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Two Centuries of Drought on the Eastern Mongolian Plateau

Paper Reviewed
Bao, G., Liu, Y., Liu, N. and Linderholm, H.W. 2015. Drought variability in eastern Mongolian Plateau and its linkages to the large-scale climate forcing. Climate Dynamics 44: 717-8733.

In a paper published in Climate Dynamics, Bao et al. (2015) note that the last two decades have seen some severe droughts that have been attributed by many people to CO2-induced global warming, making particular mention of a few that occurred in northern China and Mongolia. However, they question the veracity of this latter association in light of the fact that "limited meteorological data (most back to 1950s) impede our understanding of the possible processes and mechanisms of drought variability with a long-time scale over this large region." And they thus set out to reconstruct the average April-August precipitation variability of the last two centuries for the Hulun Buir region on the eastern edge of the Mongolian Plateau.

The four researchers accomplished their objective by working with tree-ring samples they collected from three sites of old growth Pinus sylvestris var. mongolica trees, from which they developed growth-climate relationships for the major April-August growth period, which indicated that the growth rings of the trees "were positively correlated with precipitation." And what did that record reveal?

Twenty two extremely dry years and twenty three extremely wet years (greater or less than one standard deviation from the mean) were identified in the precipitation proxy, accounting for 14.1 and 14.7 percent of the entire record, respectively. The five driest years (more than 2 standard deviations below the mean) occurred in 1907, 1987, 1951, 2007 and 1856. Of these droughts, the top three must have been exceedingly exquisite, as the authors make a point to note there were "several missing rings" in the various tree samples they had collected for those years. With respect to the top wettest years (more than 2 standard deviations above the man), that distinction went to 1957, 1868 and 1962.

Bao et al. next compared their record to other pluvial studies within and around their study region, of which they report "similar fluctuation patterns of drought and pluvial intervals existed in several available tree-ring-based hydroclimatic reconstructions and ours." And based on their record and this regional comparison, Bao et al. conclude that "the recent drought events from late 1990 to the present are not unusual in the context of the past several centuries." Once again, therefore, we have another reliable reconstruction that reveals there is nothing unusual, unnatural, or unprecedented about current (or past!) precipitation variability -- for either floods or droughts -- that would suggest a CO2-induced influence.

Posted 2 June 2015