The Data
Instrumental records of drought for the United States extend back approximately 100 years. These
records capture the major 20th century droughts, but are too short to assess the reoccurrence of major
droughts such as those of the 1930s and 1950s. As droughts continue to have increasingly costly and
devastating impacts on our society, economy and environment, it is becoming even more important to
put the severe droughts of the 20th century into a long-term perspective. This perspective can be
gained through the use of paleoclimatic records of drought.
Scientists have developed paleoclimatic records of drought from a variety of types of proxy data that
span the past hundreds to tens of thousands of years, and longer. These records demonstrate patterns
of natural drought variability and allow us to compare 20th century droughts with those of the past.
These records can also be examined in light of what we know about the circulation features that are
important to drought today, such as
ENSO . Research using both paleoclimatic records of
drought and circulation features can determine how slowly changing climate conditions may influence
periods of long or more frequent droughts.
The sections below highlight some of the data and studies for four catagories of time, beginning with the
20th century instrumental record of drought, and ending with paleoclimatic records of drought more
than two thousand years ago. These studies have yielded much information about climate and drought
conditions of the past and demonstrate the usefulness and importance of paleoclimate data.
- The Instrumental Record
This section highlights aspects of drought
concerning varying patterns of
drought and the relationship of ENSO to patterns of drought.
Links to other web pages on current drought, climate, and ENSO
conditions are included as well as information about obtaining
these records for the 20th century.
- The Last 500 Years
Droughts of the last four centuries are well documented in paleoclimatic proxies such as historical
documents and tree rings. Spatial patterns of drought for every year since 1700 have been generated
from a gridded network of tree-ring reconstructions and are featured in this section. Highlighted in this
section are those periods with droughts that appear to have been more severe than any we have
experienced in the 20th
century.
- The Last 2000 Years
A number of tree-ring records exist for the last two millennia which suggest that 20th century
droughts may be mild when evaluated in the context of this longer time frame. The evidence from long
tree-ring records is augmented with paleodrought records from other proxies, such as lake sediments
that reflect changes in salinity and precipitation/evaporation balances.
- Even Longer Records
Paleoclimatic data in this section document drought conditions back to the beginning of the Holocene
(10,000 years before present). These records demonstrate that North America experienced periods of
extremely dry conditions that were severe and sustained enough to result in the eastward expansion
of prairie into forested areas, fluctuations in lake levels, and mobilization of sand dunes over large
areas of the Great Plains which are now covered with vegetation. These changes are also reflected in
salinity and chemistry records from sediments of lakes in the northern Great Plains.
- Appendix of Drought Reconstruction Data Sets
On to... A Final Word .
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