1. Recent African drought heralds drier conditions to come
Human-induced climate change is projected to cause drier conditions in the midlatitudes. To assess whether the onset of drier conditions has already begun, Touchan et al. study newly developed multicentury tree ring records from Tunisia and Algeria for a longer-term perspective on drought in northwestern Africa. Using a new set of 13 chronologies from Atlas cedars (Cedrus atlantica) and Aleppo pines (Pinus halepensis), the authors analyze the widths of individual tree rings, following the basic principle that thinner bands indicate years when water was relatively scarce. Through this, they reconstruct the region's Palmer Drought Severity Index, an index of dryness based on precipitation and temperature, for the years between 1456 and 2002. The reconstruction reveals the magnitude of droughts from the historic record, despite there having been no instruments to record these droughts. Interestingly, the most recent drought (1999?) appears to be the worst since at least the middle of the fifteenth century. This drought is consistent with early signatures of a transition to more arid midlatitude conditions, as projected by several climate models.
Long term context for recent drought in northwestern Africa
Ramzi Touchan, David M. Melo, and Christopher Baisan: Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona, U.S.A.
Kevin J. Anchukaitis: Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, U.S.A.;
Said Attalah: Department of Agronomy, Faculty of Science, University of Ourgla, Ourgla, Algeria;
Ali Aloui: Institute of Sylvo-Pastoral of Tabarka, Tabarka, Tunisia.
Geophysical Research Letters (GRL) paper 10.1029/2008GL034264, 2008; http://dx.doi.org/10.1029/2008GL034264
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American Geophysical Union