Anasazi Rainfall

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. When records of drought for the last two millennia are examined, the major 20th century droughts appear to be relatively mild in comparison with other droughts that occurred within this time frame. Even the 16th century drought appears to be fairly modest, when compared to some early periods of drought. Although there are still a few high resolution, precisely dated, tree-ring records available that extend back 2,000 years, most of the paleodrought data that extends back this far are less precisely dated and more coarsely resolved. These records reflect periods of more frequent drought, or drier overall conditions rather than single drought events, so it difficult to compare droughts in these records with 20th century drought events. However, the 20th century can still be evaluated in this context, and we can assess whether parts of the 20th century or the 20th century as a whole were wetter or drier than in the past with these records.