Friday, April 12, 2013

NIDIS Releases Drought Taskforce Report: An Interpretation of the Origins of the 2012 Central Great Plains Drought

Recently, National Integrated Drought Information System (NIDIS), a collaboration between NOAA, the U.S. Department of Agriculture, and the National Drought Mitigation Center released a Drought Taskforce Report titled An Interpretation of the Origins of the 2012 Central Great Plains Drought (2013).  According to the 50-page report, available here, and the summary report, the following issues are discussed:
Precipitation deficits for the period May through August 2012 were the most severe since official measurements began in 1895, eclipsing the driest summers of 1934 and 1936 that occurred during the height of the Dust Bowl. This prolonged period of precipitation deficits, along with above normal temperatures, resulted in the largest area of the contiguous United States in drought since the U.S. Drought Monitor began in January 2000. By early September, over three-quarters of the contiguous U.S. was experiencing at least abnormally dry conditions with nearly half of the region (the Central Plains in particular) experiencing unprecedented severe drought.
For a longer-term perspective, the Palmer Drought Severity Index (PDSI) for August 2012 is compared to a long-term PDSI average spanning from 1895 to 2000 (left) and identifies the core region of the drought to be the central Plains region, with the most extreme moisture deficits occurring over the western Plains (consistent with the Drought Monitor map). A central U.S. epicenter for the drought is also affirmed by the May-August standardized rainfall deficits (middle) with -2 standardized departures from the 1981 to 2010 long-term average being widespread from Colorado to Missouri. Much of the dry region also experienced hot temperatures (right). The combination of low rainfall and high temperatures is typically seen during summertime droughts over the central U.S.

The central Great Plains drought during May-August of 2012 resulted mostly from natural variations in weather.
  • Moist Gulf of Mexico air failed to stream northward in late spring as cyclone and frontal activity were shunted unusually northward.
  • Summertime thunderstorms were infrequent and when they did occur produced little rainfall.
  • Neither ocean states nor human-induced climate change, factors that can provide long-lead predictability, appeared to play significant roles in causing severe rainfall deficits over the major corn producing regions of central Great Plains.

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