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Climate change or climate regimes? Examining multi-annual variations in the frequency of precipitation extremes over the Argentine Pampas

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Abstract

A recent period of increased precipitation over the Argentinian Pampas expanded the boundary of rain-fed agriculture. However, such changes may not be sustainable if they arose from transient climate regime shifts. Considerable research exists on trends and cycles in sub-daily to annual precipitation metrics including the frequency and intensity of extreme precipitation. However, efforts to identify wetter and drier phases (or regimes) in this region are scant. This article aims to bridge that gap and advance our understanding of the multi-annual behavior of regional precipitation extremes, which can have the greatest impacts. It is unlikely that all extreme events are drawn from a single probability distribution or generated by the same physical processes. Hence, hidden mixtures of Poisson distributions are fitted to several precipitation frequency metrics to explore whether the annual to decadal variations in extreme precipitation frequency are greater than anticipated from a single system, and representative of regime shifts. Statistically significant improvements in the fit over single distributions were found for statistical mixture models of the frequency of very wet days, and the frequency of wet spells. This supports the hypothesis that multiple weather regimes exist giving rise to wetter or drier epochs. Posterior probabilities of hidden states from the fitted mixture distributions were used to identify wetter and drier years for comparison with sea surface temperature anomalies. This confirmed the presence of two distinct regimes, supporting other research, into the dynamical influences of precipitation behavior in the Argentine Pampas.

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Notes

  1. Joint World Meteorological Organization (WMO) Commission for Climatology (CCl)/World Climate Research Programme (WCRP) project on Climate Variability and Predictability (CLIVAR)/Joint WMO–Intergovernmental Oceanographic Commission of the United National Educational, Scientific and Cultural Organization (UNESCO) Technical Commission for Oceanography and Marine Meteorology (JCOMM) Expert Team on Climate Change Detection and Indices (ETCCDI: http://www.clivar.org/organization/etccdi).

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Acknowledgements

The National Center for Atmospheric Research is sponsored by the National Science Foundation (NSF). Support for this work was partially provided by NSF Grants: EaSM 1049109, CNH 0709689, and CR 1049099; and 1048829 to the NCAR Weather and Climate Assessment Program. Thanks to Guillermo Podésta for providing daily weather data for the Argentine Pampas; to Ming Ge for producing Fig. 10; to James Done for providing comments on a draft version of the manuscript; and to three anonymous reviewers who considerably improved the manuscript. All calculations were carried out in R (http://www.r-project.org/), using packages lubridate, mixtools and plyr.

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Correspondence to Mari R. Tye.

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Tye, M.R., Katz, R.W. & Rajagopalan, B. Climate change or climate regimes? Examining multi-annual variations in the frequency of precipitation extremes over the Argentine Pampas. Clim Dyn 53, 245–260 (2019). https://doi.org/10.1007/s00382-018-4581-9

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  • DOI: https://doi.org/10.1007/s00382-018-4581-9

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