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Extreme austral winter precipitation events over the South-American Altiplano: regional atmospheric features

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Abstract

The South American Altiplano has a marked dry season during the austral winter (June to August, JJA). However, during this season synoptic meteorological conditions triggering heavy precipitation can damage socioeconomic activities, often causing the loss of human lives. Using daily in-situ precipitation data from 39 rain-gauge stations over the northern Altiplano (\(18^{\circ }\hbox {S}\)-\(15^{\circ }\hbox {S}\); \(> 3000\) m.a.s.l.) for the JJA season, we computed the historical percentile 90 (p90) and we identified extreme rainy days with precipitation higher than p90 in the 1980–2010 period. We identified 100 winter extreme precipitation events (WEPEs) over this region that can last between one to 16 days. The K-means analysis was applied to anomalies of geopotential height at 500 hPa from ERA-Interim data during the initial day or Day(0) of WEPEs lasting 1 day (42 cases), 2 days (19) and more than 2 days (39). We found 59 WEPEs characterized by an upper-level trough over the Peruvian-Chilean coast. At 850 hPa, these 59 WEPEs are also associated with cold surges along the eastern Central Andes, indicating an association between the upper-level trough and the cold surge in developing deep convection over the northern Altiplano. A lead-lag composite analysis further showed a significant lower- and mid-tropospheric moistening over the western Amazon 2 days before the onset of these 59 WEPEs, due to low-level northerly wind anomalies originating over equatorial South America. The other 41 WEPEs are associated with a low-level southerly wind regime crossing the equator and a mid-and upper-level low-pressure system over the Peruvian-Chilean coast. While the low-level southerly regime enhances mid-tropospheric moisture transport from the equator towards the Altiplano due to the developed shallow meridional circulation when propagating equatorward, a low-pressure system promotes intensification of upward motion, boosting the upslope moisture transport from the lowlands to the east of the Central Andes towards the Altiplano.

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Data availability

The in-situ precipitation data set analyzed during the current study are from the Data on climate and Extreme weather for the Central Andes (DECADE) project, and it could be downloaded from this link: https://www.geography.unibe.ch/research/climatology_group/research_projects/decade/index_eng.html.

Code availability

The custom codes used to analyze the data sets in the current study are available from the corresponding author on reasonable request.

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Acknowledgements

Research funding comes from the AMANECER-MOPGA project funded by ANR and IRD (ref. ANR-18-MPGA-0008) and the IDEX grants of the University Grenoble Alpes (UGA), the VASPAT project IDEX “IRS-Initiative de Recherche Stratégique” (part of the ANR project ANR-15-IDEX-02) of UGA. The IGE’s authors thanks the support of the Labex OSUG@2020 (Investissements d’avenir - ANR10 LABX56). Furthermore, Mathias Vuille was partially supported by NSF awards AGS-1702439, OISE-1743738, and EAR-2103041. The quality of this research was improved by the constant exchange of ideas with members of the C2H team from the IGE. We give special thanks to J. Ronchail, L. Li, Pedro Silva-Dias, Myriam Khodri, Serge Janicot and Vincent Moron for their contributions in the framework of H. Segura’s PhD. thesis committee.

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No funding was received for conducting this study.

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All authors contributed to the study’s conception and design. Material preparation, data collection, and analysis were performed by HS and JCE. The first draft of the manuscript was written by HS. JCE, CJ, TL, MV, and TC commented and edited on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Hans Segura.

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Segura, H., Espinoza, J.C., Junquas, C. et al. Extreme austral winter precipitation events over the South-American Altiplano: regional atmospheric features. Clim Dyn 59, 3069–3086 (2022). https://doi.org/10.1007/s00382-022-06240-1

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  • DOI: https://doi.org/10.1007/s00382-022-06240-1

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