Because it’s hard to resist the word “megadrought” – or, frankly, the concept:
Tree rings from the headwaters of the Rio Grande show a 50-year drought from 122 to 172 AD, suggesting that “megadroughts” may be a recurring feature of the region’s climate, according to new research by a University of Arizona team.
Scientists have long known about similar drought a thousand years later that has been linked to the end of the early Native American culture of Chaco Canyon and the Four Corners area. But it was never clear whether that drought was unique.
The new evidence, being published in the journal Geophysical Research Letters, comes from a grove of bristlecone pine found by University of Arizona graduate student Cody Routson in the mountains near Summitville, Colo. He initially spotted the trees through binoculars during the summer of 2007, and returned in later years to take samples used to show the trees’ year-by-year growth.
Plus, I have an inordinate fondness for the tales tree rings tell
apropos – http://windupstories.com/pumpsix/the-tamarisk-hunter/
We don’t have the same opportunity to draw from tree rings in NZ. No Methuselah trees, and fewer water-limited species. But at least one study tells a similar tale to the Colorado reconstruction: recorded summer low flows are higher than the longer-term history from tree rings suggest is normal.
Daniel – What are the proxies used instead of tree rings?
Oh no, tree rings are used, but they don’t go back as far (bristlecone pine is an amazingly long-lived species), or the rings are not so well correlated with drought (NZ has a maritime clime and isn’t as dry). Kauri trees are used for long records, but they are limited to the very north (warm, dryer) part of the country. Only a few people are actually doing this research here.
Huh, interesting. That seems to correspond to a gap in the tree-ring record for the Durango Basketmaker II sites (and possibly the Cedar Mesa ones too). There are some radiocarbon dates that seem to fall into that interval, but radiocarbon doesn’t have the precision to shed much light on stuff like this.