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Increasing precipitation volatility in twenty-first-century California


Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood—of which, California’s rapid transition from record multi-year dryness between 2012 and 2016 to extreme wetness during the 2016–2017 winter provides a dramatic example. Projected future changes in such dry-to-wet events, however, remain inadequately quantified, which we investigate here using the Community Earth System Model Large Ensemble of climate model simulations. Anthropogenic forcing is found to yield large twenty-first-century increases in the frequency of wet extremes, including a more than threefold increase in sub-seasonal events comparable to California’s ‘Great Flood of 1862’. Smaller but statistically robust increases in dry extremes are also apparent. As a consequence, a 25% to 100% increase in extreme dry-to-wet precipitation events is projected, despite only modest changes in mean precipitation. Such hydrological cycle intensification would seriously challenge California’s existing water storage, conveyance and flood control infrastructure.

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Fig. 1: Change in frequency of extremely wet seasons.
Fig. 2: Cumulative occurrence of extremely wet sub-seasonal storm sequences.
Fig. 3: Change in frequency of extremely dry seasons.
Fig. 4: Change in frequency of precipitation whiplash events.
Fig. 5: Shifts in precipitation seasonality.
Fig. 6: Large-scale atmospheric conditions linked to California precipitation extremes.


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Our work was supported by a grant from the University of California, Los Angeles Sustainable LA Grand Challenge (D.L.S., J.D.N. and A.H.), by National Science Foundation grant AGS-1540518 (J.D.N. and B.L.) and by US Department of Energy Grant 201603457-04 (A.H.). The NatureNet Science Fellows Program provided funding to D.L.S. through a collaboration between The Nature Conservancy and the University of California, Los Angeles.

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D.L.S., B.L., J.D.N, and A.H. conceived of the study and designed the analyses. D.L.S. and B.L. provided analysis tools and conducted the analyses. D.L.S. wrote the manuscript and B.L., J.D.N. and A.H. provided comments and feedback.

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Correspondence to Daniel L. Swain.

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Swain, D.L., Langenbrunner, B., Neelin, J.D. et al. Increasing precipitation volatility in twenty-first-century California. Nature Clim Change 8, 427–433 (2018).

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