Another report report, this one from the Congressional Research Service, may be of interest. See Stafford Act Declarations 1953-2011:Trends and Analyses, and Implications for Congress. Aug. 2012. (R42702)

As is true of the recent GAO report, noted in the posting below, there is a great deal of useful data presented in this report.
Researchers take note:  these two reports could be the basis of a useful analysis.