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Three and a Half Centuries of Droughts in the American Southeast
Pederson, N., Bell, A.R., Knight, T.A., Leland, C., Malcomb, N., Anchukaitis, K.J., Tackett, K., Scheff, J., Brice, A., Catron, B., Blozan, W. and Riddle, J. 2012. A long-term perspective on a modern drought in the American Southeast. Environmental Research Letters 7: 10.1088/1748-9326/7/1/014034.

Climate alarmists are always warning us about the "fact" (as they see it) that continued business-as-usual anthropogenic CO2 emissions will lead to catastrophic global warming and concomitant disastrous increases in various types of extreme weather phenomena. One of these computer-generated bogeymen in the climatic realm is drought, which in the words of the authors is "a pervasive phenomenon throughout much of North America with profound ecological and societal implications," as has been suggested by the work of Hursh and Haasis (1931), Breshears et al. (2005), Manuel (2008) and Allen et al. (2010). And getting more specific, while citing Knight (2004) and Seager et al. (2009), they add that recent moisture deficits in the southeastern US have renewed water management challenges that underscore the need to "better understand drought processes in humid, subtropical regions," which is what they thus set out to do.

What was done
In the words of Pederson et al., "to put the region's recent drought variability in a long-term perspective, a dense and diverse tree-ring network - including the first records throughout the Apalachicola-Chattahoochee-Flint river basin - is used to reconstruct drought from 1665 to 2010," which network, as they describe it, "accounts for up to 58.1% of the annual variance in warm-season drought during the 20th century and captures wet eras during the middle to late 20th century."

What was learned
The twelve researchers say the Palmer Drought Severity Index reconstruction for their study region shows that "recent droughts are not unprecedented over the last 346 years," and that "droughts of extended duration occurred more frequently between 1696 and 1820," when most of the world was shivering in the midst of the Little Ice Age. And they also state that their results "confirm the findings of the first reconstruction of drought in the southern Appalachian Mountain region, which indicates that the mid-18th and early 20th centuries were the driest eras since 1700, citing Stahle et al. (1988), Cook et al. (1998) and Seager et al. (2009).

What it means
In a warning that is just the opposite of what the world's climate alarmists contend about drought-prone regions, Pederson et al. conclude that when preparing for the future, "it may be prudent for water resources planning in the American Southeast to consider the drier centuries of climate variability that precede current experience and [the] instrumental record."

Allen, C.D., Macalady, A.K., Chenchouni, H., Bachelet, D., McDowell, N., Vennetier, M., Kitzbereger, T., Rigling, A., Breshears, D.D., Hogg, E.H. (Ted), Gonzalez, P., Fensham, R., Zhang, Z., Castro, J., Demidova, N., Lim, J., Allard, G., Running, S.W., Semerci, A. and Cobb, N. 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. Forest Ecology and Management 259: 660-684.

Breshears, D.D., Cobb, N.S., Rich, P.M., Price, K.P., Allen, C.D., Balice, R.G., Romme, W.H., Kastens, J.H., Floyd, M.L., Belnap, J., Anderson, J.J., Myers, O.B. and Meyer, C.W. 2005. Regional vegetation die-off in response to global-change-type drought. Proceedings of the National Academy of Sciences USA 102: 15,144-15,148.

Cook, E.R., Kablack, M.A. and Jacoby, G.C. 1988. The 1986 drought in the southeastern United States - how rare an event was it? Journal of Geophysical Research 93: 14,257-14,260.

Hursh, C.R. and Haasis, F.W. 1931. Effects of 1925 summer drought on southern Appalachian hardwoods. Ecology 12: 380-386.

Knight, T. 2004. Reconstruction of Flint River Streamflow Using Tree-Rings. Water Policy Working Paper 2004/2005. Georgia Water Policy and Planning Center, Albany, Georgia, USA.

Manuel, J. 2008. Drought in the southeast: lessons for water management. Environmental and Health Perspectives 116: A168-A171.

Seager, R., Tzanova, A. and Nakamura, J. 2009. Drought in the southeastern United States: causes, variability over the last millennium, and the potential for future hydroclimate change. Journal of Climate 22: 5021-5045.

Stahle, D.W., Cleaveland, M.K. and Hehr, J.G. 1988. North Carolina climate changes reconstructed from tree rings: AD 372-1985. Science 240: 1517-1519.

Reviewed 19 September 2012