The Tree-Ring Drought Atlas Portal: A Suite of Research and Education Web Tools for Gridded Drought Reconstructions Over the Past 500–2000 Years

The North American Drought Atlas (NADA), first published in 1999, used a network of tree-ring chronologies across North America to derive gridded estimates of the long-term soil moisture balance integrated over the winter, spring, and summer seasons [i.e., the June-August Palmer Drought Severity Index (PDSI)]. The NADA was updated in 2004, and a website was developed to serve the 2.5 x 2.5-degree grid reconstructions to the scientific community. This website, housed at Lamont-Doherty Earth Observatory, has been widely used for research and education. However, the latest version of the NADA reconstructs June-August PDSI on a 0.5 x 0.5-degree grid over much of North America for the past 2000 years, and no user-friendly resources exist to leverage use of these reconstructions. Moreover, almost no user-friendly resources exist for the tree-ring drought atlases that have been developed in other areas of the world. A suite of webtools were developed for the recently published Mexican Drought Atlas, and are located on a server at the University of Memphis. These web-based capabilities have been applied to the other published tree-ring drought atlases (Eastern Australia and New Zealand, Monsoon Asia, and Old World). This “Tree-Ring Drought Atlas Portal” facilitates analysis of all the gridded reconstructions, where maps for individual years or any combination of years can be created and downloaded. Time series data for any single grid point or for a region can also be created and downloaded. Other analytical tools include correlation and congruence analyses. These web applications will not only allow students and scientists across multiple disciplines to make use of these reconstructions, but they will also provide a useful way for stakeholders and policy makers to assess the long-term history of droughts and pluvials over their regions of interest. Additional drought atlases are being reconstructed from tree rings, and will be added to this portal once they become available.