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NOAA/NESDIS North American Drought Variability

US Drought Plot Dry Field Photo coralscape photo

Drought variability in North America is of crucial importance not only to farmers but to people throughout the world who rely on food and other materials from the region. Yet instrumented records provide only a limited picture of the occurrence of and factors impacting drought variability in the North American continent.

Dr. Edward R. Cook of the Lamont-Doherty Earth Observatory(LDEO) and colleagues used tree-ring data to extend records of past drought. The tree-ring reconstructions show a more complete range of drought variability than is provided by the 20th century instrumental record. The extended records are useful for placing the instrumental period droughts into a longer time frame, and for evaluating the rarity of the major 20th century droughts, the 1930s and 1950s, in a broader temporal context.

PDSI Annual Maps

View annual PDSI maps and Plot an average of multiple years.(Cook et al. 2004 Data)

PDSI Time Series

PDSI Time Series
View time series plots of PDSI data, and plot averages of multiple sites.(Cook et al. 2004 Data)

The drought data are in the form of summer (June-July-August) average Palmer Drought Severity Index. Negative PDSI values indicate dry conditions, while positive values indicate wet conditions. PDSI values generally fall between -6 and +6.

In 1999, a gridded network of PDSI reconstructions for the continental United States (Cook et al. 1999) were generated from a set of 388 tree-ring chronologies. Data are displayed in the form of annual contour maps, and in graphed time series for individual grid points. Maps and data from graphs can be downloaded, as well as the entire set of instrumental and reconstructed data.

In August 2004, the spatial and temporal coverage of the PDSI reconstructions
was expanded (Cook et al. 2004). The new grid includes 286 points in a
2.5 degree grid covering most of North America. The PDSI reconstructions are based on an expanded network of 835 tree-ring chronologies (602 western). The temporal coverage has been expanded to the maximum permitted by the available tree ring data, extending back nearly 2000 years for some locations. The instrumental PDSI series have been extended up through 2003. The new reconstructions are currently available from this site in numerical form and as time series plots (which can also be accessed via an Google Earth Map); the mapping display tools are being updated to display the expanded network.

Additional information on drought can be found in these recent publications. Also see our Paleo Perspective on North American Drought.

These pages were developed jointly by the NOAA Paleoclimatology Program,
the National Geophysical Data Center and the National Climatic Data Center. The 2004 reconstructions were funded by the Earth System History (ESH) of the National Science Foundation in a grant to E.R. Cook.

Note on PDSI visualizations

Some of the PDSI reconstructions are now available for visualization on NCDC's LAS page. Once on that page click the Choose Dataset button and then the Paleoclimate - Drought Reconstructions subdirectory to find the PDSI data. Plot settings can be modified using the 'Set Plot Options' button and multiple years can be compared using the 'Compare' button. Further information is available via the 'Help' link in the upper right of the screen.

arrow.gif (573 bytes)PDSI Data Links

Cook et al. 2010 Asian PDSI data set - Visualization Page (LAS) and netCDF collection of complete dataset.. (Cook et al. 2010)
Cook et al. 2008 N. American PDSI data set (Version 2a) - Visualization Page (LAS) and netCDF collection of complete dataset. Reconstructions only. (Contact Ed Cook for more information.)
Cook et al. 2004 North American PDSI data set - Visualization Page (LAS) and netCDF collection of reconstructions. (Cook et al. 2004 version, most of North America)
Zhang et al. 2004 PDSI time series page (Zhang et al. 2004, Uses Cook '99 grid, USA Only)
Cook et al. 1999 PDSI time series page (Cook et al. 1999 version, USA only)
Go to annual PDSI maps (1999 version, USA only)
NCDC Drought Pages
North American Drought Atlas (2004 version) at Lamont-Doherty Earth Observatory Tree Ring Lab. Includes additional PDSI maps and animations.
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