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Drought in the U.S. Corn Belt
Reference
Stambaugh, M.C., Guyette, R.P., McMurry, E.R., Cook, E.R., Meko, D.M. and Lupo, A.R. 2011. Drought duration and frequency in the U.S. corn belt during the last millennium (AD 992-2004). Agricultural and Forest Meteorology 151: 154-162.

Background
The authors write that "drought is among the most costly natural hazards affecting the United States, averaging $6 to $8 billion annually in damages, primarily in crop losses," and they say that "mitigating the impacts of drought through planning and preparedness has the potential to save billions of dollars."

What was done
Stambaugh et al., as they describe it, "used a new long tree-ring chronology developed from the central U.S. to reconstruct annual drought and characterize past drought duration, frequency, and cycles in the U.S. Corn Belt region during the last millennium." This new record, in their words, "is the first paleoclimate reconstruction achieved with subfossil oak wood in the U.S.," and they indicate that it "increases the current dendroclimatic record in the central U.S. agricultural region by over 500 years."

What was learned
Of great significance is the fact that the new drought reconstruction indicates that "drought conditions over the period of instrumental records (since 1895) do not exhibit the full range of variability, severity, or duration of droughts during the last millennium." As an example, the six scientists note that "three years in the last millennium were drier than 1934, a classic Dust-Bowl year and the driest year of the instrumental period," and that "three of the top ten most severe droughts occurred within a 25-year period corresponding to the late 16th century." Likewise, they state that "the four longest droughts occurred prior to Euro-American settlement of the region (ca. AD 1850)."

What it means
What's happened before can happen again; and major droughts have occurred in both cooler and warmer times in the past. In fact, the longest drought detected by Stambaugh et al. occurred in the middle of the Medieval Warm Period and, as they describe it, "lasted approximately 61 years (AD 1148-1208)." Therefore, people living in the United States should be keenly aware of the fact that the fabled Corn Belt of the country could become but a fleeting memory in a few short years -- or it could remain productive for many more years to come -- irrespective of whether the planet warms or cools.

Reviewed 9 February 2011