Extreme Rainfall and Flooding in the Hyperarid Atacama Desert, Chile

Abstract:

In March 2015 unusual ocean and atmospheric conditions produced many years’ worth of rainfall in a ~48-hour period over northern Chile’s Atacama Desert, one of Earth’s driest regions. This extreme rainfall event, in combination with unique hydrologic and geomorphic factors, generated catastrophic flooding. Here we describe the hydrologic and geomorphic drivers of and responses to the 2015 Atacama floods. In the Salado River, we estimated a flood peak discharge of approximately 1000 m³/s, which caused widespread damage and high sediment loads. The sediment-rich nature of the flood resulted from erosion of channel bed, bank, and floodplain material (i.e., valley fill), rather than hillslope unraveling; hillslopes remained surprisingly intact despite their lack of vegetation. In the coastal city of Chañaral, flooding of the Salado River produced maximum water depths over 4.5 m, meters-thick mud deposition in buildings and along city streets, and coastal erosion. Anthropogenic factors increased the consequences of the flood and highlight the need for early-warning systems. The Atacama flooding has broad implications in the context of hazard reduction, erosion of contaminated legacy mine tailings, and the Atacama’s status as a terrestrial analog for Mars. Our presentation will also place the March 2015 floods in the broader context of extreme flooding in desert environments and the mediating effects of vegetation or lack thereof, also drawing on our long-term studies of floods, channel change, and vegetation in desert rivers in Arizona, USA, and on related work in other settings.