The Last 2,000 Years

Data from this study archived at the WDC Paleoclimatology include the raw precipitation reconstruction and filtered precipitation reconstruction plus a description of the reconstruction , as well as the ringwidth measurements and standardized chronology for the Methuselah Walk tree ring site.

Summary:
An extensive network of tree ring chronologies of greater than 1000 years in length exists for the western United States. This multi-millennial-length tree ring chronology network provides an excellent opportunity to study decadal to century scale variability in pre-instrumental times. There are now 80 long chronologies available that are sensitive to a wide variety of environmental variables, including warm season temperature and winter precipitation.

In this study, 7979 years of annual (July-June) precipitation were reconstructed from bristlecone pine in the White Mountains of eastern California. The graph to the right shows a comparison between the instrumental (in blue) and reconstructed (in red) precipitation records. The reconstruction documents the occurrence of eight multi-decadal droughts, with the two most recent centered on A.D. 924 and A.D. 1299. The graph below shows the record since AD 1. The occurrence of these two droughts is validated by an independent lake-level record from the neighboring Sierra Nevada Mountains. The timing of coinciding low lake levels from the Mono Lake record (Stine 1994) is shown by the yellow bars. Droughts of this character, were they to occur today, would clearly have a devastating impact. Future work will focus on expanding the multi-millennial record of drought from tree rings and determining forcing mechanisms for these droughts.