The West without Water by B. Lynn Ingram

Author:B. Lynn Ingram
Language: eng
Format: epub
ISBN: 9780520268555
Publisher: University of California Press

FIGURE 25. An ancient tree stump submerged in the West Walker River, eastern Sierra Nevada. (Photo courtesy of D. J. DePaolo, University of California, Berkeley.)

By counting the annual growth rings of these submerged trees, Stine showed that the trees had lived upward of 160 years. The droughts must have lasted at least that long to allow the trees to survive in that location. The trees were finally killed when the droughts ended abruptly, followed by dramatically high rainfall that rapidly raised the lake levels to drown them. Stine dated the outer growth layers of the tree stumps in Mono Lake and in other lakes and rivers in the central and eastern Sierra with radiocarbon methods. He found that the ages of all these trees clustered around two distinct periods: AD 900–1100 and AD 1200–1350.

Tree-ring studies from a broad region of North America indicate that climate conditions over the past 2,000 years became steadily more variable, with especially devastating droughts during this period as compared with earlier times. These records also suggest that the driest period in the West occurred between AD 900 and 1400. For instance, researcher Edward Cook and his colleagues at the Lamont Doherty Earth Observatory Tree Ring Laboratory in Palisades, New York, have studied tree-ring records that reflect the summer values of the Palmer Drought Severity Index—a measure of the moisture content of soil in the root zone. They compared tree-ring records from throughout North America and found that over half of the American West suffered severe drought between AD 1021 and 1051 as well as from AD 1130 to 1170, AD 1240 to 1265, and AD 1360 to 1382.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.