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Extended Chronology of Drought in South Central, Southeastern and West Texas

Extended Chronology of Drought in South Central, Southeastern and West Texas

August 2011

Malcolm K. Cleaveland1, Todd H. Votteler2, Daniel K. Stahle3, Richard C. Casteel4, Jay L. Banner5

Note: Texas Parks and Wildlife Department produced a short video called Studying Cypress Trees, the Climate Detective available to the public on YouTube.

1 Corresponding Author; Professor Emeritus of Geography, Department of Geosciences, University of Arkansas, Fayetteville, AR 72701
2 Executive Manager of Intergovernmental Relations and Policy, Guadalupe-Blanco River Authority, 933 Court St., Seguin, TX 78155
3 Undergraduate student, Department of Geosciences, University of Arkansas, Fayetteville, AR 72701
4 Graduate student, Department of Geological Sciences, The University of Texas, Austin, TX 78712
5 Director of Environmental Science Institute, Department of Geological Sciences, The University of Texas, Austin, TX 78712


Abstract

Short instrumental climatic records prevent appropriate statistical and historical  characterization of extreme events such as the extent, duration, and severity of multi-year 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 three new baldcypress chronologies in South Central Texas and used them, with existing Douglas-fir chronologies from West Texas and a composite post oak chronology in Central Texas, to calibrate and reconstruct June Palmer Drought Severity Index (PDSI) in climate divisions 5 (Trans Pecos), 6 (Edwards Plateau), 7 (S. Central), and 8 (Upper Coast), from 1500-2008.  We validated the reconstructions against observed data not used in calibration.

Currently, most water planners use the decade-long drought of the 1950s (1948-57 or 1947-56) 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 four megadroughts 15- to 30-years long centered in central or northern Mexico.  This and previous studies indicate that Texas severe decadal-scale drought has occurred 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.