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2012 Drought Rivals Dust Bowl
Nick Wiltgen
Jul 15, 2012, 10:34 AM EDT
weather.com



In a monthly report to be released Monday, the National Climatic Data Center is expected to announce that this year's drought now ranks among the ten largest drought areas in the past century.

Preliminary data computed from the Palmer Drought Severity Index shows that 54.6 percent of the contiguous 48 states was in drought at the end of June, the highest percentage since December 1956, and the sixth-highest peak percentage on record.

Monday's State of the Climate drought report from NCDC is expected to show that since 1895, only the extraordinary droughts of the 1930s and 1950s have covered more land area than the current drought.

And by a slight margin, the current drought actually covers more area than the famous 1936 drought, though other droughts in the Dust Bowl years – particularly the extreme drought of 1934 – still rank higher.


However, when excluding areas in "moderate" drought, the historical rankings change a bit. Some historical droughts were extremely intense, but more focused on specific regions rather than sprawling across large swaths of the country.

For example, infamous droughts in 1988, 2000, and 2002 each included over 35% of the country in the "severe" to "extreme" drought categories on the Palmer drought scale. By comparison, severe to extreme drought covers 32.7% in June 2012.

In short, the overall 2012 drought now covers more territory than any drought since the 1950s; but the more severe drought categories don't cover quite as much land now as did the droughts of 1988 and the early 2000s.

That being said, the 2012 drought still ranks as the 10th-largest severe drought since 1895, even by that stricter definition.

And with July typically being the hottest month of the year, the drought may yet worsen. Note that among the top ten largest "severe" droughts on record, five of them peaked in the months of July and August.

Different Drought Measures
In recent months, we have updated you on drought statistics from the U.S. Drought Monitor report. This weekly report is a collaboration between multiple government agencies that incorporates field reports, stream flows, soil moisture, snow pack, and other indicators to give a qualitative overview of drought conditions across the United States.

The Drought Monitor report debuted in 1999, and the period of detailed records began in January 2000.

One of the many inputs in the Drought Monitor report is the Palmer Drought Severity Index.



The weekly Palmer Drought Severity Index for July 14, 2012.

Large VersionThis index, developed by meteorologist Wayne Palmer in the 1960s, uses mathematical equations incorporating precipitation and temperature data to estimate evaporation, runoff, and soil moisture recharge.

Since these are fixed mathematical formulas, they can be applied retroactively to historical data, and the NCDC maintains a database of monthly Palmer drought indices dating to 1895. Some researchers have even calculated Palmer drought indices for the U.S. and other countries as far back as 1870.

Because of this much longer period of record, the Palmer index can be used as more of an "apples to apples" comparison between recent weather conditions and those from past decades, at least on a meteorological basis.

That being said, differences in land use and farming practices since the Dust Bowl make the comparison of real-world impacts more complicated. Erosion-control practices and drought-resistant crop hybrids are just two examples of ways in which modern agriculture attempts to mitigate the impacts of severe drought.

http://www.weather.com/news/drought-disaster-new-data-20120715