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The Last 2,000 Years


A 2129-Year Reconstruction of Precipitation for Northwestern New Mexico, USA
Henri Grissino-Mayer
Complete Scientific Reference

El Malpais Precipitation Reconstruction Data from the WDC Paleoclimatology archive.

Summary:Photo courtesy of H. Grissino-Mayer
Extraordinarily long-lived trees have been found growing in the El Malpais volcanic field of west-central New Mexico. Although it seems incongruous to find long-lived trees growing in the seemingly harsh environment of these relatively recent (3,000-115,000 years) lava fields, there are good reasons why these trees exist in this area. The lava flows have created kipukas (isolated areas of original substrate and vegetation surrounded by more recent lava flows) that have escaped disturbances such as fire, grazing, logging, and agricultural practices, because of their isolation. The lava field also appears to trap and retain moisture in this otherwise arid environment, creating a habitat favorable to tree growth.

The oldest living tree found at this site is a 1274-year old Douglas-fir, the oldest known tree of this species in North America. Samples from this and other old trees were augmented with subfossil wood, from logs and remnants of living trees, to generate a 2129-year tree-ring chronology extending back to136 BC.

Not only are the El Malpais trees old, but they are sensitive to precipitation and thus, excellent recorders of past rainfall. The chronology was used to reconstruct annual precipitation for northwestern New Mexico for the past two millennia, as shown in the graph on this page (the units are standard deviation from the mean). The top graph shows the reconstruction for the years 1700-1992. The 1950s drought was the most severe drought 20th century drought in this region, but when viewed in the context of the past three centuries, it appears to be a fairly typical drought. However, when the 1950s drought is compared to droughts for the entire reconstruction, back to 136 BC (bottom graph), it is clear that the 1950s drought is minor relative to many past droughts. A number of the severe droughts of the past spanned several decades, the most recent occurring in the second half of the 16th century.

Back to... The Last 2000 Years.