Storylines of the 2015-2024 heat-related extremes in South America: a country-level attribution

Rising global temperatures have strongly affected South America, increasing drought frequency, duration, and temperatures. Accompanied by ENSO influences, the 2015-2024 decade featured a series of high-impact heat-related extremes that led to episodes of water scarcity, widespread wildfires, power outages, crop failures, among other socioeconomic impacts in several countries. The impacts of individual extreme events can vary substantially between countries, depending on differences in infrastructure and adaptation measures. Therefore, a systematic, country-level attribution of events of the last decade can provide further understanding of how global warming could affect the occurrence of heat extremes in alternative climates at a national scale. 

Using spectrally nudged storylines, we attribute the role of anthropogenic climate change by simulating historical events in cooler (pre-industrial) and warmer (+2K, +3K, +4K warming levels) climates. Here, we extend the approach beyond the usual single event attribution and analyze extremes of the entire decade. We focus our analysis on climate indices relevant to human health (warm days, warm nights, hot-humid days) and water security (extreme drought). Our results reveal a transition towards near-permanent conditions for some indices already in a +2K climate, such as year-long warm nights in Colombia, and months of extreme drought in Brazil and Bolivia. In future climates, all tropical and subtropical countries reach permanent conditions in at least one index. Southernmost countries like Chile and Argentina show summer-long extremes, while Uruguay stands out as a country with low sensitivity to global warming. Furthermore, different to present-day climate, under warmer conditions, years with or without the influence of El Niño show a comparable behavior. These findings underscore the need for country-specific adaptation strategies in a warming climate.