subtropical Andes, according to the analysis of suspended sediment concentration from 11 rivers at subtropical latitudes.