A robust null hypothesis for the potential causes of megadrought in Western North America

Toby R. Ault, Scott St. George, Jason E. Smerdon, Sloan Coats, Justin S. Mankin, Carlos M. Carrillo, Benjamin I. Cook, Samantha Stevensong

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The western United States was affected by several megadroughts during the last 1200 years, most prominently during the Medieval Climate Anomaly (MCA; 800 to 1300 CE). A null hypothesis is developed to test the possibility that, given a sufficiently long period of time, these events are inevitable and occur purely as a consequence of internal climate variability. The null distribution of this hypothesis is populated by a linear inverse model (LIM) constructed from global sea surface temperature anomalies and self-calibrated Palmer drought severity index data for North America. Despite being trained only on seasonal data from the late twentieth century, the LIM produces megadroughts that are comparable in their duration, spatial scale, and magnitude to the most severe events of the last 12 centuries. The null hypothesis therefore cannot be rejected with much confidence when considering these features of megadrought, meaning that similar events are possible today, even without any changes to boundary conditions. In contrast, the observed clustering of megadroughts in the MCA, as well as the change in mean hydroclimate between the MCA and the 1500-2000 period, are more likely to have been caused by either external forcing or by internal climate variability not well sampled during the latter half of the twentieth century. Finally, the results demonstrate that the LIM is a viable tool for determining whether paleoclimate reconstructions events should be ascribed to external forcings or to "out of sample" climate mechanisms, or if they are consistent with the variability observed during the recent period.

Original languageEnglish (US)
Pages (from-to)3-24
Number of pages22
JournalJournal of Climate
Volume31
Issue number1
DOIs
StatePublished - Jan 1 2018

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climate
twentieth century
Medieval
paleoclimate
temperature anomaly
boundary condition
sea surface temperature
drought
anomaly
North America
distribution
index
test

Keywords

  • Decadal variability
  • Drought
  • ENSO
  • North America
  • Tree rings

Cite this

Ault, T. R., St. George, S., Smerdon, J. E., Coats, S., Mankin, J. S., Carrillo, C. M., ... Stevensong, S. (2018). A robust null hypothesis for the potential causes of megadrought in Western North America. Journal of Climate, 31(1), 3-24. https://doi.org/10.1175/JCLI-D-17-0154.1

A robust null hypothesis for the potential causes of megadrought in Western North America. / Ault, Toby R.; St. George, Scott; Smerdon, Jason E.; Coats, Sloan; Mankin, Justin S.; Carrillo, Carlos M.; Cook, Benjamin I.; Stevensong, Samantha.

In: Journal of Climate, Vol. 31, No. 1, 01.01.2018, p. 3-24.

Research output: Contribution to journalArticle

Ault, TR, St. George, S, Smerdon, JE, Coats, S, Mankin, JS, Carrillo, CM, Cook, BI & Stevensong, S 2018, 'A robust null hypothesis for the potential causes of megadrought in Western North America', Journal of Climate, vol. 31, no. 1, pp. 3-24. https://doi.org/10.1175/JCLI-D-17-0154.1
Ault, Toby R. ; St. George, Scott ; Smerdon, Jason E. ; Coats, Sloan ; Mankin, Justin S. ; Carrillo, Carlos M. ; Cook, Benjamin I. ; Stevensong, Samantha. / A robust null hypothesis for the potential causes of megadrought in Western North America. In: Journal of Climate. 2018 ; Vol. 31, No. 1. pp. 3-24.
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