Dr. Caamaño-Avendaño, Diego

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.

Data provided by products 3B42 V7 (TRMM) and its successor 3IMERG (GPM) are compared with discrete rainfall information throughout the Chilean territory covering four macro hydroclimatic zones. Precipitation data was obtained from weather stations available on a daily basis from the 1930s to present. A total of 143 stations were chosen and rainfall estimates performed for years 2014 through 2018. Applying the same metrics we showed how GPM performances improve as the temporal aggregation increases. Several drawbacks were detected in the coastal areas, which were characterized by lower accuracy performances than internal areas. However, the 3IMERG product could be a strong source of data to study the impact that climatic disturbances have on the hydrologic cycle in the Central and South zones of Chile. Additionally, its offers a fundamental source of data for remote zones or areas where access is complicated to install weather stations.