Temperature-driven shift intensifies 21st-century Amazon droughts

The Amazon Basin (AB) is experiencing an intensification of hydroclimatic extremes, with droughts becoming more frequent, widespread, longer, and severe in the 21st-century. While precipitation deficits have historically been the primary driver of these events, the role of rising air temperatures and the consequent increase of atmospheric evaporative demand (AED) remains poorly quantified. Understanding the relative contributions of these factors is crucial for assessing AB resilience and potential tipping points under ongoing global warming. Here, we analyzed drought evolution across the AB over 45 years (1980–2024) using the Standardized Precipitation-Evapotranspiration Index (SPEI) derived from ERA5-Land reanalysis data. To isolate the contribution of atmospheric evaporative demand (CAED) to drought severity, we compared the standard SPEI with a modified SPEI version based on constant climatological AED.

Furthermore, we applied a rarity index to systematically rank drought events by intensity and spatial extent, enabling a standardized comparison of the exceptional 2023/24 event with historical benchmarks. Our analysis reveals that the 2023/24 drought (AD-23/24) was the most extreme event on record, affecting over 88% of the basin’s area and having a magnitude four times that of the average of the previous top-5 droughts. Notably, the recurrence of high-ranking drought years since 2020 underscores a persistence of extreme conditions in the 2020s. Crucially, the CAED analysis uncovers a distinct temporal regime shift occurring after 2005. While earlier droughts were primarily precipitation-driven, the post-2005 era is characterized by a predominantly evapotranspiration-driven regime, in which climate change-induced warming significantly amplifies drought intensity through increased AED. This intensification is further linked to sea surface temperature anomalies in the Tropical Indian, Tropical Pacific, and North Atlantic oceans. These findings demonstrate that the AB has entered a new hydroclimatic phase in which temperature-driven AED is overtaking precipitation deficits as the primary driver of exceptional drought events. This shift suggests that warming is likely exacerbating drought severity, posing unprecedented challenges for ecosystem stability and water security in the region.