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The year following a drought.
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Posted 8/2/2012 18:27 (#2518997)
Subject: The year following a drought.

39.48, -82.98

There is a thread below that asks what we can expect in the year following a drought year.

When I researched this I found there is no hard and fast definition of a drought year. NOAA has monthly data going back to 1895 for the contiguous 48 states, which they divide by region based of climatic consistency. I chose (for now) the central region, which includes MO, IL, IN, OH, WV, KY and TN. For a working definition of "drought" I used the mean summer (JJA) Palmer Drought Severity Index of < -3.00. From 1895 to 2011, ten years qualified: 1901, 1914, 1930, 1931, 1934, 1936, 1941, 1953, 1954, and 1988.

In some cases, we see back-to-back droughts. Other times, dry years were followed by wet years. The graph below shows the results visually, with each point representing two numbers -- the mean JJA PDSI of the drought year and that of the year following. The R-SQ statistic means that little more than 1% of the subsequent years' PDSI is explained by the drought years' PDSI. For such a small sample, this is insignificant. IOW, the odds of a drought in the central states next year is no greater than chance, which is roughly 10/117 (11/118, if 2012 ends up qualifying) or 9%.


Attachments drought_following_yr.gif (9KB - 48 downloads)
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