Background
Climate alarmists have long claimed that global warming leads to more frequent and severe episodes of various types of extreme weather phenomena. In the case of drought, for example, the authors write that "the IPCC (2007) and the U.S. Climate Report (Karl et al., 2009) predicted a rapid increase in air temperature, which would result in a higher evapotranspiration thereby reducing available water," with the result that "it is likely that drought intensity, frequency, and duration will increase in the future for the Southern United States."

What was done
Focusing on the period 1895-2007 - which includes the bulk of the transition from the Little Ice Age to the Current Warm Period, during which interval the world's climate alarmists claim the planet warmed at a rate and to a degree that were both unprecedented over the past millennium or more - Chen et al. used the standard precipitation index (SPI) to characterize both drought intensity and duration throughout the Southern United States (SUS).

What was learned
The nine researchers say they found "no obvious increases in drought duration and intensity during 1895-2007." In fact, they say they actually found "a slight (not significant) decreasing trend in drought intensity." And they emphatically state that "although reports from IPCC (2007) and the U.S. Climate Report (Karl et al., 2009) indicated that it is likely that drought intensity, frequency, and duration will increase in the future for the SUS, we did not find this trend in the historical data." And in like manner they write that although "the IPCC (2007) and U.S. Climate Report predicted a rapid increase in air temperature, which would result in a higher evapotranspiration thereby reducing available water," they also say they "found no obvious increase in air temperature for the entire SUS during 1895-2007."

What it means
Once again, the over-the-top contentions of both the IPCC and the authors of the U.S. Climate Report of 2009 are found to be without any confirmation whatsoever in pertinent real-world data.

References
IPCC. 2007. Climate Change 2007: The Physical Science Basis. Solomon, S., Qin, D., Manniing, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. and Miller, H.L. (Eds.), Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

Karl, T.R., Melillo, J.M. and Peterson, T.C. 2009. Global Climate Change Impacts in the United States. Cambridge University Press, Cambridge, United Kingdom.