On the nature and attribution of severe droughts in the Amazon and Orinoco River basins in 2023 and 2024

As anthropogenic emissions of greenhouse gasses continue to increase, in 2024 we have experienced the hottest year on observational record globally, while the last ten years are the warmest ten years. Accelerating global climate change is intensifying the water cycle, leading to more frequent and/or severe droughts and floods as well as rapid transition between these opposite extremes in many parts of the world. Wide areas of the Amazon and Orinoco watersheds have endured severe drought in 2023 (the 2^nd hottest year on record) and 2024 while El Niño-Southern Oscillation (ENSO, the dominant mode of internal climate variability at interannual timescales) was in El Niño (positive) phase and neutral conditions for most of this time. Some of the Amazon’s largest tributaries dropped to their lowest levels since records began in 1902, while more than 1700 schools and 760 health centres in the Amazon were inaccessible or out of reach at least at one point in the last two years. 

We examine dynamic and thermodynamic mechanisms leading to drought in both dry (JJASON) and wet (DJFMAM) seasons and their multiple combinations in the Amazon and Orinoco watersheds in 2023 and 2024. We employ multi-method attribution analysis to reveal the role of climate change leading to such prolonged and impactful drought conditions in this wider tropical region of the South America. We combine observational and reanalysis products with large ensembles of CMIP5/6 historical simulations and future projections to analyse the role of climate change and ENSO leading to these extreme events on timescales from six months to two years. We also use Met Office HadGEM3-A attribution system to assesses to what extent anthropogenic forcing has modified the probability and magnitude of multiple classes of meteorological droughts in the region experienced over the last two years. We explore both dynamically unconditional and conditional perspectives in our attribution analysis. Preliminary results point to a key role of climate change in likelihood and intensity of such droughts in both dry and wet seasons as well as from annual perspective in 2023 and 2024.