LAND SURFACE IMPACTS OF MARCH 24-26, 2015, ATACAMA DESERT PRECIPITATION EVENT

A precipitation event in the Atacama Desert of northern Chile March 24-26, 2015, was rare in several attributes: spatial extent, percentage of that area which received rain rather than snow, duration, and amount. The event provided an opportunity to document land surface consequences of precipitation in Earth’s driest desert, based on station data, satellite data, and field observation. The event blanketed >200,000 km², from the Pacific Coast of Chile into Argentina, ~22°–32°S latitude, covering a variety of physiographic and soil provinces. Whereas the responsible atmospheric phenomenon, a cold upper level low, is not uncommon in winter, this summer season event was fed by tropical moisture. The warm air placed the rain/snow line uncommonly high, above 3600 m elevation, and therefore much of the west slope of the Andean Cordillera experienced rain and the impacts were immediate. Reported rainfall varied from ~10 mm at the coast to >85 mm in the eastern mountains (Domeyko Range and Andes). The region of most widespread heavy rain, 23°–27°S, is hyperarid. Here the geomorphic domains are dominated by low-slope surfaces mantled with either gypsic soil or alluvium, and few canyons with rivers funnel upland runoff to the coast. South of 27°S, a narrow band of heavy rain persisted along the Andean crest to 32°S, through a region of transition to arid and then semi-arid climate. There the dominant landforms are steep hillslopes, and numerous canyons with rivers flow to the Pacific. Between 25°–30°S several of the major rivers flooded and along the Salado and Copiapó Rivers destruction by flooding of infrastructure and homes was devastating. However, from 23°–27°S there was remarkably little erosion or deposition outside of these canyons. Even though steep slopes and/or bare rock experienced runoff, the low-relief surfaces and weakly consolidated materials facilitated absorption or infiltration, which reduced cumulative run-off and mitigated erosion, deposition, and damage.

Authors also include Carolina Gamboa and Javier Urrutia of Universidad Católica del Norte, Antofagasta, Chile.