DOI 10.1007/s00382-010-0897-9 Forced and unforced variability of twentieth century North American droughts and pluvials

• Main Authors: Clim Dyn, Ron L. Miller, B. I. Cook, R. L. Miller, E. R. Cook, K. J. Anchukaitis, R. Seager
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2010
• Subjects: Pacific; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.188.5349; http://www.ldeo.columbia.edu/res/div/ocp/pub/seager/Cook_etal_20thC_2010.pdf

Abstract Research on the forcing of drought and pluvial events over North America is dominated by general circulation model experiments that often have operational limitations (e.g., computational expense, ability to simulate relevant processes, etc). We use a statistically based modeling approach to investigate sea surface temperature (SST) forcing of the twentieth century pluvial (1905–1917) and drought (1932–1939, 1948–1957, 1998–2002) events. A principal component (PC) analysis of Palmer Drought Severity Index (PDSI) from the North American Drought Atlas separates the drought variability into five leading modes accounting for 62 % of the underlying variance. Over the full period spanning these events (1900–2005), the first three PCs significantly correlate with SSTs in the equatorial Pacific (PC 1), North Pacific (PC 2), and North Atlantic (PC 3), with spatial patterns (as defined by the empirical orthogonal functions) consistent with our understanding of North American drought responses to SST forcing. We use a large ensemble statistical modeling approach to determine how successfully we can reproduce these drought/pluvial events using these three modes of variability. Using Pacific forcing only (PCs 1–2), we are able to reproduce the 1948–1957 drought and 1905–1917 pluvial above a 95 % random noise threshold in over 90% of the ensemble members; the addition of Atlantic forcing (PCs 1–2–3) provides only marginal improvement. For the 1998–2002 drought, Pacific forcing reproduces the drought