NOAA/WDS Paleoclimatology - Texas 500 Year Palmer Drought Severity Index Reconstructions

STUDY NOTES: Tree-ring based Palmer Drought Severity Index (PDSI) reconstructions for 4 south-central Texas Climate Divisions over the past 500 years. The areas of the PDSI reconstructions are climate divisions 5 (Trans Pecos), 6 (Edwards Plateau), 7 (S. Central), and 8 (Upper Coast). The tree-ring data utilized in the reconstructions are archived in the International Tree-Ring Data Bank (ITRDB), available at: http://www.ncdc.noaa.gov/paleo/treering.html The chronologies used are: Guadalupe River State Park, TADI, ITRDB TX052 Krause Springs, TADI, ITRDB TX053 San Bernard River (Bates Allen Park), TADI, ITRDB TX054 South Texas Composite post oak, QUST, ITRDB TX049 Big Bend National Park, PSME, ITRDB TX001 Guadalupe Peak, PSME, ITRDB TX046 (also recollected in 2008)
ABSTRACT SUPPLIED BY ORIGINATOR: Short instrumental climatic records prevent appropriate statistical and historical characterization of extreme events such as the extent, duration, and severity of multiyear droughts. The best solution is to extend climatic records through well-understood proxies of climate. One of the best such proxies is climate-sensitive annual tree rings, which can be dated precisely to the year, are easily sampled, and are widely distributed. We created 3 new baldcypress chronologies in South Central Texas and used them, along with existing Douglas-fir chronologies from West Texas and a composite post oak chronology in Central Texas,to calibrate 1931-2008 and reconstruct June Palmer Drought Severity Index (PDSI) in Texas climate divisions 5 (Trans Pecos), 6 (Edwards Plateau), 7 (S. Central), and 8 (Upper Coast) 1500-2008. We validated the reconstructions against observed data not used in calibration. Most water planners in Texas at present use the drought of the 1950s, 1950-1956, as a worst-case scenario. Our reconstructions show, however, that a number of extended droughts of the past were longer and/or more intense than the 1950s drought. Furthermore, extended droughts have been a consistent feature of southwestern climate since the 800s, including at least 4megadroughts 15- to 30-years long centered in central or northern Mexico (Stahle et al. 2009; 2011b). This and previous studies indicate that severe decadal-scale droughts have occurred in Texas at least once a century since the 1500s. Current use by water planners of the 1950s drought as a worst-case scenario, therefore, is questionable. When water managers consider past droughts, population growth, and climate change, it becomes highly probable that the future poses unprecedented challenges.