The U.S. Drought Monitor updates every week with Tuesday conditions being released on Thursday morning. This week, as of November 2, practically all of Southern Indiana has entered the severe drought category, with Ohio River basin areas in SE Indiana and as far north as Jackson County entering the exceptional drought category. The calculations used to define severe or exceptional drought are somewhat complicated, as they must take into effect precipitation, groundwater and streamflows, and soil moisture. Very generally, though, it can be said that a severe drought exists when the amount of available moisture is 6-10% of normal. An extreme drought can be said to exist when the moisture is 3-5% percent of normal.
On average, then, Southern Indiana should only experience these conditions once every 10-20 years. However, 2007 had similar conditions in Southern Indiana, although earlier in the year. With the rather wet 2008 and 2009 seasons, perhaps there is some validity to the extreme weather severity and frequency prediction from the Intergovernmental Panel on Climate Change?
To access the U.S. drought monitor, please visit the site, hosted by the University of Nebraska at Lincoln.