loading page

The January 2021 Zonal Atmospheric River in central Chile: a non-fatal disaster
  • Felipe Ugalde,
  • Cedomir Marangunic,
  • Ashley Apey
Felipe Ugalde
Geoestudios, Universidad de Chile

Corresponding Author:[email protected]

Author Profile
Cedomir Marangunic
Author Profile
Ashley Apey
Author Profile


Although scarcely described, intense summer precipitation events in central Chile aren’t an unknown phenomenon, their recurrence is estimated at 40 years. In the last 5 years, 2 heavy rainfall episodes triggered massive debris flows in the San Jose de Maipo county of the Metropolitan Region, located on the upper Maipo river basin, where average precipitation for summer months is only 7 mm. A summary of the current knowledge of the January 28 to 31, 2021 summer rain event is presented. The episode has been attributed to a Zonal Atmospheric River (ZAR), which allowed for a direct transfer of vapour and moisture on a W-E trajectory perpendicular to the Chilean coast. The latter favoured high altitude precipitation, with 0 degree isotherm estimated at 3.700 m a.s.l. On a local range, the snow line was observed between 2,800-3,100 m a.s.l. The event precipitation reached unprecedented values over 60 mm on all stations along the Maipo valley, with a local maximum of 117 mm. 3 pulses have been accounted for rainfall, with a maximum intensity of 11 mm/hour; at the peak of the pulses the Maipo river flow increased 8 times its pre-event flow of 60 m/s. In the following days after the event, 55% of the Upper Maipo basin was covered with snow. Due to sudden higher temperatures a consequent rapid snow melt increased the turbidity of the Maipo river, compromising freshwater supply. Agriculture was also affected, mainly grapes. According to the National Geological and Mining Service, over 120 landslides were triggered during the event, most of them being debris flows with some rock fall affecting the main roads. 700 persons were affected, more than 100 houses resulted with damages, 50 with severe damages and 33 destroyed, mostly at the San Alfonso village. Cost of infrastructure’s lost was estimated over US$4MM. Luckily, there weren’t any fatalities. This feature contrasts with the 25 February 2017 debris flow episode in the same region, with 8 fatal victims. Although local inhabitants have coexisted with this kind of hazards since historical times, uninterrupted urban growth on mountain areas has contributed substantially to an increase in the level of exposure. In this case, the accurate forecasting of the ZAR coupled with an effective risk communication avoided fatalities, nonetheless, it is most likely that this kind of phenomenon will occur again.