Publication Date : 2009-10-01
Author : Seager, R.Tzanova, A.Nakamura, J.
Countries :
Disaster Management Theme :
Disaster Type : Drought
Document Type : Research Paper
Languange : en
Link : http://journals.ametsoc.org/doi/pdf/10.1175/2009JCLI2683.1
Abstact :
An assessment of the nature and causes of drought in the southeastern United States is conducted as well as an assessment of model projections of anthropogenically forced hydroclimate change in this region. The study uses observations of precipitation, model simulations forced by historical SSTs from 1856 to 2007, tree-ring records of moisture availability over the last millennium, and climate change projections conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. From the perspective of the historicalrecord,therecentdrought thatbeganinwinter2005/06wasatypicaleventintermsofamplitudeand duration. Observationsand model simulations are used to showthatdry winterhalf-years in the Southeast are weakly associated with La Nin ˜as in the tropical Paci?c but that this link varies over time and was possibly of opposite sign from about 1922 to 1950. Summer-season precipitation variability in the Southeast appears governedbypurelyinternalatmosphericvariability.Assuch,modelsimulationsforcedbyhistoricalSSTshave very limited skill in reproducing the instrumental record of Southeast precipitation variability and actual predictive skill is also presumably low. Tree-ring records show that the twentieth century has been moist from the perspective of the last millennium and free of long and severe droughts that were abundant in previous centuries. The tree-ring records show a 21-yr-long uninterrupted drought in the mid-sixteenth century, a long period of dry conditions in the early to mid-nineteenth century, and that the Southeast was also affected by some of the medieval megadroughts centered in western North America. Climate model projections predict that in the near term, future precipitation in the Southeast will increase but that evaporation will also increase. The median of the projections predicts a modest reduction in the atmospheric supply of water vapor to the region; however, the multimodel ensemble exhibits considerable variation, with a quarter to a third of the models projecting an increase in precipitation minus evaporation. The recent drought, forced by reduced precipitationandwithreducedevaporation,hasnosignatureofmodel-projectedanthropogenicclimatechange.