Hyperdroughts in central Chile: drivers, impacts, and projections

Abstract. Owing to the Mediterranean-like and highly variable climate of western South America, moderate droughts (20 %–30 % precipitation deficit) recur every 3–5 years in central Chile, alternating with wet years. Since 2010, however, this region has experienced a continuous dry spell, including extremely dry conditions in 2019 and 2021, when annual precipitation deficits exceeded 75 %. The substantial lack of rain in those winters resulted in severe environmental impacts (e.g., near collapse of natural forests) and augmented social tensions in the country. Long-term records reveal similar extreme dry conditions in 1924, 1968, and 1998, referred to as hyperdroughts (HDs). The climate drivers, past recurrence, environmental impacts, and social effects of HDs are documented here using station-based hydroclimate observations, meteorological reanalysis, tree-ring-based precipitation reconstructions, satellite-based vegetation products, and interviews with social actors. Large-ensemble climate model outputs are employed to assess changes in the recurrence and intensity of HDs in the near future. This task sheds light on the functioning of the atmosphere–hydrosphere–biosphere–social system in a Mediterranean-like region under extreme events and is timely given the prospect of a drier climate for central Chile during the rest of the 21st century. Overall, we found that the acute impacts of the HDs are modulated by precedent conditions, mainly in those systems with long memory (e.g., groundwater and vegetation) and the social context in which they occur (e.g., rural population fraction). Furthermore, extremely low precipitation causes some systems to react in a way that substantially departs from the climate-response relationship established under more benign conditions, including moderate droughts.