Q: What technically defines a drought?

A: A drought is unusually dry weather with no rain for an extended period. The exact definition tends to vary depending on where you live, says Brent McRoberts of Texas A&M University. “If you lived in Florida and got only 30 inches of rain a year, that may be considered a drought if previous years have been below normal,” he says. “But in many Western U.S. states, 30 inches of rain would be almost double the amount of annual rain. Droughts can last months or even years. Climatologists measure such things as the normal rate of rain during a particular time and the amount of water in the soil and even in lakes and rivers. By studying this type of data, they can determine if a drought is mild, severe or extreme.”

Q: What are some of the longest droughts?

A: In the U.S., everyone tends to remember the “Dust Bowl” days of the early 1930s, adds McRoberts. “This was a natural disaster that lasted years and affected much of the Great Plains of the U.S., covering an estimated 50 million acres. It came in waves that stretched from 1934, 1936-37 and again from 1939-40. The blowing sand and dust were so dense it was called a ‘black blizzard.’ The longest worldwide drought was a rainless period of 14 consecutive years, from October 1903 to January 1918, at Arica, Chile. The drought of 1987-89 in the U.S. was one of the most severe, costing an estimated $39 billion in lost crops and damage, with 5.1 million acres of forest burned, including large fires in Yellowstone National Park. Some strange things tend to happen with wildlife during droughts. In 1999, a drought hit the Eastern U.S. and bears, searching for water and food, were seen just 10 miles from downtown Baltimore and inside several small towns in New Jersey.”

"Weather Whys" is a service of Texas A&M University's Department of Atmospheric Sciences.