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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:
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.
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