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Surface runoff, channel activation and sediment transport processes in desert environments have been convincingly shown to strongly depend on the duration and intensity of local and convective rainfall events. Among these environments, the Atacama, considered the driest desert on Earth, is situated in a remote and rugged area, where documentation of historical and recent hydro-sedimentary processes is rare. We characterize the hydrological processes in an endorheic watershed of the Atacama's Altiplano Desert, where the occurrence of flash floods was evaluated on event-based signatures of water and sediment in a small ephemeral playa. Twelve pits were dug in the playa, with five identified event sediment couplets, each corresponding to computed flood volumes that gave rise to transport and depositional events occurring between 1978 and 2019. Detailed topography allowed reconstruction of a 3D terrain model, from which we estimated a 11.3 t/yr/km2 local historic sediment yield. The timing of the older identified events did not match local rainfall records, and proved to be uncorrelated with occurrences of El Niño–Southern Oscillation (ENSO). This suggests a high spatial patchiness of rainfall events in terms of depth and intensity, and implies that small playa records are not necessarily always helpful in reconstructing the regional climatic history of the recent past. The sediment concentration and volume of the reconstructed hypercontracted events are not well corrected with the magnitude of the rainfall event, suggesting the important role played by variable sediment availability and connectivity at basin scale. This spatiotemporal variability plays a major role in understanding the present and historic hydro-sedimentary processes in the Atacama's altiplano. [Display omitted] • Five recent sediment-laden flood events have been identified in sedimentary records in a playa in the Atacama Desert. • Events are not directly related to ENSO episodes nor to regional climatic events. • Sediment concentration does not correlate with the magnitude of the rainfall event. [ABSTRACT FROM AUTHOR]

The lower Yellow River (YR) reach is one of the most typical and complex river channels in the world. The impact of human activities on the evolution of its channels is an important scientific issue that needs to be explored. Based on cross-sectional channel data measured at four typical hydrological stations in the lower YR during the period from 1965 to 2015 and the accompanying annual runoff and sediment data, the variation characteristics of the longitudinal slopes of the riverbeds, the width-depth ratio of the cross-sections, and the lateral migration of thalweg points were analyzed. The river phase coefficients (ξ = W 1/2/ H) of the YR channel across different years were further evaluated. Furthermore, the correlation relationship between the river phase coefficient, annual discharge, and sediment concentration was established. The results show that over the last five decades, the fluctuation of the longitudinal profile of the upper and lower parts of the lower YR was more obvious than that of the middle part, and the variation range of the width of the channel cross sections and the fluctuation of the mainstream line differed in 1965–1973, 1974–1980, 1981–1985, 1986–1999, and 2000–2015. The morphological parameters of the channel cross-section (ξ) were mainly affected by the annual average discharge and sediment concentration, and a good fitting relationship was found through quantitative analyses. Large reservoirs have the function of redistributing water and sediment yields and reducing peak discharges, thereby leading to changes in the erosion-deposition patterns and river morphologies of channels. • Reservoir operation greatly controls flow regime and sediment transport. • Thalweg points record the channel a cyclic process of siltation and erosion. • Channel dimensions under bank-full level respond to water-sediment changes. • River phase coefficient is a key parameter indicating channel morphological feature. • Construction of Xiaolangdi Reservoir has mitigated further channel shrinkage. [ABSTRACT FROM AUTHOR]