DroughtsStudy finds 1934 had worst drought of last thousand years

Published 21 October 2014

A new study using a reconstruction of North American drought history over the last 1,000 years found that the drought of 1934 was the driest and most widespread of the last millennium. Using a tree-ring-based drought record from the years 1000 to 2005 and modern records, scientists found the 1934 drought was 30 percent more severe than the runner-up drought (in 1580) and extended across 71.6 percent of western North America. For comparison, the average extent of the 2012 drought was 59.7 percent.

1934 drought worst of preceding 1000 years // Source: noaa.gov

A new study using a reconstruction of North American drought history over the last 1,000 years found that the drought of 1934 was the driest and most widespread of the last millennium.

Using a tree-ring-based drought record from the years 1000 to 2005 and modern records, scientists from NASA and Lamont-Doherty Earth Observatory found the 1934 drought was 30 percent more severe than the runner-up drought (in 1580) and extended across 71.6 percent of western North America. For comparison, the average extent of the 2012 drought was 59.7 percent.

It was the worst by a large margin, falling pretty far outside the normal range of variability that we see in the record,” said climate scientist Ben Cook at NASA’s Goddard Institute for Space Studies in New York. Cook is lead author of the study, which will be published in the Oct. 17 edition of Geophysical Research Letters.

A NASA release reports that two sets of conditions led to the severity and extent of the 1934 drought. First, a high-pressure system in winter sat over the west coast of the United States and turned away wet weather — a pattern similar to that which occurred in the winter of 2013-14. Second, the spring of 1934 saw dust storms, caused by poor land management practices, suppress rainfall.

In combination then, these two different phenomena managed to bring almost the entire nation into a drought at that time,” said co-author Richard Seager, professor at the Lamont-Doherty Earth Observatory of Columbia University in New York. “The fact that it was the worst of the millennium was probably in part because of the human role.”

According to the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change, or IPCC, climate change is likely to make droughts in North America worse, and the southwest in particular is expected to become significantly drier as are summers in the central plains. Looking back one thousand years in time is one way to get a handle on the natural variability of droughts so that scientists can tease out anthropogenic effects — such as the dust storms of 1934.

“We want to understand droughts of the past to understand to what extent climate change might make it more or less likely that those events occur in the future,” Cook said.