At its peak last summer, moderate to extreme drought gripped 61 percent of the Lower 48, but a "flash drought" brought exceptionally intense conditions to the Central Great Plains. Today, a new report by the NOAA Drought Task Force and the NOAA-led National Integrated Drought Information System (NIDIS) finds natural variations in weather patterns caused this sudden “flash drought,” and rules out global ocean conditions, as well as human-induced climate change, as major culprits.
The study finds that two key meteorological processes that bring rain were largely absent in the Plains last year. First, low pressure systems that normally produce widespread rains in May and June did not occur, as storm tracks produced by these systems were shunted northwards into Canada. Also, July and August thunderstorms, which are typically abundant in the region and deliver the majority of precipitation for the year, were infrequent and produced little rain. Using climate models, the researchers found that global ocean conditions had only a modest effect on these weather patterns, and therefore seasonal forecasts were unable to foresee the drought.
“Together, these conditions conspired to create a four-month sequence of record rainfall reduction over the central Great Plains,” according to the report which also attributes the drought to a “sequence of unfortunate events.”
The video above shows the preceding conditions, rapid onset, and evolution of drought conditions from November 2011-December 2012. Credit: NOAA Climate.gov.
The report addresses questions of interest to diverse stakeholders, including agriculture, land-use and resource planners, as to how and why the flash drought occurred. The report places the event into a 118-year historical context, addressing the conditions that led up to it, while also analyzing the performance of operational forecasts, and draws on lessons learned from climate science to improve drought forecasting.
The report found that the Central Plains drought of 2012 was not a progression or northward creep of the previous year’s Southern Plains drought event. In fact, there were no strong indicators that an extreme drought event was poised to spread over the Central Plains in 2012, consistent with the diagnosis that the event was due mostly to natural variations in weather.
The report examined nine previous severe summer droughts since 1895, and found no strong evidence for a progression of drought from the Southern Plains in one year to the Central Plains in the next. Although large portions of the United States are again experiencing a third year of drought, each individual drought event over the last few years has had different causes – with and without warning signs.
In terms of intensity, rainfall deficits from the 2012 summertime drought eclipsed any previous summer season drought in the Central Great Plains since recordkeeping began in 1895, including those of 1934 and 1936 during the Dust Bowl era, and another severe event in 1988.
“The fact that an extreme drought did occur in 2012 may thus be largely coincidental, and by the very nature of extreme events, its occurrence was a low probability outcome,” the report concludes.
After a relatively dry winter this year, drought remains entrenched across much of Plains and Southwest and, according to NOAA's Climate Prediction Center, is forecast to persist in many areas through spring 2013, although some limited improvement is possible in parts of the Plains. To view weekly updates on the drought, visit http://www.drought.gov/.
Hoerling worked with a team of 19 other federal and academic scientists as part of the Drought Task Force led by NOAA. The report was produced through a partnership between the NOAA Climate Program Office and NIDIS Program. It is available online at http://www.drought.gov/drought/content/resources/reports.
On the Web:
Frequently Asked Questions
NOAA Drought Task Force
NOAA National Integrated Drought Information System
Climate.gov 2012 Summer Drought Animation
Video: Baking the Breadbasket
[Web story contributed by Linda Joy, NOAA]