| With the realignment of the NOAA Paleoclimatology Program to the National Climatic Data Center in 2002, pre-instrumental data have been added to our climate status reports. Paleoclimatic data, especially tree-ring data and other annually dated records, can provide a perspective on the climate system before widespread instrumental data were available. Reliable national-scale instrumental (rain gauge and thermometer) data extend back to the beginning of the 20th century, which allows the computation of various measures of drought starting in January 1900 (see image to right). Other sources of data are needed to examine the national climatic history prior to 1900 (see image to left below).
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The graph to the left shows
the percentage area of the conterminous U.S. influenced by drought since
1400. The graph contains data both from instrumental records and from paleoclimatic
reconstructions based on tree-ring analysis. The time series consists of
the percent of the conterminous U.S. in severe drought each year, combining
the tree-ring reconstructed June-August Palmer Drought Severity Index (PDSI
=< -2) for 1400-1978 and instrumental June-August Modified Palmer Drought Severity
Index (PMDI =< -3) for 1979-2002. Correlation between the reconstruction
and instrumental values during the 1900-1978 overlap is 0.93. (The methodology
of the tree-ring reconstructed Palmer index is discussed in an article by
Cook et al., 1999; details are also available at the NOAA Paleoclimatology web site
and the August
2002 drought report page.)
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The graph above shows that droughts as widespread as this year’s
(approximately 36% of conterminous U.S. under severe drought conditions averaged
over the summer months) have occurred in each of the last six centuries.
More interesting is the presence of many periods of widespread drought that
lasted for a decade or longer. The tree ring data successfully reproduce
the broad spatial coverage of droughts of the early 1910s, mid-1920s, 1930s,
and 1950s. In 1934, the U.S. suffered the most widespread drought in the last
600 years. While not as widespread as the 1930s Dust Bowl, many droughts
in the 15th, 16th, and 19th centuries persisted for two decades or longer.
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In some regions, such as the U.S. Southwest and Mexico, droughts other than the Dust Bowl covered the most area. The figure to the left showing the tree-ring reconstructed drought area index for the southwestern U.S. indicates that the 1950s drought is clearly the most widespread of the century. However, the 16th century "Megadrought" was almost as widespread and lasted for over three decades.
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The drought of 2002 was moderately widespread and quite severe in some areas. This conclusion holds when compared to both the instrumental and the paleoclimatic record. In some areas, the drought of 2002 is as severe as any prior single year over the past several centuries. The figure to the right uses tree-ring data to compare the percent of annual average streamflow during the 2002 drought to prior centuries (1539-1999) for the Blue River in western Colorado (Woodhouse 2002). In this particular reconstruction, no drought in the record exceeds the magnitude of the 2002 drought, however seven prior years are not significantly different.
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Additional tree-ring data presented were compared with national-, regional- and local-scale droughts of this year. These include:
Additional National Data
Regional-Scale Pre-Instrumental Drought in the:
Local-Scale Pre-Instrumental Drought and Wildfires in:
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References:
- Cook, E.R., Meko, D.M., Stahle, D.W. and Cleaveland, M.K. 1999. "Drought reconstructions for the continental United States." Journal of Climate, 12:1145-1162.
- Cook, E.R., et al. 2002. personal communication. Full data set expected to be released in 2003.
- Woodhouse, C.A. 2002. personal communication.
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For further information, contact:
Jay Lawrimore
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Jay.Lawrimore@noaa.gov
-or-
Richard Heim
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Richard.Heim@noaa.gov
 NCDC / Climate Monitoring / Climate of 2002 / Annual / Search / Help
http://www.ncdc.noaa.gov/oa/climate/research/2002/ann/paleo-drought.html
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