Drought variability is of crucial importance not only to farmers but also to people throughout the world who rely on food and resources from a region. Unfortunately, instrumental records provide only a limited picture of the size and severity of historical droughts as well as the factors impacting drought variability throughout the world.
Tree-ring data have been used 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, 1930s, and 1950s droughts in a broader temporal context.
The drought data are in the form of summer (June–August) averages of the Palmer Drought Severity Index (PDSI). Negative PDSI values indicate dry conditions, while positive values indicate wet conditions. PDSI values generally fall between -6 and +6.
Palmer Drought Severity Index Studies with Visualizations
Some of the PDSI reconstructions are available for visualization on NCDC's Live Access Server (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 from the "Help" link in the upper right of the screen.
Monsoon Asia Drought Atlas (MADA) PDSI Dataset and LAS Visualization
Cook et al. 2010 reconstruction of summer PDSI covering Southeast Asia using a 2.5° x 2.5° grid. Temporal coverage is 1300–2005 AD. The full dataset is also available for download as a netCDF collection.
North American Drought Atlas (NADA) (Version 2a) and LAS Visualization
Cook et al. 2008 reconstruction of North American summer PDSI using a 2.5° x 2.5° grid. Updated PDSI values from Cook et al. 2004. Temporal coverage is 0–2006 AD. The full dataset is also available for download as a netCDF collection.
North American Drought Atlas and LAS Visualization
Cook et al. 2004 reconstruction of summer PDSI for most of North America using a 2.5° x 2.5° grid. Temporal coverage is 0–2003 AD. The full dataset is also available for download as a netCDF collection.
Additional Palmer Drought Severity Index Studies
Cook et al. 1999 PDSI Reconstruction
Covers the coterminous United States using a 155-point grid of 2° latitude x 3° longitude. Temporal coverage is 1700–1978 AD.
Zhang et al. 2004 PDSI Reconstruction
Uses the same coterminous United States grid and has the same temporal coverage as Cook et al. 1999.
Other Data Archives
NCDC Climate Monitoring
Explore NCDC's efforts to monitor and assess the state of the Earth's climate, including current levels of drought coverage.
North American Drought Atlas (2004 Version) Home Page
Lamont-Doherty Earth Observatory Tree Ring Lab archive of NADA drought reconstuctions. Includes additional PDSI maps and animations.
National Integrated Drought Information System (NIDIS)
Data portal that monitors current drought conditions and provides risk and impact assessment tools.