ALBERT

Description: The Atacama Desert in Chile was less arid during the mid-Pliocene (3.2 Ma BP) than today, but the reasons for the change are largely unknown. To better understand the physical processes, we perform unique experiments with the regional climate model WRF to downscale CESM2 output from PMIP4-CMIP6 to the kilometre-scale for the mid-Pliocene and present-day climate. Our experiments show more rainfall in the Desert for the mid-Pliocene, broadly consistent with proxy data. The detailed assessment of the results with machine learning techniques for dynamical analyses highlight stronger extreme rainfall events under the mid-Pliocene conditions, primarily during winter. These events are driven by stronger moisture conveyer belts (MCBs) with an origin in the tropical East Pacific. For the present-day climate, the model results suggest that MCBs are much weaker and stem from elsewhere, namely the subtropical Pacific. Although MCBs are rare with an occurrence on less than one day per year, they are regionally associated with more rainfall in the mid-Pliocene mean than what is simulated for present-day conditions. Our findings suggest that stronger MCBs are the main explanation for the increased rainfall in the Atacama Desert during the mid-Pliocene, possibly linked to warmer oceans paired with stronger mid-tropospheric troughs. When we interpret the mid-Pliocene as an analog for a +3K warmer world in the future, our results imply stronger rainfall extremes in the future of the Atacama Desert that are driven by similar but not identical weather patterns known from the recent past. Reyers et al., Clim. Past, https://doi.org/10.5194/cp-2022-72, 2023.