Divergent Mechanisms Drive Multi‐Decadal Drought Intensification in South America: A Trend Turning Analysis From 1958 to 2023

Abstract

South America is undergoing an unprecedented drought crisis, threatening water security, ecosystem integrity and socioeconomic stability. While individual extreme drought events are well documented, the temporal evolution and mechanistic drivers of long‐term drought intensification remain poorly understood. Here, we employ the Running Slope Difference (RSD)– t ‐test method to analyse Palmer Drought Severity Index (PDSI) and soil moisture data, revealing two critical regime shifts in Central South America (CSA) drought patterns since 1958. We identify an abrupt transition from wet to dry conditions circa 1978, followed by a pronounced acceleration in drought severity post‐2012. Random Forest attribution analysis demonstrates that these regime shifts stem from distinct driving mechanisms. The 1978 transition primarily reflects precipitation deficits linked to large‐scale atmospheric circulation changes, including enhanced subsidence and tropospheric warming that suppress convective activity. In contrast, the post‐2012 acceleration is predominantly driven by elevated vapour pressure deficit (VPD), triggered by land surface feedbacks. Specifically, progressive vegetation loss reduces evapotranspiration, creating a positive feedback loop where decreased atmospheric moisture enhances VPD, accelerates soil moisture depletion and amplifies vegetation stress. This identification of temporally distinct drought intensification mechanisms provides crucial insights for regional climate adaptation strategies. Our findings suggest that while the 1978 regime shift reflected primarily atmospheric forcing, recent drought acceleration is increasingly modulated by land‐atmosphere feedbacks—highlighting the critical role of vegetation conservation in future drought resilience.

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