Led by Ph.D. candidate Claire Rubbelke and Professor Tripti Bhattacharya of the Department of Earth and Environmental Sciences (EES), the research team analyzed organic molecules preserved in ocean sediments off South Africa's coast. These compounds retain hydrogen isotopes from ancient rainfall, providing a unique chemical snapshot of past climate conditions.
The study zeroed in on the Mid-Pleistocene Transition-between 1.25 and 0.7 million years ago-when major changes in Earth's glacial rhythms and atmospheric structure occurred. The team found that global shifts in atmospheric circulation during this time, especially fluctuations in the Hadley cell, led to alternating periods of drying and wetting in Southern Africa. These ancient dry spells bear a striking resemblance to the Day Zero drought that nearly depleted Cape Town's water supply between 2015 and 2020.
"We found that when the climate has changed dramatically in the past, it produced shifts analogous to the Day Zero drought," Bhattacharya said. "This suggests that those types of events are really driven by global climate change."
Rubbelke emphasized the potential implications for the future: "One big question I'm left with is whether these short droughts-and the Day Zero drought was relatively short-lived-will become more prolonged and eventually a permanent feature of the regional climate."
The research, which also involved contributions from undergraduate students Lucy Weisbeck and Ellen Jorgensen, has broader significance. Mediterranean climate regions like California could face similar threats. Understanding how ancient droughts unfolded may help refine modern climate models and enhance their reliability for future planning.
"Climate models are the only tool we have for planning," Bhattacharya added. "By testing how well they simulate past events, we can identify where they fall short-and ultimately improve our modeling capacity to better prepare for the future."
Research Report:Southern Hemisphere subtropical front impacts on Southern African hydroclimate across the Mid-Pleistocene Transition
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